Hematofluorometric determination of erythrocyte zinc protoporphyrin: oxygenation and derivatization of hemoglobin compared.

We compared oxygenation and derivatization of hemoglobin for the hematofluorometric determination of erythrocyte zinc protoporphyrin (ZPP). No statistically significant differences were found when the volume ratio of sample to ProtoFluor reagent (which converts hemoglobin to cyanohemoglobin) was changed from 1:1 to 1:4. With the derivatizing reagent, results were significantly higher than those obtained after thorough aeration of the blood sample (P < 0.001). The differences between the results obtained by the two procedures were greater for ZPP values in the reference range. Although the correlation between methods was high (r = 0.997), interconversion of the results by means of the regression equation was not acceptable because the standard error of the estimate from the regression (Syix = 0.36 micrograms/g hemoglobin) was greater than the error acceptable medically (criterion of Harris: Arch Pathol Lab Med 1988; 112:416-20).