Predicting the outcome of the CaNa2EDTA challenge test in children with moderately elevated blood lead levels.

The Centers for Disease Control and Prevention suggests the challenge test for children whose blood lead levels are 1.21-2.12 micromol/L (25-44 microg/dL). However, the challenge test is difficult to perform. By identifying children who are likely to have a negative challenge test, a medical provider can minimize the number of children undergoing this test. The goal of this study was to identify common tests that are likely to predict the outcome of the challenge test. It was conducted as a clinical descriptive study from a series of patients who underwent a CaNa2EDTA challenge test. Results from 178 challenge tests were eligible for analysis. The mean age of children undergoing the challenge test was 38.2 months, and the mean blood lead level was 1.83 micromol/L (38 microg/dL). Blood lead level, age, erythrocyte protoporphyrin level, and RATE (a measure of the rate of change of the blood lead level) were either not sensitive or not specific in predicting the outcome of a challenge test. However, based on a logistic regression model using blood lead level, age, and RATE, we determined criteria that would have identified all children who would have had a positive challenge test while excluding most children who would have had a negative challenge test. Based on this model, we recommend that the challenge test be conducted on children >=36 months of age who have a blood lead level between 1.45 and 1.64 micromol/L (30-34 microg/dL) and on children who have a blood lead level 1.69-2.12 micromol/L (35-44 microg/dL) regardless of age. This approach would have tested all children who subsequently would have had a positive challenge test while testing only 39% of children who would have had a negative challenge test.