The influence of plasma bilirubin on zinc protoporphyrin measurement by a hematofluorimeter.

A fluorimeter has recently been developed to detect lead poisoning and iron deficiency by measuring erythrocyte ZPP directly from whole blood. Plasma bilirubin fluorescence has been found to influence this technique. ZPP levels determined by the fluorimeter were elevated by artificially increasing the plasma bilirubin concentration, both within and above the normal range, in whole blood samples. A rise in ZPP levels were also observed when the hemoglobin concentration was lowered by dilution with native plasma. When blood samples of patients with hyperbilirubinemia were analyzed, direct measurement of ZPP by this fluorimeter yielded significantly higher levels than did an alternate extraction method. Photodegradation of bilirubin in whole blood samples did not decrease fluorescent interference. Although the bilirubin measurably decreased, fluorescence increased following a 5 hr exposure to light.