Toxicological Screening and Diagnosis

Initial Assessment in Poisoning - Spotting Poison's Play

• Airway, Breathing, Circulation (ABCs): Secure, ventilate, circulate. Utmost priority!
• History (AMPLE & Poisoning Specific):
  • 📌 Allergies, Medications, Past medical Hx, Last meal, Events.
  • Substance, Dose, Time, Route (📌 SDTR).
  • Intent, symptoms onset, co-ingestants.
• Examination (Head-to-Toe):
  • Vitals (HR, BP, RR, T, SpO2).
  • Pupils (size, reactivity: miosis/mydriasis).
  • Skin (color, temp, moisture, marks, diaphoresis).
  • Odors (breath, body fluids - e.g., garlic, almonds).
  • Neuro status (GCS, seizures, reflexes).
  • Recognize Toxidromes (e.g., Opioid, Cholinergic, Anticholinergic, Sympathomimetic, Sedative-hypnotic).
• Initial Stabilization:
  • Oxygen, IV access, cardiac monitoring.
  • Correct immediate life threats (hypoxia, hypotension, hypoglycemia, seizures, arrhythmias).

⭐ Toxidrome recognition is key to guiding empirical treatment before definitive lab results.

Toxicological Screening Methods - Culprit Catchers

• Purpose: Identify toxins, guide antidote use, medico-legal.
• Common Samples:
  • Urine: Preferred for screening (wide window).
  • Blood (Serum/Plasma): For quantification, correlates with acute toxicity.
  • Gastric Aspirate: If recent, large ingestion.
• Key Techniques:
  • Immunoassays (e.g., ELISA, EMIT): Rapid, qualitative; common for drugs of abuse (DOA).
  • Chromatography:
    • GC-MS (Gas Chromatography-Mass Spectrometry): Gold standard for many volatiles; confirmatory.
    • HPLC (High-Performance Liquid Chromatography): For non-volatile, thermolabile substances.
  • Atomic Absorption Spectroscopy: For heavy metals.
• Considerations:
  • Screening panels detect common toxins only.
  • False positives/negatives possible. Clinical correlation is paramount.

⭐ Urine drug screens often detect metabolites, not parent drug; window varies (e.g., cannabis weeks, cocaine days).

Key Toxidromes - Symptom Signposts

Pattern recognition aids rapid diagnosis.

• Opioid:
  • ↓LOC, ↓RR, miosis (pinpoint pupils)
  • Hypotension, bradycardia, hypothermia
• Sympathomimetic:
  • Agitation, mydriasis
  • Tachycardia, hypertension, hyperthermia, diaphoresis
  • Seizures
• Anticholinergic:
  • "Mad as a hatter" (delirium)
  • "Blind as a bat" (mydriasis)
  • "Red as a beet" (flushed skin)
  • "Hot as a hare" (hyperthermia)
  • "Dry as a bone" (dry mucous membranes, urinary retention)
  • Tachycardia
• Cholinergic:
  • Muscarinic: 📌 SLUDGEM (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis, Miosis)
  • Nicotinic: Weakness, fasciculations
  • Killer B's: Bradycardia, Bronchorrhea, Bronchospasm
• Sedative-Hypnotic:
  • ↓LOC, slurred speech, ataxia
  • Respiratory depression (esp. barbiturates)
• Serotonin Syndrome:
  • Mental status changes (agitation)
  • Autonomic hyperactivity (tachycardia, hyperthermia)
  • Neuromuscular: Clonus, hyperreflexia (esp. lower limbs)

⭐ Mydriasis is seen in sympathomimetic and anticholinergic toxidromes, while miosis is characteristic of opioid and cholinergic (organophosphate) poisoning.

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Ancillary Labs & Tox Screen Limits - Deeper Dive Dx

• Key Ancillary Labs:
  • ABG:
    • Anion Gap (AG): $AG = (Na^+) - (Cl^- + HCO_3^-)$. Normal: 8-12 mEq/L.
      • 📌 MUDPILES for ↑AG.
    • Osmolal Gap (OG): $OG = Measured Osmolality - Calculated Osmolality$. Normal < 10-15 mOsm/kg.
      • ↑ in toxic alcohols (e.g., methanol, ethylene glycol).
  • ECG: QRS duration (e.g., TCAs), QT interval (e.g., antipsychotics).
  • Electrolytes (K+, Ca2+), LFTs, RFTs, Glucose.
• Toxicology Screen Limitations:
  • Not comprehensive; many drugs missed (e.g., synthetic opioids, novel psychoactive substances, many cardiovascular drugs).
  • Primarily qualitative; concentration not typically given.
  • Turnaround time often slow, may not guide emergency care.
  • False positives/negatives common.

    ⭐ Many common drugs like beta-blockers, calcium channel blockers, and digoxin are NOT detected on standard urine toxicology screens.

  • Clinical picture & specific assays guide management, not just broad screen.

High‑Yield Points - ⚡ Biggest Takeaways

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