National Registry in Clinical Chemistry

A recent Letter by Eckfeldt et al. (1) recalled some of our unpublished findings of a few years ago, showing the effect of sodium azide on continuous-flow (SMA 12/60) measurements (Table 1). The azide interference with total bilirubin determinations they reported can be also be seen in our results, although not conspicuously. As can be seen in Table 1, measurements other than bili-. rubin may be affected, and quite possibly, creatine kinase and alkaline phosphatase are depressed and apparent calcium is elevated with increased aside concentrations. Tests that were unaffected include lactate dehydrogenase, aspartate aminotransferase, creatinine, uric acid, phosphorus, albumin, protein, and cholesterol. The analysis of lyophilized sera (Versatol) reconstituted with identical concentrations of sodium azide gave similar, confirming results.