PSA quick test in capillary blood

The use of PSA quick testing methods with capillary blood (test strips) to screen for carcinoma of the prostate has been a controversial method.

The results determined visually from whole capillary blood were compared with the PSA values obtained from serum through quantitative assay and their correspondence was evaluated. PSA values <4 ng/ml obtained through quantitative assay were regarded and as negative results and PSA > or = 4 ng/ml as positive results.

Of 371 usable assays, 100 quantitatively obtained PSA values were positive and 271 negative. Seven test strips showed false-negative and 49 false-positive results. In comparison with the quantitative assay, this is equivalent to a sensitivity of 93% and a specificity of 82%. Comparing the distinction between PSA >4 and <4 ng/ml only, there was no significant difference between the results of the quick test and the quantitative assay (Fischer exact test, p < 0.000). Considering the PSA values between 4 and 10 ng/ml, 10.3% of the results of both methods differed.

Our series of experiments ascertained a relatively high rate of false-positive PSA test strip results. In practice this can lead to an unpredictable increase of costs, as every positive result requires a quantitative assay. Even more alarming is the loss of sensitivity in the PSA "between 4 and 10 ng/ml" range, which gives false-negative results leading to a delay of diagnosis and therapy.