Work through these ten groups in order, because diagnosis conventions and E/M foundations support the later procedure and payer applications. Each concept pairs a rule with a short resolved example and a targeted mistake, so read the explanation, predict the example outcome, and check yourself. Keep current ICD-10-CM, CPT, and HCPCS code books beside you, since concepts reference their structures. These are teaching materials for exam preparation, not an official syllabus or a substitute for official resources.
ICD-10-CM Structure and Conventions
1. Index-Then-Tabular Workflow
Locate the main term in the Alphabetic Index first, follow all cross-references, then verify the code in the Tabular List, reading includes notes, excludes notes, and footnotes before finalizing. The Tabular List may add required characters or instructions the Index entry lacks.
Example: An index entry for external hemorrhoids points to K64.4; the coder verifies the code in the Tabular List before reporting it.
Mistake to avoid: Assigning a code straight from the Index without Tabular verification, missing instructional notes.
Reference: AAPC CGIC study guide sample; CDC ICD-10-CM Official Guidelines, FY 2027
2. Placeholder X and 7th Characters
Codes requiring a 7th character are invalid without it, and when the code is shorter than six characters, a placeholder X fills the empty positions. The 7th character must always occupy the seventh position in the data field.
Example: A five-character code in a 7th-character category needs one X plus the 7th character to be valid for submission.
Mistake to avoid: Reporting a 7th-character category code without the X placeholder or the 7th character itself.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
3. NEC Versus NOS Distinction
NOS (not otherwise specified) means the documentation lacks detail, so an unspecified code is used; NEC (not elsewhere classifiable) means the documentation is specific but no dedicated code exists, so an "other specified" code is used.
Example: Documented bile duct dilation has no unique code, so the other specified biliary tract code is correct rather than the unspecified one.
Mistake to avoid: Defaulting to the unspecified code when the documentation actually supports an other specified choice.
Reference: AAPC CGIC study guide sample; CDC ICD-10-CM Official Guidelines, FY 2027
4. Excludes1 Versus Excludes2
An Excludes1 note means the two conditions cannot be coded together; an Excludes2 note means the excluded condition is separate but may be coded together when both exist. Unrelated conditions are a recognized exception to Excludes1.
Example: Two conditions linked by an Excludes1 note but documented as clearly unrelated may both be reported after confirming their independence.
Mistake to avoid: Treating every Excludes note as a prohibition and dropping a legitimately coexisting Excludes2 condition.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
5. The With Convention Presumes Causation
The word "with" or "in" in a code title, index entry, or instructional note presumes a causal relationship, so the conditions are coded as related even without explicit provider linkage, unless documentation clearly states they are unrelated.
Example: An index entry joining a disease with a manifestation lets the coder report both as related despite no explicit linkage statement.
Mistake to avoid: Separating conditions the classification presumes related, or linking conditions with no relational term.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
6. Default Codes
A default code listed beside a main term represents the most common presentation or the unspecified form; assign it when a condition is documented without qualifying detail such as acute versus chronic or other subclassification.
Example: Documented appendicitis with no phase qualifier is assigned its default code rather than an acute-specific one.
Mistake to avoid: Skipping the default and guessing a more specific subtype the record never documents.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
Selecting and Validating Diagnoses
7. Suspected Diagnoses Are Not Coded
Uncertain terms such as probable, possible, suspected, likely, rule out, and consistent with are never coded. Report the highest level of certainty known, such as documented signs, symptoms, or abnormal test results, until confirmation exists.
Example: A provider suspects gastric cancer pending biopsy; the coder reports the documented symptom such as abdominal pain, not the cancer.
Mistake to avoid: Reporting a suspected neoplasm as if confirmed before pathology returns.
Reference: AAPC CGIC study guide sample; CDC ICD-10-CM Official Guidelines, FY 2027
8. Provider Statement Over Clinical Criteria
Code assignment rests on the provider's diagnostic statement that a condition exists, not on the clinical criteria the provider used to reach it. When record documentation conflicts, query the provider rather than exercising coder judgment.
Example: A provider documents a diagnosis despite atypical findings; the coder reports it without second-guessing the diagnostic reasoning.
Mistake to avoid: Overriding a provider's stated diagnosis because criteria seem unmet, or ignoring conflicting entries.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
9. Full Character Specificity
Only complete codes are reportable; categories and subcategories are not valid for claims. Select the highest specificity the documentation supports, and when required detail is missing, appropriate selection is impossible without obtaining provider clarification.
Example: A fracture code needing location, laterality, displacement, and episode characters cannot be finalized until each element is documented.
Mistake to avoid: Submitting a truncated subcategory where a full-length code with required characters exists.
Reference: AAPC CGIC study guide sample; CDC ICD-10-CM Official Guidelines, FY 2027
10. Appropriate Use of Unspecified Codes
Unspecified codes are correct when they most accurately reflect what is known at that encounter. It is inappropriate to select unsupported specific codes or conduct medically unnecessary testing just to obtain a more specific code.
Example: Pneumonia is diagnosed but not typed; the unspecified pneumonia code accurately reports the encounter.
Mistake to avoid: Assigning a specific code the record never supports simply to avoid an unspecified code.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
11. Other Clinicians' Documentation
Code assignment generally rests on the patient's provider, with limited exceptions such as BMI, laterality, pressure ulcer stage, coma scale, and social determinants of health, which other clinicians may document; the underlying diagnosis still requires the provider.
Example: A nurse documents ulcer staging, but the provider must document the ulcer diagnosis itself before both are reported.
Mistake to avoid: Building a diagnosis from ancillary staff notes when the provider never documented the condition.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
12. Interpreted Test Results in Outpatient Coding
When a previously interpreted diagnostic test's final report is available at the time of coding, report confirmed findings; if positive, code the findings instead of related symptoms, and if normal, code the sign or symptom that necessitated the study.
Example: A positive pathology report supersedes the testing indication; the confirmed finding is reported rather than the reason for testing.
Mistake to avoid: Coding the pre-test symptom alongside a confirmed definitive diagnosis from the final report.
Reference: AAPC CGIC study guide sample
Sequencing Rules and Special Diagnosis Situations
13. First-Listed Diagnosis Logic
In outpatient coding, the first-listed diagnosis is the main reason for the encounter, usually reflecting the chief complaint. Report chronic conditions as additional diagnoses only when treated or when they become an active factor in the patient's current care.
Example: A visit for heartburn control lists GERD first; stable, unaddressed hypertension is omitted unless it affected management.
Mistake to avoid: Sequencing a historical or inactive condition first instead of today's reason for the visit.
Reference: AAPC CGIC study guide sample
14. Acute and Chronic Together
When one condition is documented as both acute (subacute) and chronic and separate index subentries exist at the same indentation level, code both, sequencing the acute code first and the chronic code second.
Example: Documentated acute on chronic pancreatitis yields two codes with the acute form listed first.
Mistake to avoid: Choosing only one phase, or sequencing the chronic code ahead of the acute one.
Reference: AAPC CGIC study guide sample; CDC ICD-10-CM Official Guidelines, FY 2027
15. Sequela Coding
Sequela codes are usually reported as secondary diagnoses, with the current effect or reason for the visit as primary. There is no time limit within which late effects must occur, and residual deficits may appear at any time after onset.
Example: An old stroke's residual deficit is reported as a secondary sequela code with today's treatment reason sequenced first.
Mistake to avoid: Assigning a sequela code as first-listed, or assuming late effects expire after a set period.
Reference: AAPC CGIC study guide sample
16. Etiology and Manifestation Pairs
Where an underlying condition produces manifestations, sequence the etiology first, followed by the manifestation. A "use additional code" note appears at the etiology code, a "code first" note at the manifestation, and bracketed index codes always follow the etiology.
Example: An index pairing an underlying disease with its dementia manifestation sequences the disease first and the bracketed manifestation second.
Mistake to avoid: Reporting a manifestation code alone or sequencing it before its underlying etiology.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
17. Z08 Versus Z09 Follow-Up Encounters
Z08 reports follow-up after completed treatment for a malignant neoplasm, such as surveillance colonoscopy after colon cancer surgery; Z09 covers follow-up after completed treatment of other conditions such as infections, fractures, or benign conditions. Sequence the follow-up code first, then the personal history code.
Example: Routine surveillance colonoscopy after colon cancer treatment is coded Z08 first, then the personal history code.
Mistake to avoid: Using Z09 for cancer surveillance or omitting the accompanying personal history code.
Reference: AAPC CGIC study guide sample
18. Postoperative Pain and Complications
Routine, expected postoperative pain immediately after surgery is not coded. Postoperative pain not specified as acute or chronic is coded as acute, and pain tied to a documented complication is sequenced with the complication primary and a G89 category code secondary.
Example: Pain linked to a documented postprocedural complication reports the complication first, then the pain code.
Mistake to avoid: Coding expected routine postoperative pain, or sequencing the pain code ahead of the complication.
Reference: AAPC CGIC study guide sample
E/M Documentation Foundations
19. History and Exam Role in Leveling
Under current AMA guidelines, a medically appropriate history and/or examination is included in the service and should be documented, but history and exam are not used to determine the code level; leveling rests on MDM or total time.
Example: An extensive history alone cannot raise a visit whose MDM supports only a straightforward level.
Mistake to avoid: Leveling an office visit by counting exam elements as under prior documentation frameworks.
Reference: AAPC CGIC study guide sample
20. Choosing MDM or Total Time
The provider selects the E/M level by either the level of MDM or the total time for services performed on the date of the encounter, decided case by case. Whichever element is used, documentation must support the medical necessity of the visit.
Example: A visit meeting moderate MDM but modest time is leveled by MDM; the note supports the choice made.
Mistake to avoid: Mixing elements of both methods in one claim or leveling without medical-necessity support.
Reference: AAPC CGIC study guide sample
21. Core Documentation Principles
Documentation must be legible to someone other than the documenting provider and their staff, must readily demonstrate the date of service, patient name, and provider name, and must support the nature of the visit and the medical necessity of services rendered.
Example: An unsigned, illegible note fails verification regardless of the level billed.
Mistake to avoid: Accepting notes lacking identifiable provider, patient, or date elements as billable.
Reference: AAPC CGIC study guide sample
22. Code 99211 Without MDM
Code 99211 describes services that typically do not require the presence of a provider, so the concept of MDM does not apply to it; it is keyed to clinical staff work performed under physician supervision rather than physician decision making.
Example: A nurse visit for a documented, straightforward service with no provider presence fits 99211.
Mistake to avoid: Attempting to level 99211 by MDM components or billing it for provider-performed decision making.
Reference: AAPC CGIC study guide sample
23. New Versus Established MDM Mapping
The same MDM level maps to different codes for new versus established patients: straightforward, low, moderate, and high MDM correspond to distinct code pairs, so patient status must be resolved before code selection.
Example: Moderate MDM yields one code for a new patient and a different one for an established patient.
Mistake to avoid: Applying the new-patient code to an established patient with identical MDM.
Reference: AAPC CGIC study guide sample
24. Replaced Documentation Guidelines
The 2021 AMA revisions redefined office and other outpatient E/M codes, and in 2023 the same framework extended to other E/M categories, eliminating the 1995 and 1997 documentation guidelines from current use.
Example: A hospital E/M encounter is now leveled under the current framework, not the retired multi-system exam rules.
Mistake to avoid: Applying 1995 or 1997 documentation grids to any current E/M leveling.
Reference: AAPC CGIC study guide sample
Leveling Medical Decision Making
25. Problems Must Be Addressed
Only problems addressed within the encounter count toward the number and complexity of problems. Read the entire note rather than the chief complaint alone, because the full record reveals which conditions were truly assessed and managed.
Example: A note listing three complaints but addressing only one counts one problem for leveling.
Mistake to avoid: Counting every listed problem or relying only on the chief complaint when leveling.
Reference: AAPC CGIC study guide sample
26. Separately Reported Tests Do Not Count
Tests whose professional interpretation is separately reported by the physician, such as in-office imaging or ECG with separate interpretation billing, are excluded from data complexity. Results-only labs analyzed as part of MDM can be counted as ordered or reviewed.
Example: An in-office X-ray billed with separate interpretation is not counted as ordered data for the visit.
Mistake to avoid: Counting a separately billed interpretation toward data complexity for the same encounter.
Reference: AAPC CGIC study guide sample
27. No Double Counting Prior Orders
On a follow-up visit, reviewing the results of a unique test ordered at a previous visit is not counted again, because that review is included in the original ordering. Only new ordering or independent analysis adds data complexity.
Example: Discussing last week's lab results adds no new data point when those labs were ordered previously.
Mistake to avoid: Counting review of previously ordered test results as a second data element.
Reference: AAPC CGIC study guide sample
28. Comorbidities Must Be Addressed
Comorbidities and underlying diseases count toward risk only when the provider addresses them during the encounter or when they contribute to the severity of the case. Simply listing a chronic illness in the documentation is not sufficient.
Example: Documented diabetes mentioned only in the past history adds nothing to risk unless linked to today's management.
Mistake to avoid: Inflating risk by counting every chronic condition listed but never addressed.
Reference: AAPC CGIC study guide sample
29. Conditions Managed Elsewhere
When documentation only states that a condition exists and is being treated by another provider, it is not considered in leveling. Additional documentation showing assessment or care coordination beyond that statement makes the condition countable.
Example: A note adding a care-coordination discussion for an outside-managed condition allows it toward the level.
Mistake to avoid: Counting a passively mentioned outside-managed diagnosis toward problem complexity.
Reference: AAPC CGIC study guide sample
30. Diagnosis Alone Does Not Set Risk
The final diagnosis by itself does not determine complexity or risk, because extensive evaluation may be needed to conclude that signs or symptoms do not represent a highly morbid condition. Multiple lower-severity problems may aggregate to create higher risk through interaction.
Example: Reaching a benign conclusion after extensive workup still reflects the data and risk involved, not the benign label.
Mistake to avoid: Downcoding because the final diagnosis sounds minor while ignoring workup and combined risk.
Reference: AAPC CGIC study guide sample
E/M Special Billing Scenarios
31. Each Date of Service Stands Alone
Every ICD-10-CM code assigned must be supported by documentation linked to that particular claim, because individual dates of service stand alone. Conditions documented at earlier encounters are not carried onto today's claim unless the current encounter's documentation supports them, and coders must not assume or extrapolate from the historical record.
Example: A patient with gastritis documented at a February visit who returns in April for a new complaint has the April claim coded from April's documentation alone; February's gastritis is reported only if April's note shows it was treated or was an active factor in April's care.
Mistake to avoid: Pulling a prior-encounter diagnosis onto a new claim without documentation support from the current date of service.
Reference: AAPC CGIC study guide sample
32. Symptoms Cluster Around a Diagnosis
Per CPT, symptoms may cluster around a specific diagnosis, and each symptom is not necessarily a unique condition. When counting problems for MDM, symptoms the provider attributes to one diagnosed condition count as that single problem, not as separate problems.
Example: A visit for nausea, early satiety, and epigastric burning, all attributed by the provider to a single documented gastritis, addresses one problem for leveling, not three.
Mistake to avoid: Inflating the number of problems by counting each clustered symptom as a separate condition.
Reference: AAPC CGIC study guide sample
33. The Three MDM Components
MDM is selected based on three components: the number and complexity of problems addressed at the encounter; the amount and complexity of data to be reviewed and analyzed; and the risk of complications and/or morbidity or mortality of patient management. All three are extracted from the note before a level is chosen.
Example: Two visits addressing the same condition can level differently when one documents greater data review or higher-risk management, because the data and risk components differ even though the problem addressed is the same.
Mistake to avoid: Leveling a visit from the problem count alone without assessing the data and risk components.
Reference: AAPC CGIC study guide sample
34. Integral Symptoms Are Not Coded Separately
Signs and symptoms attributable to a definitive diagnosis are not reported separately. Cite additional signs and symptoms beyond the primary diagnosis only when they are not integral to the disease process, such as when the provider documents a reason to believe a symptom stems from an unrelated condition.
Example: A patient with documented ulcerative colitis whose abdominal cramping is integral to the colitis gets no separate symptom code; when the provider documents that new chest pain appears unrelated to the colitis, that symptom may be reported alongside the colitis diagnosis.
Mistake to avoid: Appending every documented symptom to a claim when the symptoms are integral to the confirmed diagnosis.
Reference: AAPC CGIC study guide sample
35. When a Condition Qualifies as a Complication
Not every condition that occurs during or following medical care or surgery is a complication. Code assignment rests on the provider's documentation of a cause-and-effect relationship between the condition and the care or procedure, and the condition must be clinically significant. The provider need not use the word "complication"; a condition that alters the course of the surgery as documented in the operative report supports a complication code, and unclear documentation warrants a query.
Example: A patient reporting bloating after a colonoscopy, with no documented link between the procedure and a clinically significant condition, does not support a complication code; a documented perforation that altered the procedure's course does, even though the word "complication" never appears in the note.
Mistake to avoid: Coding a post-procedure symptom as a complication without documented cause and effect, or withholding a complication code merely because the term was not used.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
36. E/M Categories and Subcategories
E/M codes are organized into categories such as office and other outpatient, hospital inpatient, and observation services, each with its own guidelines and subsection notes; code selection must stay within the correct category for the encounter setting.
Example: An office visit code is not selected for an inpatient encounter even with identical MDM.
Mistake to avoid: Pulling a code from the wrong category because the MDM level appears to match.
Reference: AAPC CGIC study guide sample
CPT Conventions and Procedure Sequencing
37. RVU-Ordered Procedure Sequencing
When multiple procedures are performed during one encounter, list the codes in descending relative value unit order, with the most complex or labor-intensive procedure first; an RVU calculator is available as a resource on the online exam, so the coder looks up the values rather than guessing which procedure ranks higher.
Example: A session in which a colonoscopy with polypectomy and a separately reportable EGD are both performed requires comparing the two codes' RVU values and listing whichever carries the higher value first, regardless of the order in which the note describes them.
Mistake to avoid: Sequencing procedures by the order performed in the note rather than by RVU value.
Reference: AAPC CGIC study guide sample
38. Modifier 51 for Additional Procedures
After sequencing procedures by RVU, append modifier 51 to subsequent non-bundled procedures to indicate an additional procedure performed during the same session. The modifier attaches to the additional code, never to the first-listed highest-value code.
Example: When an EGD and a colonoscopy are both separately reportable at one session, the code that sequences second, the lower-RVU additional procedure, carries modifier 51, and the first-listed code never does.
Mistake to avoid: Omitting modifier 51 on the lower-RVU additional procedure, or appending it to the first-listed code.
Reference: AAPC CGIC study guide sample
39. Parentheticals and Guidelines Govern Selection
CPT parenthetical phrases and section guidelines control code relationships, bundling, and reporting restrictions; reading them before selecting codes prevents choosing combinations the code book expressly links, excludes, or requires to be reported together.
Example: A parenthetical note directing separate reporting of two endoscopy components overrides an assumption that they bundle.
Mistake to avoid: Choosing codes from descriptors alone without checking surrounding guidelines and parentheticals.
Reference: AAPC CGIC study guide sample
40. Transplant Complications Code from Category T86
When a patient has a transplant and a complication related to that transplant, the primary code comes from category T86; the T86 transplant-complication code is sequenced first, ahead of any additional codes describing the complication's specific findings.
Example: A patient with a prior liver transplant who presents with a documented transplant-related complication is assigned the T86 category code as the primary diagnosis, with the specific complication findings reported as additional diagnoses.
Mistake to avoid: Sequencing the complication's manifestation first and omitting or demoting the T86 transplant complication code.
Reference: AAPC CGIC study guide sample
41. Sigmoidoscopy Anatomic Boundaries
Per the CPT digestive endoscopy definitions, sigmoidoscopy is an examination of the entire rectum and sigmoid colon, and may include visualization of a portion of the descending colon, but it does not examine the entire colon.
Example: A note documenting examination of the entire rectum and sigmoid with the scope entering the proximal descending colon still fits the sigmoidoscopy definition, because visualization of a portion of the descending colon is included; a colonoscopy code is not selected unless the entire colon is examined.
Mistake to avoid: Reporting a colonoscopy code when the scope never passed beyond the sigmoid and descending regions.
Reference: AAPC CGIC study guide sample
42. Polyp Definition for Coding Accuracy
A polyp is a mass of tissue that bulges outward or upward from membranes lining structures and organs; understanding this anatomy supports correct site identification and technique-based coding in gastroenterology procedures.
Example: A bulging mucosal mass identified in the sigmoid during endoscopy is documented and coded as a polyp, not a cyst.
Mistake to avoid: Confusing polyps with fluid-filled cysts or fatty sacs when interpreting operative findings.
Reference: AAPC CGIC study guide sample
Gastroenterology Procedure Coding Applications
43. Diagnostic Sigmoidoscopy Selection
A flexible sigmoidoscopy performed as a diagnostic examination with no therapeutic intervention is reported with the diagnostic code; the note's indication, the extent of scope advancement, and the documented findings drive the selection.
Example: A flexible sigmoidoscopy performed to evaluate chronic diarrhea, with the scope passed through the rectum and sigmoid and no biopsy or removal documented, reports the diagnostic code rather than a with-biopsy or therapeutic variant.
Mistake to avoid: Selecting a biopsy or therapeutic sigmoidoscopy code when only examination occurred.
Reference: AAPC CGIC study guide sample
44. EGD With Biopsy Components
An esophagogastroduodenoscopy that includes biopsy is reported with the EGD-with-biopsy code, with additional documented findings reported as additional diagnoses.
Example: An EGD performed for dysphagia in which the provider takes biopsies of the distal esophagus reports the EGD-with-biopsy code, with the documented esophageal findings reported as additional diagnoses.
Mistake to avoid: Reporting a plain diagnostic EGD code when the note documents biopsy performance.
Reference: AAPC CGIC study guide sample
45. Polyp Removal by Technique
Polypectomy codes are chosen by the removal technique used. If multiple polyps are removed using the same technique, report only one code; if different techniques are used, report a code for each technique, with a distinguishing modifier on the subsequent code.
Example: Four polyps removed during one colonoscopy, all by hot biopsy forceps, report a single polypectomy code for that technique; a second code becomes reportable only when another polyp is removed by a different technique.
Mistake to avoid: Reporting one code per polyp when a single technique removed them all.
Reference: AAPC CGIC study guide sample
46. Incomplete Colonoscopy Decision Tree
When a diagnostic colonoscopy is attempted but the colonoscope cannot be advanced to the cecum, a CPT decision tree directs the appropriate code selection and indicates when a modifier is or is not required, based on the extent of advancement.
Example: A scope unable to pass the sigmoid follows the decision tree's branch for limited advancement, including any required modifier.
Mistake to avoid: Reporting a full colonoscopy code when the scope never reached the cecum, ignoring the decision tree.
Reference: AAPC CGIC study guide sample
47. Postoperative Findings for Neoplasms
For neoplasm coding, review the postoperative diagnosis and operative findings to determine whether histology or behavior is specified; the entire operative note may clarify that a neoplasm initially described generically is benign.
Example: A postoperative diagnosis of gastric neoplasm, clarified by the operative findings as a benign lesion, is coded to benign behavior rather than left at an unspecified-behavior code drawn from the generic preoperative impression.
Mistake to avoid: Coding from the preoperative impression when findings specify the neoplasm's histology or behavior.
Reference: AAPC CGIC study guide sample
48. Postoperative Over Preoperative Diagnosis
When both a preoperative and a postoperative diagnosis are provided and they differ, always report the postoperative diagnosis, because the findings established at the procedure supersede the pre-procedure assumption.
Example: A colonoscopy undertaken for suspected polyposis whose findings show only diverticulosis reports diverticulosis as the diagnosis, because the postoperative finding supersedes the preprocedure suspicion.
Mistake to avoid: Reporting the preoperative diagnosis when procedure findings establish a different final diagnosis.
Reference: AAPC CGIC study guide sample
Medicare Context, HCPCS, and Payer Rules
49. CPT Default Unless Medicare Stated
On the exam, individual payer rules are not a consideration when choosing the right answer; unless it is specifically stated in the case note or question that the patient is covered by Medicare, follow the CPT coding guidelines.
Example: A case note silent on payer is coded purely by CPT guidelines, with no Medicare-specific assumptions.
Mistake to avoid: Applying Medicare policy to a case that never identifies the patient as a Medicare beneficiary.
Reference: AAPC CGIC study guide sample
50. HCPCS G Codes for Medicare
When an operative note indicates the patient has Medicare, report the applicable HCPCS Level II G code, such as the screening colonoscopy G code, instead of the comparable CPT code for that service.
Example: A Medicare patient's documented screening colonoscopy reports the G code rather than the CPT equivalent.
Mistake to avoid: Reporting the CPT code for a Medicare screening service that has an assigned G code.
Reference: AAPC CGIC study guide sample
51. Modifiers on HCPCS Level II Codes
It is appropriate to append CPT modifiers to HCPCS Level II codes; for example, modifier 51 can be appended to a G code to indicate an additional procedure performed during the same encounter.
Example: A G-code screening colonoscopy followed by a separately reportable procedure carries modifier 51 on the G code.
Mistake to avoid: Assuming modifiers apply only to CPT codes and leaving HCPCS codes unmodified.
Reference: AAPC CGIC study guide sample
52. Classification Instructions Take Precedence
Adherence to the ICD-10-CM Official Guidelines is required under HIPAA, and only the Cooperating Parties' approved set is official; however, the conventions and instructions of the classification itself, the Alphabetic Index and Tabular List, take precedence over the guidelines. When the two point in different directions, the code book's own instruction controls the assignment.
Example: When a Tabular List instructional note at a code calls for a different assignment than a general guideline's default handling, the coder follows the Tabular List instruction, because the classification's instructions outrank the guidelines.
Mistake to avoid: Applying a general guideline to override a specific instructional note printed at the code.
Reference: CDC ICD-10-CM Official Guidelines, FY 2027
53. Physician/QHP Work Versus Staff Work
Distinguishing physician or qualified healthcare professional work from clinical staff work determines whose service is billed and under which rules; physician-level decision making cannot be represented by tasks performed by clinical staff.
Example: A medical assistant recording vitals is staff work; interpreting results and establishing the plan is physician or QHP work.
Mistake to avoid: Billing clinical staff task time as physician or QHP service work.
Reference: AAPC CGIC study guide sample
54. Payer Regulations on Leveling Method
While the provider may choose MDM or total time on a case-by-case basis, payers may also have regulations on when each method is used, so the leveling approach must fit both the documentation and applicable payer requirements.
Example: A payer restricting a code family to time-based leveling requires documented total time rather than MDM support.
Mistake to avoid: Assuming the MDM-or-time choice is purely the provider's without checking payer constraints.
Reference: AAPC CGIC study guide sample
HIPAA Privacy and Compliance
55. Who Is a Covered Entity
The Privacy Rule applies to health plans, health care clearinghouses, and any health care provider who transmits health information electronically in connection with standard HIPAA transactions; merely using email does not make a provider a covered entity.
Example: A gastroenterology practice submitting electronic claims is covered; a practice never transmitting standard transactions may not be.
Mistake to avoid: Assuming every healthcare provider is covered regardless of electronic transaction activity.
Reference: HHS Summary of the HIPAA Privacy Rule
56. Protected Health Information Scope
Protected health information is individually identifiable information held or transmitted in any form, whether electronic, paper, or oral, that relates to health, care, or payment and identifies the individual; employment records and certain education records are excluded.
Example: A verbal hallway discussion of a patient's endoscopy result involves protected information.
Mistake to avoid: Treating oral or paper information as outside privacy protections.
Reference: HHS Summary of the HIPAA Privacy Rule
57. Minimum Necessary Standard
Covered entities must make reasonable efforts to use, disclose, and request only the minimum PHI needed to accomplish the intended purpose, and may not disclose an entire medical record unless specifically justified; treatment disclosures and individual access are exempt.
Example: A billing query sends only the procedure and diagnosis needed, not the full chart.
Mistake to avoid: Routinely disclosing whole medical records when a narrow data set would serve the purpose.
Reference: HHS Summary of the HIPAA Privacy Rule
58. Permitted Uses Versus Authorization
PHI may be used or disclosed without individual authorization for treatment, payment, and health care operations; uses outside these purposes, such as disclosures to a life insurer or an employer for a pre-employment physical, require written authorization.
Example: Sending results to the treating gastroenterologist needs no authorization; sending them to an employer for a physical requires authorization.
Mistake to avoid: Releasing PHI to an employer or insurer for non-TPO purposes without written authorization.
Reference: HHS Summary of the HIPAA Privacy Rule
59. Business Associate Agreements
A business associate is a person or organization outside the workforce that performs functions involving PHI for a covered entity, such as claims processing or billing; a written agreement imposing safeguards is required, and it may not authorize any violation of the rule.
Example: An outside billing service handling the practice's claims must operate under a signed business associate agreement.
Mistake to avoid: Sharing PHI with a contractor performing covered functions without a business associate agreement.
Reference: HHS Summary of the HIPAA Privacy Rule
60. De-Identification and Limited Data Sets
De-identified information, created by removing specified identifiers with no knowledge that the remainder could identify anyone, faces no use restrictions; a limited data set retains some identifiers and requires a data use agreement for research, operations, or public health purposes.
Example: A research project receiving dates of service without names operates under a limited data set agreement, not full de-identification.
Mistake to avoid: Treating a limited data set as fully de-identified and releasing it without a data use agreement.
Reference: HHS Summary of the HIPAA Privacy Rule
References and further reading
Source links checked on Oct 2, 2026.