Writing a Diagnosis for Rat Poisoning (Rodenticide Toxicity)

Step 1: Identify the Type of Rodenticide

Step 2: History-Taking (Key Diagnostic Foundation)

• Exposure history: What product was ingested? Obtain the packaging if possible.
• Route: Ingestion, inhalation (zinc/aluminum phosphide release phosphine gas), or dermal.
• Time of ingestion: Anticoagulant effects are delayed 12-48 hours; bromethalin effects may be delayed several days.
• Intentional vs. accidental: Children and depressed patients may not volunteer this information. An unexplained coagulopathy or bleeding should raise suspicion.
• Amount: A single mouthful of a warfarin rodenticide in a child is typically insignificant. Intentional large or repeated ingestions of superwarfarins are serious.
• Contact your regional Poison Control Center or medical toxicologist early.

Step 3: Clinical Presentation by Type

Anticoagulant / Superwarfarin Rodenticides (most common - ~80% of US exposures)

• Onset: 12-48 hours post-ingestion (superwarfarins can cause anticoagulation for weeks to months due to the ~120-day half-life of brodifacoum)
• Bleeding manifestations: epistaxis, gingival bleeding, hematemesis, melena, hematuria, hematochezia, hemoptysis, ecchymosis
• Anemia, lethargy, weakness, dyspnea (from internal hemorrhage)
• In severe cases: hemothorax, hemoabdomen, intracranial hemorrhage, hypovolemic shock

Bromethalin (neurotoxic)

• High-dose: severe tremors, hyperexcitability, seizures within 2-24 hours
• Low-dose: delayed onset (several days), hind-limb ataxia, paresis, can progress to seizures
• No antidote

Cholecalciferol (Vitamin D3)

• Signs delayed 36-48 hours: anorexia, weakness, vomiting, polyuria/polydipsia
• Progresses to acute renal failure within 2-3 days
• Hypercalcemia + hyperphosphatemia + soft-tissue mineralization

Zinc/Aluminum Phosphide

• GI symptoms, pulmonary edema, hypotension, anemia
• Metabolic acidosis, hypokalemia, hypoglycemia, elevated troponin (cardiac myocyte damage)

Arsenic

• Nausea/vomiting, bloody diarrhea, muscle cramps, dysarthria, QT prolongation, cardiovascular collapse, late peripheral neuropathy

Step 4: Diagnostic Workup

For ALL cases:

• History + packaging identification (most important)
• Basic metabolic panel / comprehensive metabolic panel: electrolytes, BUN, creatinine, glucose, liver enzymes, calcium, phosphate
• CBC: anemia (anticoagulants, phosphides), thrombocytopenia (phosphides)
• Chest and abdominal X-rays: radiopaque rodenticides (barium, arsenic, thallium) may be visible; also assess for hemothorax, hemoabdomen (loss of serosal detail)

For anticoagulant/superwarfarin poisoning:

• Prothrombin time (PT) / INR - the primary test; PT elevates first, then aPTT
  • Baseline PT/INR on presentation
  • Repeat at 24 and 48 hours after ingestion (if asymptomatic and vitamin K1 not yet given)
  • If vitamin K1 has been administered, recheck PT 2-3 days after treatment
• aPTT - elevates shortly after PT; both are typically elevated by the time bleeding is clinically apparent
• INR >2.0 warrants treatment with vitamin K1 (phytonadione)
• Superwarfarin is NOT detected by standard warfarin assays; specific serum assays are available at reference laboratories

For bromethalin:

• No reliable ante-mortem test; definitive diagnosis is post-mortem via identification of toxic metabolite desmethylbromethalin in brain or fat tissue

For cholecalciferol:

• Serum calcium (hypercalcemia) and serum phosphate (hyperphosphatemia)
• BUN/creatinine for renal function

For phosphides:

• ECG: QTc prolongation
• Serum lactate / ABG: anion-gap metabolic acidosis
• Troponin: cardiac myocyte damage
• Serum lipase: elevated with pyriminil

For strychnine:

• Creatine phosphokinase (CPK): elevated due to muscle damage from severe convulsions

For thallium:

• 24-hour urine thallium: most reliable method; >10-20 mg/L = severe poisoning
• Serum thallium: normal <2 mcg/L; whole blood >100 mcg/dL = poisoning
• Hair analysis for chronic exposure

Step 5: Differential Diagnosis

• Disseminated intravascular coagulation (DIC)
• Acute viral gastroenteritis
• C. difficile infection
• Acute hepatitis
• Organophosphate/carbamate toxicity
• Intracranial hemorrhage or stroke
• Rattlesnake bite (coagulopathy)
• Alcohol or opioid withdrawal
• Diabetic ketoacidosis
• Epilepsy

Writing the Formal Diagnosis Statement

Diagnosis: Rodenticide (anticoagulant/superwarfarin) toxicity Supporting evidence: History of [known/suspected] exposure to [product name/type], presenting with [epistaxis/bleeding/coagulopathy], INR [X.X], PT [X] seconds, aPTT [X] seconds. Anticoagulant rodenticide toxicity confirmed/suspected.

Diagnosis: Rodenticide toxicity - bromethalin type Supporting evidence: History of exposure, onset of generalized tremors, ataxia, and seizures [X hours] post-ingestion. No alternative cause identified.

• Tintinalli's Emergency Medicine: A Comprehensive Study Guide, p. 1348-1349
• StatPearls: Rodenticide Toxicity (NBK554428)
• Merck Veterinary Manual: Anticoagulant Rodenticide Poisoning

Writing a Clinical Diagnosis for Rat Poisoning (Medical Documentation)

1. The Diagnostic Statement Format

[Specific rodenticide class] toxicity / poisoning by [route of exposure], [intentional / accidental / unknown intent]

Anticoagulant rodenticide (superwarfarin) poisoning, oral ingestion, intentional

Rodenticide toxicity, type unspecified, accidental ingestion

Brodifacoum-associated coagulopathy with active hemorrhage

Rodenticide poisoning, suspected - anticoagulant type (pending confirmatory assay)

2. Required Elements to Support the Diagnosis

A. History (the most important component)

• Known or suspected exposure to a rodenticide (brand name and packaging if available)
• Time of ingestion (onset of anticoagulant effects: 12-48 hours; bromethalin: 2-24 hours or delayed days; cholecalciferol: 36-48 hours)
• Route (oral ingestion is most common; inhalation for phosphides)
• Intent: accidental vs. intentional
• Amount ingested if known
• Prior use of anticoagulants or bleeding disorders

"The diagnosis may not be readily apparent. Some patients may not report an intentional ingestion. Small children and depressed patients with an unexplained coagulopathy or bleeding should raise suspicion of superwarfarin poisoning."

• Tintinalli's Emergency Medicine, p. 1348

B. Physical Examination Findings

• Epistaxis, gingival bleeding, hemoptysis
• Hematuria, melena, hematochezia, hematemesis
• Ecchymosis, hematoma
• Pallor, tachycardia (from anemia/blood loss)
• Signs of hemothorax (decreased breath sounds, dyspnea)
• Abdominal distension (hemoperitoneum)

• Tremors, hyperexcitability
• Ataxia, paresis (hind-limb predominant)
• Seizures

• Polyuria, polydipsia, dehydration
• Weakness, vomiting

• Severe GI symptoms, pulmonary edema
• Altered mental status, cardiovascular collapse

C. Laboratory and Diagnostic Tests

Key note: Superwarfarin is NOT detected by standard warfarin assays. Specific serum assays must be ordered from a reference laboratory. Document this distinction in your note.

For large exposures: INR must be checked at a minimum of 2 days after ingestion before concluding no toxicity. - Rosen's Emergency Medicine

D. Differential Diagnosis (document what was ruled out)

• Disseminated intravascular coagulation (DIC)
• Hepatic failure (liver synthetic dysfunction)
• Hemophilia or other inherited coagulopathy
• Intracranial hemorrhage (non-toxic)
• Organophosphate / carbamate toxicity
• Rattlesnake envenomation
• C. difficile infection (if GI dominant)
• Alcohol-related coagulopathy

3. ICD-10 Codes (for the chart)

4. Sample Chart Diagnosis Entry

• History of [known / suspected] ingestion of [product name] on [date], [accidental / intentional]
• Presenting symptoms: [epistaxis / ecchymosis / hematuria / hemoptysis / other bleeding]
• INR: [X.X] (baseline / repeat at 24h / repeat at 48h)
• PT: [X] sec; aPTT: [X] sec
• CBC: Hgb [X], Hct [X], platelets [X]
• Imaging: [CXR findings / abdominal XR findings]
• Specific superwarfarin assay: [pending / positive for brodifacoum / not performed]
• Poison Control Center contacted: [Yes / No], case number [#####]

5. Key Documentation Pitfalls to Avoid

• Do not write a diagnosis of "rat poisoning" alone - specify the class (anticoagulant, neurotoxic, etc.) or note it as "type unspecified pending workup"
• Do not discharge based on a normal INR at presentation alone; anticoagulant effects are delayed 12-48 hours and must be rechecked
• Always document Poison Control Center (1-800-222-1222 in the US) consultation in the chart
• Note whether the ingestion was intentional - this has legal, psychiatric, and clinical implications
• If a child under 6 had a single unintentional exposure to a superwarfarin product, document that this age group has an extremely low rate of clinical toxicity and that serial INR monitoring rather than immediate treatment is appropriate

• Tintinalli's Emergency Medicine: A Comprehensive Study Guide, pp. 1348-1349
• Rosen's Emergency Medicine: Concepts and Clinical Practice (Pesticide/Rodenticide chapter)
• StatPearls: Rodenticide Toxicity