Specimen requirement | Spot urine: Plain urine bottle Volume: 10 mL |
Authorisation code required | Yes |
24 Hr available service | Yes |
Method | Colourimetric method |
Reference interval | Normal: negative |
Clinical indication | Screen for paraquat poisoning. |
Result interpretation |
Paraquat, used as a herbicide, is implicated in accidental and deliberate poisoning. A dose of 3 g is likely to be lethal and is contained in only 15 mL of the most potent preparations. After a single oral dose, acute ulcerative damage occurs in those parts of the skin and mucous membranes in contact with the poison. More serious effects on the liver, kidney and heart occur 2 or 3 days later. Later still, signs of pulmonary dysfunction appear with dyspnoea and pulmonary oedema leading to a progressive fatal pulmonary fibrosis. Ingestion of paraquat is still associated with a high mortality and the outcome is still more dependent on the amount ingested than on treatment. Paraquat is absorbed rapidly from the gut giving peak plasma concentrations within 1 Hr. Thereafter the concentration falls precipitately due to very rapid distribution into tissues and equally rapid clearance from the blood by renal elimination. Paraquat is retained in the tissues for much longer and its slow redistribution is responsible for the prolonged low plasma concentrations. Most seriously poisoned patients die from multiorgan failure and relatively few from pulmonary fibrosis alone. Since there is no specific therapy for paraquat poisoning, the assay is an approximate but useful prognostic indicator during the first 24 Hr after ingestion. |
Measurement of uncertainty | See table. |
Frequency of measurement | Urgent |