ICD-10 code A35: Other Tetanus

Key Takeaways

ICD-10 Code A35 classifies Other Tetanus, including cephalic, localized, and tetanus NOS, caused by Clostridium tetani toxin.

A35 excludes tetanus neonatorum (A33) and obstetrical tetanus (A34) via a Type 1 Excludes note – never code these together.

Documentation must specify the clinical form and confirm the absence of neonatal or obstetrical context before assigning A35.

For a tetanus vaccination or booster encounter (not active disease), code Z23 (encounter for immunization) – not A35.

Pabau’s claims management software helps clinics submit A35-coded encounters with accurate supporting documentation and reduce denials.

ICD-10 Code A35 is the billable diagnosis code for Other Tetanus – every form of active tetanus that is neither neonatal (A33) nor obstetrical (A34). It is the ICD-10 code for tetanus that applies to the vast majority of adult presentations seen in emergency and general practice settings. The distinction coders trip on is active disease versus prevention: A35 codes confirmed tetanus, while a tetanus vaccination or booster encounter is coded to Z23, not A35.

A35 sits within chapter A00-B99 (Certain Infectious and Parasitic Diseases), sub-block A30-A49 (Other Bacterial Diseases). It is a billable, specific diagnosis code valid for fiscal year 2026 reimbursement. This reference covers the code definition, applicable-to synonyms, Type 1 Excludes restrictions, related codes across the tetanus family, clinical context, documentation requirements for billing, and when to code a tetanus vaccination or booster to Z23 instead.

ICD-10 Code A35: Definition and clinical description

ICD-10 Code A35 is the diagnosis code for Other Tetanus. “Other” here means any tetanus presentation that is neither neonatal (A33) nor obstetrical (A34). The underlying pathogen is Clostridium tetani, a gram-positive, spore-forming anaerobic bacterium whose toxin, tetanospasmin, blocks inhibitory neurotransmitter release at the spinal cord and brainstem.

The result is sustained muscle rigidity and spasm. Trismus (lockjaw) is the hallmark presentation, often accompanied by risus sardonicus, opisthotonus, and, in severe cases, autonomic instability with cardiovascular fluctuations.

ICD-10 Code A35 is confirmed as billable for 2026 by both the CDC/NCHS ICD-10-CM web tool and the CMS ICD-10 codes page. No additional code is required to make A35 reportable.

Code details at a glance

Applicable-to terms and synonyms for A35

The ICD-10-CM tabular list includes an “Applicable To” note under A35 that functions as a scope statement. These are not additional codes – they confirm that the following clinical descriptions map to A35.

• Tetanus NOS – NOS stands for “Not Otherwise Specified.” Use this when documentation confirms tetanus but does not distinguish a specific anatomical or clinical form.
• Cephalic tetanus – A localized variant where the toxin travels to the brainstem via cranial nerves, typically following head or face wounds. Presents with cranial nerve palsies alongside spasm.
• Localized tetanus – Muscle rigidity confined to the region near the wound entry site. Less severe than generalized tetanus; often precedes a generalized presentation if untreated.
• Autonomic disorder due to tetanus – Autonomic instability caused by tetanospasmin affecting the sympathetic nervous system. Presents with labile blood pressure, tachycardia, diaphoresis, and hyperthermia.
• Generalized tetanus – The most common form. Descending or ascending rigidity affecting all muscle groups, trismus, and full-body spasm triggered by minor stimuli.

All five presentations above share the same root etiology – tetanospasmin released by Clostridium tetani – and all are correctly coded as ICD-10 Code A35 in the absence of neonatal or obstetrical context. For ICD-10 diagnostic code reference articles covering other neurological and infectious conditions, the same applicable-to logic applies: the synonym list defines the code’s clinical scope, not separate sub-codes.

Type 1 Excludes note: A35 vs A33 and A34

ICD-10 Code A35 carries a Type 1 Excludes note for two codes. Type 1 Excludes means “not coded here” – these conditions are mutually exclusive with A35 and must never be coded together on the same claim.

The distinction is clinical, not administrative. A34 requires the physician to document a clear obstetrical context – delivery, abortion, or postpartum wound. A33 requires neonatal presentation with umbilical involvement. Any tetanus case that does not meet those specific criteria defaults to ICD-10 Code A35. Applying A35 when A33 or A34 is clinically indicated – or vice versa – constitutes a coding error that may trigger medical necessity reviews.

Clinical overview of tetanus and A35 coding context

Tetanus is a toxin-mediated disease, not a direct bacterial infection of tissue. Clostridium tetani spores enter through wounds – puncture wounds, lacerations, burns, crush injuries, or even minor abrasions – and germinate under anaerobic conditions. The resulting exotoxin tetanospasmin travels via motor neurons to the central nervous system.

According to the WHO ICD-10 browser, tetanus is classified within the Certain Infectious and Parasitic Diseases chapter, reflecting its pathogen-driven origin. The CDC/NCHS ICD-10-CM classification maintains this structure in the US clinical modification, with A35 as the catch-all for non-neonatal, non-obstetrical presentations.

Clinical forms covered by A35

Generalized tetanus accounts for roughly 80% of reported cases. It begins with trismus (jaw stiffness), progresses to risus sardonicus (sustained facial spasm), and may advance to opisthotonus (arched-back rigidity). Autonomic dysfunction emerges in severe cases, adding cardiovascular instability to the spasm burden. All these presentations code to A35.

Cephalic tetanus is a less common but clinically distinct form. Wound entry is on the head or face – sometimes following otitis media with Clostridium tetani contamination. Cranial nerve involvement, especially CN VII palsy, distinguishes it from generalized tetanus. Despite the anatomical specificity, it still maps to ICD-10 Code A35.

Localized tetanus causes rigidity near the wound site only. It can persist for weeks and carries a lower mortality than generalized tetanus. From a coding standpoint, it is indistinguishable from other A35 presentations – the specificity lives in the clinical notes, not the code itself.

Effective patient record management is essential here. The clinical note must capture the form of tetanus, the wound source, the patient’s vaccination history, and the absence of neonatal or obstetrical context – all before a coder can confidently assign A35 rather than A33 or A34. Gaps in that documentation create coding ambiguity that delays reimbursement.

Documentation requirements for ICD-10 Code A35

Payers reviewing an A35-coded claim will look for clinical evidence that supports the diagnosis and confirms the Type 1 Excludes restrictions are met. Incomplete documentation is the primary driver of A35 claim queries.

The note should capture four elements before the coder assigns A35:

1. Wound history – entry site, mechanism (puncture, laceration, burn), and environment of injury (outdoor, soil contact, animal bite)
2. Patient age and reproductive context – confirms the absence of neonatal status and, for female patients of childbearing age, rules out obstetrical context
3. Clinical form – generalized, localized, cephalic, or autonomic tetanus, supported by the specific signs documented (trismus, cranial nerve involvement, autonomic instability)
4. Vaccination status – whether prior Td/Tdap immunization occurred and when, which informs clinical management decisions documented in the record

Consistent ICD-10 coding documentation standards across all infectious disease encounters reduce the risk of payer audits. Practices using digital clinical forms can build structured intake templates that prompt clinicians to capture wound history, vaccination status, and clinical presentation systematically – reducing documentation gaps before the note reaches the coder.

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Billing and coding guidelines for A35

A35 is a primary diagnosis code. It can stand alone on a claim when tetanus is the principal reason for the encounter. In inpatient settings where the ICD-10-PCS procedure coding system applies alongside ICD-10-CM, A35 drives the principal diagnosis assignment and may influence DRG grouping under MDC 18 (Infectious and Parasitic Diseases).

CPT codes commonly billed with A35

Tetanus management in outpatient or emergency settings typically generates several supporting CPT codes alongside the A35 diagnosis. Common pairings include:

• 99213-99215 – Office or other outpatient visit (E/M level depending on complexity)
• 90714 – Td (tetanus and diphtheria toxoids) vaccine administration, if prophylaxis is updated at the encounter
• 90471 – Immunization administration for each injection
• 86280 – Tetanus antitoxin (if tetanus immune globulin (TIG) is administered and separately reportable)
• 99291 – Critical care, first 30-74 minutes (for severe generalized tetanus with autonomic instability)

Verify payer-specific coverage policies before appending immunization CPT codes to A35. Some payers bundle prophylactic administration within the E/M visit when the wound evaluation is the primary purpose of the encounter.

Sequencing guidance

When tetanus is the principal diagnosis driving the admission or encounter, A35 is sequenced first. If the patient also has a documented wound requiring separate coding (for example, a traumatic laceration that introduced Clostridium tetani), the wound code is a secondary diagnosis – the infectious condition (A35) takes the principal position because it is the condition established after study to be chiefly responsible for the episode of care.

Practices running claims management software can flag diagnosis sequencing errors before submission. The system can prompt coders when a principal infectious disease code is sequenced behind a symptom code, which is a common denial trigger for A35 encounters where trismus (R68.84) was coded first instead of A35.

For HIPAA-compliant billing workflows, the claim must match the documentation exactly. A35 on the claim requires tetanus confirmed in the clinical note – not just suspected or ruled out.

Related codes in the A35 family

Understanding where A35 sits in the broader tetanus and infectious disease code family helps coders select the right code on first pass. For clinics managing infectious disease encounters alongside other diagnostic code categories, the same discipline applies – as seen in ICD-10 codes for acute neurological conditions, where precise family navigation prevents misassignment between closely related codes.

Z23 is particularly useful in wound care settings where a patient presents for laceration repair and receives a tetanus booster prophylactically. The encounter reason is wound care – not active tetanus – so A35 would be incorrect. Z23 is the appropriate secondary code alongside the wound diagnosis.

Tetanus vaccination and prophylaxis coding: A35 vs Z23

The most common A35 misassignment is using it for a patient who came in for a shot, not a disease. A35 is reserved for confirmed, active tetanus. When the encounter is prophylactic – a routine tetanus vaccination, a booster, or a post-injury shot with no active infection – the reason for the visit is Z23 (encounter for immunization), and A35 does not belong on the claim.

That splits the tetanus vaccine code question into two parts: the ICD-10 diagnosis (why the patient is here) and the CPT codes (the vaccine product and its administration).

• Z23 – Encounter for immunization. This is the ICD-10 code for a tetanus vaccine or booster visit when prevention, not disease, is the purpose of the encounter.
• Vaccine product code – the tetanus vaccine code depends on the formulation: 90715 for Tdap (tetanus, diphtheria, acellular pertussis) or 90714 for Td (tetanus and diphtheria toxoids), paired with administration code 90471.
• Injury-driven booster – when a wound prompts the booster, the injury or wound code is the first-listed reason for the encounter and Z23 follows it. The administration of a tetanus vaccine maps to A35 only when the record documents active tetanus alongside it.

Setting up the prophylactic visit and the active-disease encounter as separate intake templates keeps A35 off vaccination claims. Practices using digital clinical forms can route a booster encounter to the immunization pathway automatically, so the coder never has to reverse a defaulted diagnosis before submission.

Conclusion

Most adult tetanus presentations in clinical practice fall under ICD-10 Code A35. The code’s scope covers every form of tetanus that is not neonatal or obstetrical, including cephalic, localized, generalized, and autonomic tetanus variants. The Type 1 Excludes note for A33 and A34 makes the code boundaries clear – when in doubt, check patient age and obstetrical context before assigning.

Accurate A35 coding depends on clinical notes that document wound history, patient demographics, the specific presentation, and vaccination status. Practices using Pabau’s claims management software can build the documentation and submission workflows that prevent the sequencing and context errors that drive A35 denials. Book a demo to see how Pabau supports infectious disease coding accuracy across your practice.

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