Evaluation of erythrocyte protoporphyrin and zinc protoporphyrin as micro screening procedures for lead poisoning detection.

Seven hundred and three blood samples from children were analysed for lead by Delves cup atomic absorption, for protoporphyrin by solvent extraction and fluorescence, and for zinc protoporphyrin with two manufacturers' models of automated front-face fluorimeter (haemato-fluorimeter). This power of protoporphyrin analysis for predicting the level of lead in blood was found to be poor. Up to 30% of children with lead concentrations of greater than or equal to 40 g/100 ml (greater than or equal to 1.93 mumol/l) and nearly 60% of children with greater than or equal to 30 microgram/100 ml (greater than or equal to 1.45 mumol/l) would remain undetected if protoporphyrin analysis were used for screening with an action level of 60 microgram/100 ml (1.07 mumol/l) for the porphyrin analysis. The predictive power of protoporphyrin analyses improves with the age of the child, indicating that the less expensive protoporphyrin test may be acceptable for older children, if by this means a large population of children at risk can be screened.