Preparation of prostate specific antigen standards for immunoradiometric assay

Prostate cancer is the sixth most common cancer in the world, the third most common cancer in men. In 2000, the number of new cases of prostate cancer was estimated at 513000 worldwide and this disease accounts for 9.7% of all cancers in men (1, 2). Thus early detection and local treatment have been advocated in an effort to influence the significant morbidity and mortality associated with the disease. Prostate specific antigen (PSA) is a glycoprotein of 30 KDa found mainly in prostatic tissue and specific for prostatic tissue normal or malignant. It has been identified to be present in normal, benign hyperplastic and malignant prostatic tissue, in metastatic prostate carcinoma, and also in prostatic fluid and seminal plasma. Pathologically increased production of PSA is a characteristic for malignant prostatic tissues. Considerably increased PSA levels in patients with bone metastases demonstrate their prostatic origin. The determination of PSA is based on the biochemistry and immunoassay methods, such as: radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) (5, 6). Today, one of the most common methods for analysis of PSA is immunoradiometric assay (IRMA) which is one of the RIA methods. In this method two monoclonal antibodies against two different epitopes of PSA molecule are used. An IRMA kit used in clinical laboratories is consisted of four main components including, Background: Immunoradiometric assay is one of the most common and precise methods for determination of prostate specific antigen (PSA) in clinical laboratories. Usual use of human serum in routine assays has many disadvantages; such as easy contamination and precipitation, instability and unavailability. Thus in order to avoid these problems the artificial matrix was used which acts similar to human serum. Materials and Methods: In order to design immunoradiometric assay for prostate specific antigen, series of standards in different concentrations were needed for special artificial matrix preparation. The influence of artificial matrix in standards was studied to determine prostate specific antigen in comparison with human serum. Some different factors, such as the amount of non-specific bonding (NSB), precision, and accuracy, conditions of storage and stability of these standards prepared by artificial matrix were investigated. Results: The most appropriate artificial matrix (Tris-glycine (25.0 mmol/L) + NaCl (75.0 mmol/L) + Tris (12.5 mmol/L) +Triton X100 (0.5 ml/L) + HSA (1.2 g/L) + Urea (0.5 mol/L)) for preparing the standards was selected in comparison with human serum (HSA) and a commercial kit standards. HSA and Urea concentration have more critical influences on the properties of the standards. The amount of NSB of the selected matrix was the lowest one, so the selected matrix was the most suitable for preparing the standards. The results show the optimum condition of storage duration of our standards for one year was in refrigerator (2-8°C). It was observed that preparation of standards with selected matrix had acceptable accuracy and precision. Conclusion: According to the results, standards which were prepared with this matrix had suitable and appropriate properties and it could be utilized to prepare PSA standards in immunoradiometric assay. Iran. J. Radiat. Res., 2008; 6 (1): 51-58