La fase preanalitica nella misura del [-2]proPSA e dell'indice di salute prostatica

Prostate carcinoma is the most common cancer in men. The [-2]proPSA and derived Prostate Health Index (PHI) are new proposed markers for this neoplastic condition. Unfortunately, if the serum is not immediately separated from the clot, concentrations of [-2]proPSA spuriously increase in vitro. Aim of our work was to test if use of serum separator tubes or sample refrigeration were effective in stabilizing [-2]proPSA. Sera were collected from two groups of 25 and 35 patients requiring PHI estimate. From both groups, besides the usual serum sample, centrifuged and separated from the clot within a maximum of 90 min, additional samples in a tube with serum separator or in a second tube kept in a water-ice bath were taken. In both cases, the centrifuged sera were kept on the clot for 5 h at room temperature or in refrigerator and then separated and frozen at -80°C. All the aliquots were thawed and analyzed in the same run to avoid run to run variation. Both solutions, i.e. the use of serum separator or the immediate refrigeration of the sample, were effective in reducing the in vitro increase of [-2]proPSA. Unfortunately, the use of serum separator introduced a 5% negative bias in the measurement of total and free PSA, both necessary for the calculation of PHI, thus precluding the use of this type of sample. The immediate refrigeration stabilized the [-2]proPSA concentrations, but was unable to avoid free PSA reduction, so that the calculation of PHI was still inaccurate. In conclusion, [-2]proPSA can be effectively stabilized, but free PSA can not. Thus, for an accurate estimate of PHI, an immediate separation of serum from the clot is highly recommended.