Lead Zpp

Zinc protoporphyrin is ordered primarily to help detect iron deficiency in children and to detect and monitor chronic exposure to lead in adults. Lead inhibits the action of ferrochelatase, resulting in increased ZPP formation even when adequate amounts of iron are present. ZPP is thought to be a better screening test for lead burden (the total amount of lead being held by the body) than a lead concentration because lead levels tend to vary day to day in the blood and because lead moves from the blood into organs and bone. While blood samples for lead may be contaminated by any environmental lead present at the time of collection, ZPP is not affected.
In the general adult population, ZPP may be ordered, along with a lead level, as part of a screen for chronic lead exposure. Hobbyists that work with products containing lead and people who live in older houses are examples of people who may be at an increased risk of developing lead poisoning. This is because lead is usually ingested or inhaled. Those who inhale dust that contains lead, handle lead directly and then eat, or - in the case of children - eat paint chips that contains lead (common in houses built prior to 1960) can have elevated levels of lead and ZPP in their body. In an industrial setting, the Occupational Safety & Health Administration mandates the use of ZPP and strongly recommends that a ZPP test be ordered every time that a lead level is ordered to monitor an employee’s exposure to lead. Both are necessary because ZPP will not reflect recent or acute lead exposure, and it does not change quickly when a patient is removed from lead exposure. ZPP is best at detecting a person’s average exposure to lead over the last 3-4 months.

The maximum lead concentrations considered safe in children have been set at a very low level to minimize the negative impact of lead exposure on their development. ZPP is not sensitive enough for use as a screening test in children, as values do not rise until lead concentrations exceed the acceptable range. In this age group, blood lead measurements should be done to detect exposure to lead.

In children, the ZPP/heme ratio is frequently ordered as an early indicator of iron deficiency. It is one of the first signs of insufficient iron and will be elevated in most young people before signs or symptoms of anemia are present. Those with an elevated ZPP/heme ratio may require further testing to determine the cause. In some cases, a patient may have both lead exposure and iron deficiency.

ZPP also is occasionally ordered to help diagnose porphyrias. These are a group of rare inherited disorders that are caused by deficiencies in the enzymes necessary to produce heme. Deficiency of an enzyme leads to a bottleneck and the buildup of intermediate products that would normally be converted to heme. There are two porphyrias in which very high concentrations of ZPP and other porphyrins accumulate in red blood cells. The main symptom exhibited by these patients is extreme sensitivity to sunlight.