Erythrocyte protoporphyrin concentrations in clinically normal cats and cats with lead toxicity

Erythrocyte protoporphyrin (EPP) and blood lead concentrations were determined in 91 clinically healthy cats living in the inner suburban area of Sydney, Australia. The mean EPP concentration was 223.4 +/- 186.1 micrograms litre-1 whole blood and the mean blood lead concentration 0.62 +/- 0.25 mumol litre-1. EPP concentrations were also monitored in three cats with confirmed lead toxicity--at the time of diagnosis and one week and one month after chelation therapy with calcium EDTA. EPP concentrations were elevated in two cats and within the normal range in the third cat at the time of diagnosis. EPP concentration were higher in two cats one week after treatment than at the time of diagnosis. One month after chelation therapy, EPP concentrations were normal in two cats but still substantially elevated in the third cat although its blood lead concentration had returned to normal and all clinical signs of lead toxicity had resolved. It was determined that the predominant form of protoporphyrin present in cats with lead toxicity was zinc protoporphyrin. The EPP assay may have limited value in the diagnosis of acute lead toxicity and in monitoring the success of chelation therapy in cats.