A positive CaNa2 EDTA provocative chelation test (PCT) is the gold standard for deciding on which patients (PTS) with a blood lead level (BLL) of<45.0 ug/dl should receive chelation therapy. This test, however, can cause major discomfort and/or injury, hence the desire to diminish PCT use is warranted. With this objective, we reviewed BLL, ferritin, serum iron and free erythrocyte protoporphyrin (FEP) levels in 29 PTS at the time of standard PCT to examine other variables as surrogates of positive PCT as effective indicators of chelation suitability. The combination of FEP and BLL demonstrated the most statistically significant discriminatory factors. FEP correlated significantly with a positive PCT ratio = 0.6 (r = 0.483, p = 0.08). Using an FEP level of >45.0 ug/dl as a threshold for undertaking PCT, we eliminated 11 PTS of the original 29 prospectively requiring PCT in the study. All 11 PTS demonstrated a negative PCT thus providing no false positive PTS. Adding an additional screening step for the remaining 18 PTS, that being a BLL of >30 ug/dl for indication to perform PCT, we reduced that candidate group by 6 PTS with only a single positive PCT (false negative). By using a two-step approach for PCT qualification, the effect in our study is to eliminate 17 of the 29 PTS (59%) needing PCT with a false positive rate of 34.5% and a false negative ate of 3% (one PT). In summary, our two-step approach elimination procedure is useful in diminishing the need for PCT in deciding which children with moderate lead toxicity require chelation.
