How alternative are immunoassay systems employing non-radioisotopic labels? A comparative appraisal of their main analytical characteristics.

The immunoassay is one of the most sensitive and reliable analytical techniques available in the clinical laboratory. The original label for immunoassays was radioisotopes, and these methods, radioimmunoassay (RIA) and immunoradiometric assay (IRMA) are still the reference methods, because of invulnerability of the radioactive emission with respect to environmental interference. Labels other than radioisotopes have been tested for use in immunoassay to improve the sensitivity and reliability and to avoid some of the disadvantages of radioisotopic techniques. New labels have continued to be developed (Horseradish peroxidase-HPR-, pyrophosphatase, luciferases, pyrodopirazines, europium cryptates, porphirins, phosphors) and new label detection methods have been set up (e.g. chemiluminescence assay, thermometric assay, NADP+ and FADP- based coupled assay). New immunoassay strategies such as simultaneous multianalyte automated test have been developed and the reliability of the assays has in some cases caused division among researchers about the choice between the radioisotopic immunoassay or the non-radioisotopic immunoassay, as considerable effort and investment had been devoted to the search for more sensitive and practicable tests than the classic RIA-IRMA methods. The evolution of immunoassays (Monoclonal Antibodies, non-radioactive tracers, automation) has produced systems which allow a large number of laboratories to determine a great number of analytes with very good practicability. The availability of fully automated systems has generated the opinion that analytical performance of immunoassays can be considered similar to that of many traditional parameters of clinical chemistry. This conclusion seems however too optimistic, in fact data collected from interlaboratory studies demonstrate that problems concerning the analytical reliability of the measurements still remain not completely solved. In the authors' opinion, this opposition between immunological assay based on isotopic or non-isotopic labels is misleading, because each assay (whether it uses isotopic, enzymatic, fluorimetric or luminescent labels) has its own analytical characteristics and performance. For this reason the term "alternative", used to indicate all non-isotopic assays as a unique class of tests, should be abandoned. From a theoretical point of view the choice should not be between isotopic and non isotopic techniques. For each analyte to be tested, it is advisable to use the immunological assay that suits the requirements of the laboratory, irrespective of type of label. From a practical point of view, the choice should be based on the analytical performance and on the characteristics of each assay, on its cost and the type of instrumentation available in the laboratory, and on the experience and the knowledge of the laboratory personnel.

Prospective multicenter study on CA 125 in postmenopausal pelvic masses.

The purpose of this study was to determine the diagnostic value of CA 125 in comparison with transabdominal ultrasound (US) in the evaluation of postmenopausal women with pelvic mass to detect malignant epithelial ovarian tumors. Postmenopausal patients with pelvic mass were studied with gynecologic examination, US and CA 125 determination. Three hundred eighty-eight patients were entered in the study. According to stratification based on US (probably benign, equivocal, possibly malignant) and CA 125 (< 35 U/ml, negative; between 35 and 65 U/ml, borderline; > 65 U/ml, positive), 290 patients were considered eligible for surgery. Specificity, sensitivity, positive and negative predictive value, and accuracy of US and CA 125 were calculated with respect to histological examination. Out of 290 operated patients, 134 had a benign ovarian pathology, 34 had extraovarian benign pathology, 106 had an ovarian malignancy, and 16 presented with an extraovarian malignant pathology. The results according to ovarian malignant pathology were as follows. CA 125 (> 65 U/ml): Specificity, 92.5%; sensitivity, 71.7%; accuracy, 83.3%. CA 125 (> 35 U/ml): Specificity, 82.0%; sensitivity, 78.3%; accuracy, 80.4%. US: Specificity, 77.6%; sensitivity, 84.9%; accuracy, 80.3%. Combination of US and CA 125 (> 65 U/ml): Specificity, 96.1%; sensitivity, 91.7%; accuracy, 94.3%. Determination of CA 125 is a highly specific method in predicting ovarian cancer in postmenopausal women with a pelvic mass. The association with US significantly improves the overall accuracy and may support therapeutical decision making by distinguishing between a significant percentage of women most likely to benefit from prompt intervention and women who may be managed following minor surgical diagnostic approach, such as fine-needle aspiration.

Beta-endorphin concentration in the femoral and spermatic venous blood of males affected by varicocele.

Several studies in the rat indicate that opioid peptides produced in the testicular interstitial compartment can affect events in the tubular compartment. For example, it is thought that some specific functions of Sertoli cells, such as androgen-binding protein production are decreased by a paracrine mechanism. In this study ACTH beta-endorphin and cortisol were measured in the femoral and spermatic venous blood drawn from 18 patients affected by varicocele during catheterization for venous occlusion. The results showed the absence of a significant secretory gradient of beta-endorphin in the human testis and also demonstrated that this opioid is circulating at picomolar concentrations within human testis under stress conditions.