4 Early assessment of the risk of liver damage requires urgent measurement of the patient's plasma paracetamol concentration. Blood should be taken for this purpose as soon as 4 hours or more have elapsed since the overdose. Plasma concentrations taken within 4 hours should not be requested as they cannot reliably be interpreted because of the possibility of continuing absorption and distribution of the drug. The time interval since ingestion is critical in assessing whether treatment is required but is often difficult to establish. Detailed questioning of the patient and others is necessary.
Patients often give inaccurate histories.
If there is doubt about the timing or the need for treatment, treat. The treatment lines on the accompanying graph are estimates of risk based on the best available clinical evidence. They are critically dependent upon the accuracy of the history with respect to time of overdose ingestion. Beyond 15 hours, the risk estimates are even less reliable and clinical judgement becomes more important in management. 7 Staggered overdose .