Validation of a 10-minute dipstick test for serum prostate-specific antigen.

OBJECTIVE

The aim of this study was to determine the clinical usefulness of a recently developed one-step dipstick test for rapid (10 min) and semiquantitative analysis of serum prostate-specific antigen (PSA). The cutoff value of this semiquantitative dipstick test is 4.0 ng/ml.

METHODS

PSA levels of 238 serum samples were simultaneously determined by this dipstick test and by a 'classic' monoclonal antibody based PSA enzyme immunoassay. Interassay variations of the dipstick test were determined by repetitive analyses (n = 10) of three serum pools containing 1, 6, and 15 ng PSA/ml. Recovery studies with graded amounts of PSA were performed in normal sera (n = 5) as well as in those with elevated creatinine (n = 5) and bilirubin (n = 5) levels.

RESULTS

A total of 139 serum samples had PSA levels, determined by the enzyme immunoassay, < 4.0 ng/ml; 132 (94.9%) of which were negative with the dipstick test, and 7 (5.1%) were false-positive. Samples with a PSA value < 2.0 ng/ml (n = 102) were correctly recognized in 98.1% of the cases by the dipstick test. Serum samples with a PSA value of 4-10 ng/ml were false-negative in 10 of 41 cases (24.4%), the remaining (75.6%) were true positives. Samples containing PSA levels > or = 10 ng/ml (n = 58) were consistently positive. Hence, the overall concordance rate was 92.9%. Analyses of interassay variation of three pools of sera containing 1, 6, and 15 ng PSA/ml revealed a high reproducibility of this test. Elevated levels of bilirubin and creatinine did not interfere with the dipstick test result.

CONCLUSIONS

This semiquantitative one-step PSA test is capable of distinguishing serum PSA levels with a cutoff value of 4.0 ng/ml with an overall concordance rate of 92.9%. Advantages of this test are the cheap, simple, and fast test procedure, the avoidance of any instrumentation, and the fact that the results are available within 10 min.