ICD-10 code B79: Trichuriasis diagnosis, billable status, and coding guidance

Key Takeaways

ICD-10 Code B79 is a billable ICD-10-CM diagnosis code for trichuriasis (whipworm infection), valid for reimbursement claims with dates of service from October 1, 2025 onward.

B79 maps to MS-DRG 391 (with MCC) and MS-DRG 392 (without MCC) under the Esophagitis, gastroenteritis and miscellaneous digestive disorders groupings.

Coders must distinguish B79 from adjacent helminthiasis codes B77 through B83; using B82 (unspecified intestinal parasitism) when a confirmed whipworm diagnosis is documented is a common and avoidable error.

Pabau’s claims management software supports accurate ICD-10-CM code submission and streamlined documentation workflows for practices managing parasitic infection claims.

ICD-10 Code B79, the designated code for trichuriasis, sits within a tightly grouped range of intestinal parasite codes where a single digit of difference separates a specific, billable diagnosis from an unspecified one. This reference covers the billable status, MS-DRG groupings, adjacent codes, and documentation requirements coders and clinicians need for accurate B79 claims.

Trichuriasis is caused by Trichuris trichiura, commonly called whipworm. It ranks among the most prevalent soil-transmitted helminthiases globally, yet coding accuracy for this diagnosis remains inconsistently applied in US clinical settings. Coders working with ICD-10-CM diagnostic coding across infectious disease specialties and primary care will find this reference useful for both claim preparation and internal auditing.

ICD-10 Code B79: Definition and clinical description

ICD-10 Code B79 designates trichuriasis as a specific, billable diagnosis under the ICD-10-CM classification. The code sits within Chapter 1 of ICD-10-CM (Certain infectious and parasitic diseases), under the subcategory B65-B83 Helminthiases. According to the CDC/NCHS ICD-10-CM web tool, B79 is a valid leaf-node code requiring no further specification.

Trichuriasis results from infection by Trichuris trichiura, a roundworm that colonizes the large intestine. The adult worm embeds its anterior end into the intestinal mucosa, causing symptoms that range from asymptomatic carriage through to chronic diarrhea, rectal prolapse, and growth stunting in children with heavy worm burdens.

• Full code description: Trichuriasis
• Code system: ICD-10-CM (International Classification of Diseases, 10th Revision, Clinical Modification)
• Code category: B65-B83 Helminthiases
• Parent block: A00-B99 Certain infectious and parasitic diseases
• Billable/specific: Yes, leaf-node code
• Current edition: Valid and unchanged in FY2026 (effective October 1, 2025)
• Synonyms: Infection by Trichuris trichiura; infection by Trichuris globulosa; infection by Trichuris ovis; infection by Trichuris suis

The synonym entries reflect that B79 encodes infections by multiple Trichuris species, not only the human-specific T. trichiura. This matters when documentation references veterinary or zoonotic exposure contexts, particularly in agricultural or rural practice settings.

Billable status and reimbursement context

B79 is a fully billable ICD-10-CM code. Billable status means it can serve as the principal or secondary diagnosis on a claim and is sufficient justification for admission to an acute care hospital when used as the principal diagnosis. The CMS ICD-10 codes page confirms the code is included in the FY2026 tabular list without any deletion, revision, or billable-status change.

Practices using claims management software should confirm their system’s ICD-10 code library reflects the FY2026 edition (effective October 1, 2025). Code validity is tied to the date of service, not the claim submission date.

Key billing facts for B79

• Valid as principal diagnosis on inpatient or outpatient claims
• Valid as secondary diagnosis when trichuriasis is a complicating condition
• No Type 1 Excludes or Type 2 Excludes notes apply to B79 directly
• No mandatory sequencing rules require B79 to follow another code
• HIPAA mandates use of valid ICD-10-CM codes on all electronic claims; B79 meets this requirement

Payer-specific coverage policies for trichuriasis treatment (mebendazole, albendazole) may vary. Always verify individual payer LCD/NCD requirements before submitting B79 claims for antiparasitic drug reimbursement.

MS-DRG groupings for ICD-10 Code B79

Under MS-DRG v43.0 (FY2026), B79 groups to two possible DRGs depending on the presence or absence of a major complication or comorbidity (MCC). Correct ICD-10-CM code selection at the principal diagnosis level directly determines which DRG fires, affecting inpatient reimbursement amounts.

The DRG split at the MCC level underscores why complete documentation matters. A patient admitted with severe trichuriasis-related anemia or rectal prolapse may have qualifying MCC diagnoses coded alongside B79. Incomplete secondary diagnosis capture could cause a case to group to DRG 392 when DRG 391 is clinically supported.

MS-DRG assignments are updated annually on October 1. Verify the current version applies for your claim’s date of service, particularly for claims spanning fiscal year boundaries.

Adjacent helminthiasis codes and differential coding

B79 does not exist in isolation. It sits within a tightly grouped block of intestinal helminthiasis codes, and the diagnostic workup for one parasitic infection often reveals another. Coders should review the following adjacent codes when the clinical record documents multiple parasitic findings or when the specific organism is unclear.

The most consequential distinction for coders is between B79 and B82. B82 (unspecified intestinal parasitism) should never be used when lab results or endoscopy findings confirm Trichuris species. Using B82 when B79 is supported by the clinical record is a specificity error that payers can flag during audit.

For guidance on coding for complex, comorbid diagnoses where multiple concurrent conditions appear in the record, the same specificity principle applies: always code to the highest level of detail the documentation supports.

Polyparasitism (co-infection with multiple helminths) is common in endemic regions. When the stool ova and parasites (O&P) test confirms both Trichuris trichiura and Ascaris lumbricoides, for example, both B79 and B77 may be assigned on the same claim, sequenced according to the principal reason for the encounter.

Clinical context: diagnosis, treatment, and coding implications

Trichuriasis is diagnosed primarily through stool microscopy. The O&P (ova and parasites) examination identifies the characteristic barrel-shaped eggs of Trichuris trichiura. Colonoscopy occasionally reveals adult worms in the cecum and ascending colon when performed for other indications.

Treatment follows WHO-recommended antiparasitic protocols. Mebendazole 500 mg (single dose) or albendazole 400 mg (single dose) are first-line options. A follow-up O&P test at two to four weeks post-treatment is standard practice to confirm clearance, particularly for heavy worm burdens.

Practices supporting functional medicine software workflows, where parasitic infection screening is more commonly integrated into comprehensive protocols, will benefit from structured documentation templates that capture organism confirmation, worm burden assessment, and treatment response.

Coding implications of clinical severity

Light infections are typically asymptomatic and may be incidental findings. Heavy infections produce a distinct clinical syndrome: chronic mucoid diarrhea, iron-deficiency anemia, and, in children, Trichuris dysentery syndrome with rectal prolapse. These complications may generate additional ICD-10-CM codes alongside B79.

• Iron-deficiency anemia secondary to trichuriasis: Code D50.9 as an additional diagnosis; sequences after B79 unless anemia drives the encounter
• Rectal prolapse: Code K62.3 as an additional diagnosis when documented and directly attributed to heavy worm burden
• Growth stunting / failure to thrive (pediatric): Code R62.50 or R62.51 as applicable when documented in pediatric cases
• Protein-energy malnutrition: Code from E40-E46 range when clinician documents nutritional impact

Supporting patient compliance workflows for follow-up O&P testing is also relevant here. Practices that track follow-up visit completion can reduce the risk of untreated persistent infection, which creates a pattern of repeat B79 claims that payers may query.

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Documentation requirements for ICD-10 Code B79 claims

A B79 claim that fails payer review almost always fails for one reason: the documentation does not explicitly confirm Trichuris trichiura infection. Coders cannot assign B79 based on clinical suspicion, symptom presentation, or empiric treatment alone. The record must include documented evidence of the organism.

• Laboratory confirmation: Stool O&P microscopy report identifying Trichuris eggs or adult worms
• Endoscopic confirmation: Colonoscopy or sigmoidoscopy report documenting adult whipworms in situ
• Clinician attestation: Physician or qualified provider documentation of trichuriasis diagnosis in the encounter note
• Treatment record: Prescription or administration of mebendazole or albendazole supports medical necessity
• Travel and exposure history: Supports clinical context for endemic exposure; not required for billing but strengthens audit defensibility

Practices should ensure that digital intake forms capture travel history and gastrointestinal symptom duration as part of the initial clinical workup. This creates an auditable trail connecting patient history to diagnostic workup to confirmed diagnosis. When combined with structured medical records management, each element of the diagnostic pathway is retrievable for retrospective audit review.

Maintaining HIPAA compliance for medical offices extends to how diagnostic documentation is stored and retrieved. Electronic records that log who accessed or amended a record, with timestamps, provide the audit trail required under HIPAA’s security rule. This is especially relevant when B79 claims are selected for post-payment review.

Common documentation errors to avoid

• Coding B82 instead of B79: The unspecified code is only appropriate when no organism is confirmed. If the O&P test is positive for Trichuris, B79 is the correct code.
• Missing laboratory reference: The encounter note should reference the lab report date and result. A diagnosis of “trichuriasis” without a supporting lab reference invites query.
• Incorrect principal diagnosis sequencing: When the patient presents with anemia and trichuriasis is the cause, B79 sequences first. When the patient presents for a routine check and trichuriasis is found incidentally, the reason for the encounter sequences first.
• Outdated code validation: Confirm the code remains valid for the date of service. B79 is unchanged in FY2026, but code validity must be verified annually against the October 1 update.

Coding guidelines and regulatory context

B79 falls under the ICD-10-CM Official Guidelines for Coding and Reporting, maintained jointly by the Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS). The WHO’s ICD-10 classification browser provides the international reference framework from which ICD-10-CM is derived, though the US clinical modification adds specificity not present in the base WHO edition.

HIPAA requires that all electronic claims use valid ICD-10-CM codes for covered transactions. B79 satisfies this requirement for the FY2026 code year. Practices managing compliance management workflows should document code validity verification as part of their billing quality assurance process, particularly when treating patient populations with endemic exposure backgrounds.

ICD-10-CM code structure notes

B79 is a single-code designation with no sub-codes. Unlike B77 (Ascariasis), which has sub-codes for intestinal complications (B77.0), pneumonia (B77.81), and other complications (B77.89), trichuriasis has no further subdivision in ICD-10-CM. The full clinical picture of trichuriasis, including any complications, is captured by adding appropriate secondary diagnosis codes rather than through code extensions.

The ICD List free lookup tool confirms this structure and lists the accepted synonyms for B79, which coders can use when clinician documentation uses alternative terminology (such as “whipworm infection” rather than “trichuriasis”). For commercial code verification across ICD-10-CM ranges, the AAPC Codify ICD-10-CM lookup also validates B79 as billable with its full descriptor.

Practices applying HIPAA-compliant clinical documentation practices across their organization should include ICD-10 code verification steps in their billing cycle standard operating procedures. Annual October 1 updates may introduce adjacent code changes in the B65-B83 range, even when B79 itself remains stable.

Conclusion

B79 is a straightforward, fully billable code when clinical documentation supports a confirmed Trichuris trichiura diagnosis. The most common failure points are defaulting to the unspecified B82 when specificity is available, missing secondary diagnosis capture for complications, and submitting claims without a laboratory confirmation reference in the encounter record.

Practices that manage infectious disease or global health patient populations benefit from structured documentation workflows that connect lab results, clinical notes, and billing codes in a single auditable record.

Pabau’s claims management software supports this end-to-end workflow, from intake through ICD-10 code submission. To see how Pabau handles clinical documentation and billing workflow for your practice, book a demo.

Continue your research

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Want to understand ICD-10 coding for other infectious disease diagnoses? ICD-10 coding for complex diagnoses covers specificity principles that apply across the ICD-10-CM code set.

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