Analytical accuracy of determinations of aminoglycoside concentrations by enzyme multiplied immunoassay, fluorescence polarization immunoassay, and radioimmunoassay in the presence of heparin

The accuracy of gentamicin, netilmicin, and tobramycin concentration determinations by enzyme multiplied immunoassay technique (EMIT; Syva Corp., Palo Alto, Calif.), fluorescence polarization immunoassay (TDx; Abbott Diagnostics, Irving, Tex.), and radioimmunoassay were compared in the presence of 0 to 3,000 USP units of porcine heparin per ml. Gentamicin, netilmicin, and tobramycin concentrations determined by EMIT decreased by 10 and 50% in the presence of 75 and 1,000 USP units/ml, 2 and 5 USP units/ml, and 2 and 7.5 USP units/ml, respectively. Accuracy of the TDx and radioimmunoassay determinations, however, were not affected by the presence of heparin. Blood samples for the determinations of gentamicin, netilmicin, and tobramycin by EMIT should not be collected in evacuated heparinized tubes.