Serum gentamicin assays of 100 clinical serum samples by a rapid 40 degrees C. Klebsiella method compared with overnight plate diffusion and acetyltransferase assays.

We have compared the results of gentamicin assay of 100 clinical serum samples by a rapid 40 degrees C plate diffusion method, an overnight plate assay at 37 degrees C, and radioactive acetyltransferase methods. The results of assay obtained by both plate diffusion methods agreed closely. There was excellent correlation between the results of acetyltransferase and plate assays provided that human serum gentamicin standards were used for the acetyltransferase assay and turbid sera were excluded. Lipaemic sera were associated with falsely high results by the acetyltransferase method. There was no difference in specificity between the methods when antibiotics other than gentamicin were present. Much less skilled technician time was required to perform the rapid 40 degrees C plate method than the radioactive acetyltransferase method. The 40 degrees C plate method is preferred for routine serum gentamicin assays in our clinical laboratories.