The measurement of erythrocyte zinc protoporphyrin (ZPP), a product of abnormal heme synthesis, is a simple and precise measure of IDE but stil not widely used for clinical purposes. One important advantage is the ability to measure the ratio of ZPP/heme directly on a drop of whole blood using a dedicated portable instrument called a hematofluorimeter. The ZPP is ideally suited for field surveys of iron status or pediatric and obstetrical clinics where uncomplicated iron deficiency is relatively common. The ZPP is redundant in laboratories equipped for percentage hypochromic red cell measurements because the two tests provide similar information. ZPP increases with lead toxicity and falsely elevated values and can occur in patients with elevated serum bilirubin or on regular hemodialysis, although the interference can be eliminated with prior washing of the red cells.