Paracetamol

Diagnostic Use

Patients exhibit variable sensitivity to the toxic effects of paracetamol, so the graph below only gives an indication of the likely effect. The minimum time for assessment of levels after ingestion of tablets or linctus is 4 hours. Specimens collected earlier than 4 hours may not indicate the peak serum concentration.
The time since ingestion must be provided with the request in order to assess whether level is toxic or nontoxic.
If patients are seen late (after 8 hours post-ingestion) treatment should not necessarily be delayed while awaiting serum concentration results.This graph below is based on one used by the National Poisons Centre (Dunedin, NZ)
The  time is hours since ingestion.
The units are umol/L
Patients with drug concentrations above the line should be treated.
Patients with risk factors for toxicity (e.g. alcoholism, enzyme inducing drugs, fasting) may need treatment if the drug concentration is above the dotted line.Jaundiced patients (bilirubin >300 umol/L) may show false-positive serum paracetamol results.

Paracetamol toxicity or N-acetycysteine can negatively interfere with lactate, urate, total cholesterol, HDL-cholesterol and triglyceride assays. Exercise caution in interpreting these results.

Reference Intervals

• Patients exhibit variable sensitivity to the toxic effects of paracetamol, so the graph below only gives an indication of the likely effect. The minimum time for assessment of levels after ingestion of tablets or linctus is 4 hours. Specimens collected earlier than 4 hours may not indicate the peak serum concentration.
• The time since ingestion must be provided with the request in order to assess whether level is toxic or nontoxic.
• If patients are seen late (after 8 hours post-ingestion) treatment should not necessarily be delayed while awaiting serum concentration results.This graph below is based on one used by the National Poisons Centre (Dunedin, NZ)
• The  time is hours since ingestion.
• The units are umol/L
• Patients with drug concentrations above the line should be treated.
• Patients with risk factors for toxicity (e.g. alcoholism, enzyme inducing drugs, fasting) may need treatment if the drug concentration is above the dotted line.Jaundiced patients (bilirubin >300 umol/L) may show false-positive serum paracetamol results.Paracetamol toxicity or N-acetycysteine can negatively interfere with lactate, urate, total cholesterol, HDL-cholesterol and triglyceride assays. Exercise caution in interpreting these results.