New enzyme immunoassay for salivary cortisol.

concentration of a sample that gave an absorbance value within the linear range of the assay and was expressed relative to the absorbance/␮g of BSA (corresponding to the gradient of the calibration curve): Interference ϭ absorbance/␮g of aminoglycoside absorbance/␮g of BSA ϫ 100% The aminoglycosides gave negligible interference in the CBB assay (Ͻ0.2% relative to BSA) and failed to generate turbidity in the BEC assay. Aminoglycoside interference in urine was demonstrated with urine control containing the aminoglyco-sides at 0.2 g/L. Although the data are based on model experiments, they reflect aminoglycoside concentrations that could reasonably be present in urine from patients (1). The PRM control value (0.36 Ϯ 0.01 g/L protein) increased 244% with neomycin (1.24 Ϯ 0.01 g/L), 142% with gentamicin (0.87 Ϯ 0.02 g/L), 111% with tobramycin (0.76 Ϯ 0.02 g/L), 53% with paromomycin (0.55 Ϯ 0.02 g/L), 11% with genet-icin (0.40 Ϯ 0.01 g/L), 8% with kanamycin (0.39 Ϯ 0.01 g/L), 3% with streptomycin (0.37 Ϯ 0.01 g/L), and 3% with dihydrostrep-tomycin (0.37 Ϯ 0.02 g/L; n ϭ 5; CV Ͻ5.5%). The interference was significant (P Ͻ0.01) with neomycin, gentamicin, tobramycin, paromomy-cin, geneticin, and kanamycin but not significant (P Ͼ0.1) with strepto-mycin or dihydrostreptomycin. In contrast, neither the CBB control value (0.21 Ϯ 0.01 g/L protein) nor the BEC control value (0.28 Ϯ 0.01 g/L) were affected by aminoglyco-sides at 0.2 g/L. Thus, in contrast to the Roche and Cobas Fara PRM assays, which are resistant to aminoglycoside interference , the Sigma PRM assay resembles the Dade Behring PRM assay in its susceptibility to interference (1). This may reflect the formulation of the reagents or the volume ratio of sample to reagent. The clinical importance of this interference is evident for tobramycin [at urinary concentrations Ͼ0.2 g/L (1)] but more difficult to assess for the other ami-noglycosides, whose urinary concentrations do not appear to have been reported. In conclusion, we have confirmed interference in the PRM assay by gentamicin, neomycin, and tobra-mycin (1–3); reported interference from additional aminoglycosides; and demonstrated a susceptibility of the Sigma PRM assay to interference from aminoglycosides in urine at 0.2 g/L. In contrast to the PRM assay, the CBB and BEC assays are resistant to aminoglycoside interference. Aminoglycoside interference with the Dade Behring pyrogallol red-molybdate method for the measurement of total urine protein [Letter]. as measured with a pyrogallol-red-molybdate complex manually and in a Hitachi 726 automated analyzer. Total protein determination in …