Identi-PSA®

The prostate specific antigen (PSA) is an intracellular glycoprotein (molecular weight: 34,000 daltons) only synthesised by the male prostate gland and in seminal plasma.

This protein is now used by the forensic medicine as a choice marker to detect sexual assaults, even when they are committed by men who had vasectomy.

BLUESTAR® Identi-PSA® is a rapid qualitative assay for PSA detection from traditional biological samples (serum, plasma, or blood), but also from sperm samples collected with a swab either on the clothes or on the victims’ bodies.

The method employs a unique combination of monoclonal dye conjugate (mouse) and monoclonal antibodies (solid phase) to selectively identify PSA antigen in the samples, with a high degree of sensitivity.

As the test sample flows through the absorbent paper, the labelled antibody-dye conjugate binds to the antigen, thus forming an antigen-antibody complex. This complex binds to the anti-PSA antibodies in the positive reaction zone (T) and produces a wine-couloured line if the PSA antigen level is higher than 4 ng/ml. If there is no antigen, no line appears in the test zone.

The reaction mixture continues flowing through the absorbent paper, past the test zone and the control zone (C). Unbound conjugate binds to the reagents in the control zone, producing a wine-couloured band indicating that the reagents are functioning correctly.

An assessment of the BLUESTAR® Identi-PSA® test was performed in 1997 in order to use it in forensic medicine. The publication of these results shows that the BLUESTAR® Identi-PSA® test is perfectly suitable for this use as far as sensitivity, specificity, and feasibility are concerned. The test offers both very high sensitivity and high rapidity, as well as simplicity compared with a traditional ELISA method.

Intra-assay: Within run precision was determined by using 10 replicates of three specimens containing 0, 5 and 10 ng/ml of PSA. The negative and positive values were correctly identified 100% of time.

Inter-assay: Between run precision was determined by using the same three specimens of 0, 5 and 10 ng/ml of PSA in 10 independent assays and with three different lots of reaction device over a 6 months period. Again, the negative and positive values were correctly identified 100% of time.

The BLUESTAR® Identi-PSA® test can detect PSA levels higher than or equal to 4 ng/ml according to the international PSA standard (CRM 613 N°1004 from the European Standard Office, Belgium 1998). However, some samples containing less than 5 ng/ml may cause positive results.

Some samples containing very high PSA levels (up to 10 μg/ml) constantly caused positive results. However, some negative sperm samples caused positive results after 1/100 or 1/1,000 dilution. In case of doubt for some samples, it is then necessary to make another assay after 1/100 or 1/1,000 dilution.