ICD code T61.773S – Sequela of fish poisoning by assault

Key takeaways

T61.773S is the billable ICD-10-CM code for a late effect of other fish poisoning when the record shows another person caused it deliberately.

Code the residual condition first and T61.773S second, because the sequela code explains the cause rather than the reason for the visit.

Use 7th character S only after the acute poisoning has resolved, and keep A or D while treatment or recovery is still under way.

Ciguatera (T61.0-) and scombroid (T61.1-) have their own codes, and unknown intent defaults to accidental (T61.771S), not assault.

Pabau, practice management software with built-in claims tools, pre-fills claims from the patient record, offers ICD-10-CM and CPT code lookup, and checks required claim fields.

ICD-10 code T61.773S flags a late effect of fish poisoning by assault

ICD-10 code T61.773S is the billable ICD-10-CM code for other fish poisoning, assault, sequela. You report it when a patient still has a problem caused by fish that someone deliberately used to poison them. The acute episode must already be over.

Three details have to line up in the chart before the code fits. The fish can’t be ciguatera or scombroid, the intent has to be assault, and the visit has to be for a late effect. The table below pulls the reference data into one place.

Only the full seven characters make T61.773S billable

T61.773S is a seven-character code, and each step down the hierarchy narrows the meaning. The parent levels help you find the code, but none of them can go on a claim.

Submitting T61.77 or T61.773 in place of the full code is one of the quickest ways to earn a denial. Payers reject any diagnosis that stops short of its highest level of specificity.

Two characters decide whether T61.773S is the right fish poisoning code

The 6th character records intent, and the 7th records where the patient is in their care. The grid below shows how the two combine across the T61.77 subcategory, with T61.773S in the assault and sequela cell.

Assault only fits when the record says someone else caused it

Intent is where T61.773S goes wrong most quietly. The official guidelines say that when intent is unknown or unspecified, you code it as accidental. So T61.771S, not T61.773S, is the default for a late effect of other fish poisoning.

Assault needs documentation that another person deliberately poisoned the patient. A physician statement, a safeguarding note, or a police report named in the history can all support it. Undetermined intent (T61.774S) is only for records stating that intent can’t be established.

Here is how four common chart notes map to the intent character:

• “Ate spoiled fish at a restaurant”: accidental, so T61.771S.
• “Partner admits adding toxic fish to her meal”: assault, so T61.773S.
• “Ate fish she knew was toxic to harm herself”: intentional self-harm, so T61.772S.
• “Intent could not be determined after review”: undetermined, so T61.774S.

The 7th character tracks the patient’s care, not the calendar

With intent settled, the 7th character signals the type of encounter. Picking the wrong one is the other common denial trigger in this code family.

When S applies, the sequencing flips. The residual condition, such as neuropathy, fatigue or a GI complaint, goes first as the primary diagnosis. T61.773S follows as the cause. That catches out coders used to A and D encounters, where the poisoning code leads.

Neighboring codes that can pass for T61.773S at a glance

Before you settle on T61.773S, rule out the named fish poisonings and the lookalikes around it. Choosing the wrong sibling code is a documentation mismatch that auditors look for on retrospective review.

Scombroid or other fish: the species settles it

Scombroid poisoning (T61.1-) is histamine-driven. Poorly refrigerated fish builds up histamine, which triggers a flushing, allergy-like reaction. The documented species drives the code choice here, not the symptom pattern.

• T61.11XS applies when the physician documents tuna, mackerel, bonito, mahi-mahi, bluefish or another scombroid species as the source. It is the default intent, and T61.13XS replaces it only when assault is documented.
• T61.773S applies when the fish is neither scombroid nor ciguatera, or when the species is unknown but documented as “other fish” rather than seafood generically.
• Never assign a T61.1- code from the symptom pattern alone. You need the species or a physician statement about the toxin mechanism.

Fish allergy isn’t fish poisoning, and the codes differ

An IgE-mediated fish allergy doesn’t code to T61.773S. Allergic reactions have their own codes, such as T78.03- for anaphylaxis due to other fish or Z91.013 for a seafood allergy. The physician’s note has to separate an immune reaction from a direct toxic effect.

• Toxicity (T61.773S): the fish substance acts directly on the body. Anyone exposed to enough of it can react, with no prior sensitization.
• Allergy: an IgE-mediated immune response that needs prior sensitization. It codes to allergy categories, not T61.
• A patient with anaphylaxis after shellfish has an allergy. A patient with neurological symptoms weeks after eating an unidentified fish may have a toxic sequela.
• If the note says “allergic reaction to fish,” T61.773S is not supported until the physician clarifies the documentation.

What the physician’s note must say before you code T61.773S

Six details in the note decide whether a T61.773S claim survives payer review. If any one is missing, an auditor has grounds to deny.

• Explicit causal link: the note states that the current condition results from the prior fish poisoning. “Peripheral neuropathy secondary to prior fish toxin ingestion” meets the bar. “History of fish poisoning” alone does not.
• Resolved acute phase: the note confirms the acute episode has ended. Without it, you can’t justify S over A or D.
• Named residual condition: the specific late effect, such as fatigue or GI dysmotility, is named and coded as the primary diagnosis.
• Documented assault: the record says another person caused the poisoning on purpose. Without that, code the accidental default.
• Fish type or toxin, if known: a note that says “other fish” rather than naming a species supports T61.773S over a more specific code.
• Date or rough timeframe of the exposure: not always available, but payers may ask for it on complex sequela claims.

Supporting medical billing compliance at the documentation level is where sequela claims succeed or fail. A note that could describe either active poisoning or a late effect leaves the coder guessing. A physician query before submission stops the denial before it starts.

External cause codes belong to the first visit, not the sequela claim

The short answer is that a T61.773S sequela claim usually carries no Y92, Y93 or Y99 codes. Those codes describe the original event, and the guidelines tie them to the initial encounter.

• Place of occurrence (Y92.x): where the exposure happened, such as a home or a restaurant. It is reported once, at the initial encounter for treatment.
• Activity (Y93.x): what the patient was doing at the time. Activity codes are not used for poisonings or for sequela.
• External cause status (Y99.x): Y99.0 is civilian activity done for income or pay, and Y99.8 covers other statuses such as leisure. Status codes are not used for poisonings or sequela either.
• The poisoning itself: no separate external cause code is needed, because the T61 code already carries the intent.

If a payer edit asks for an external cause code on a sequela claim, check that payer’s written policy first. Adding Y codes the guidelines leave out can create a new problem instead of fixing one.

Following a T61.773S claim from the note to payment

So how does a sequela claim move in practice? Take a simplified example. A patient returns months after a coworker deliberately tainted her lunch with toxic fish. The acute illness resolved, but she still has persistent fatigue.

1. The physician documents the fatigue, links it to the prior fish poisoning, notes the assault, and confirms the acute phase has ended.
2. The coder lists the fatigue code first (R53.83, other fatigue), then adds T61.773S as the cause.
3. On the 837P or CMS-1500, the fatigue code takes diagnosis position A and T61.773S takes position B. The service line points to A first. Our guide to 837 files shows where each sits.
4. The claim scrubber or clearinghouse checks required fields, code validity and format before the claim goes out.
5. The payer adjudicates. An injury or assault diagnosis can prompt a coordination-of-benefits or accident questionnaire, so answer it quickly.
6. The remittance comes back as an 835 ERA. If the claim is denied, its CARC and RARC codes point you to the fix.

Why T61.773S claims get denied, and how to fix each one

T61.773S denials follow a predictable pattern, and most trace back to the chart or the claim order. The table maps each trigger to its fix. A clear denial management workflow before submission cuts the rework.

When a denial does arrive, the remittance tells you why. Look up the CARC in our list of medical billing denial codes, then match it to the fix above.

Before you submit: A quick T61.773S checklist

Run through these seven checks on every sequela claim before it leaves the practice:

• The note names the residual condition and links it to the prior fish poisoning.
• The note confirms the acute poisoning has resolved.
• The record documents assault, or you have switched to the accidental code.
• The fish is not ciguatera or scombroid, and the injury was not a venomous sting.
• The residual condition sits first on the claim, with T61.773S second.
• No Y92, Y93 or Y99 codes have been carried over from the initial encounter.
• Any open question has gone to the physician as a query before the claim goes out.

The official guidelines behind sequela coding for T61.773S

Two parts of the ICD-10-CM Official Guidelines govern this code. Section I.B.10 sets the general sequela rules, and Section I.C.19 covers 7th characters and toxic effects. Both shape clean claim submission for T61.773S.

• The sequela condition is coded first. The residual condition is the primary diagnosis. That is the opposite of acute poisoning coding, where the T code leads.
• The poisoning code with 7th character S is coded second. T61.773S shows the cause of the residual condition.
• No extra external cause code is needed for the poisoning. The T61 code already records intent, and the place code belongs to the initial encounter.
• Both codes go on the same claim. They are never split across visits.

The CMS ICD-10 coding page publishes the annual guidelines as a free PDF. Check these sections in the current fiscal year’s release, because the wording can shift in annual updates.

How payers treat T61.773S, and where the assault changes the bill

T61.773S meets ICD-10-CM specificity rules for Medicare and Medicaid, so it’s valid as a secondary diagnosis on a complete claim. Commercial acceptance still varies by plan and coverage policy.

• Medicare and Medicaid: no national coverage determination (NCD) excludes T61.773S. Even so, sequela documentation gets close attention on audit.
• Commercial payers: many run automated edits that flag a sequela code submitted in the first position.
• LCD applicability: a local coverage determination for the residual condition may call for extra documentation. T61.773S has no LCD of its own.
• Crime victim compensation: because the code records an assault, the patient may qualify for their state’s crime victim compensation program. These programs usually pay after insurance, so ask whether the patient has an open claim.

Seeing where these claims sit in your revenue cycle management helps you build checks that catch errors every time, not case by case. That is where claims software earns its place.

How claims software keeps sequela claims like T61.773S clean

In many practices, a sequela claim still depends on one coder remembering the sequencing rule. The diagnosis gets retyped from the note, the claim goes out, and the error surfaces weeks later as a denial.

Pabau’s claims management software pre-fills each claim from the patient record, so the diagnoses in the note carry straight onto the claim. Built-in ICD-10-CM and CPT code lookup helps your team find the full seven-character code. Required claim fields are checked before submission.

For US practices, Pabau submits claims through Claim.MD. That adds real-time eligibility checks, ERA posting and claim-status tracking, so a rejected T61.773S claim shows up the same day. Coding judgment, like intent and sequencing, stays with your coders and the checklist above.

Send cleaner sequela claims the first time

Pabau pre-fills claims from the patient record and checks required fields before submission. Through Claim.MD, it also runs real-time eligibility checks, posts ERAs and tracks claim status.

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Conclusion

T61.773S rewards coders who read the chart before they read the code list. Confirm the assault, confirm the acute phase has ended, and put the residual condition first. Get those three right and the claim has little left to trip over.

The trade-off is time. A physician query adds a day, while a denial and appeal can add weeks. Superbill preparation that captures the residual condition alongside T61.773S keeps those queries rare.

Once the claim is out, Pabau’s eligibility checks and claim-status tracking through Claim.MD show you where it stands. Book a demo to see how Pabau moves your sequela claims from the note to payment.

Continue your research

Need to understand how claim denials are categorized? Denial codes in medical billing explains CARC and RARC codes and how to match them to corrective action.

Want to streamline ICD-10 claim submission? Claim.MD clearinghouse overview covers how electronic clearinghouse submission reduces manual errors on ICD-10-CM claims.

Looking for guidance on the 837 electronic claim format? 837 file format guide walks through how ICD-10-CM codes are structured in EDI 837P submissions.

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