Paracetamol (Blood)

Diagnostic Use

Blood paracetamol levels assess overdose risk and guide antidote (NAC) treatment.

Reference Intervals

Toxicity of Paracetamol Poisoning

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 is 4 hours. Beware of incomplete absorption prior to 4 hours post ingestion. Specimens collected earlier than 4 hours may not indicate the peak serum concentration. The nomogram below can only be used in acute immediate release paracetamol ingestions with a known time of ingestion. In case of acute modified release paracetamol ingestion or repeated supratherapeutic ingestion, different management protocol/flow chart should apply – refer to your local centre for most up-to-date information.

                              New Paracetamol treatment nomogram for Australia and New Zealand

“From Daly FFS et al. Guidelines for the management of paracetamol poisoning in Australia and New Zealand – explanation and elaboration. A consensus statement from clinical toxicologists consulting to the Australasian poisons information centres. MJA 2008; 188 (5): 296-301. ©Copyright 2008. The Medical Journal of Australia – reproduced with permission” – same as the updated version from Chiew AL et al. MJA 2020 Mar; 212(4): 175-183 (see ref. 2 below) 

The serum paracetamol concentration (umol/L) on the y axis is read against the time (in hours) since paracetamol ingestion on the x axis.

Be aware : unit used for plasma paracetamol is umol/L (NOT mg/L)

Note :
– Treat ALL patients with serum paracetamol levels above the nomogram treatment line.

– Massive paracetamol overdoses that result in high paracetamol concentrations more than double the nomogram line may benefit from an increased dose of acetylcysteine. Consult local protocol/management flow chart.

References:
Graudins A et al. Early presentation following overdose of modified-release paracetamol (Panadol Osteo) with biphasic and prolonged paracetamol absorption NZMJ 2009; 122 (1300) : 64-71

Chiew AL et al. Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand. MJA 2020 Mar; 212(4): 175-183