RESUMEN
OBJECTIVE: CMA is a widespread glycoprotein located in the secretory vesicles of neuroendocrine cells and is co-released with peptides and biogenic amines into the circulation. The present study set out to investigate the clinical utility of assessing serum CGA levels in comparison with the urinary KTCO and their urinary metabolites concentrations, which are to date the gold standard validated diagnostic test. METHODS: From January 2000 to June 2001, 202 consecutive patients, aged 53 +/- 12.7, 102 males, were admitted to our department for a hypertension evaluation. Blood samples for measurements of plasma concentrations of chromogranin A were collected and serum CGA levels were quantified by RIA technique (RIACT). This radioimmunometric technique consisted in using 2 monoclonal antibodies directed to 2 specific antigenic domains of the middle portion of the CGA. The fixed threshold value for identifying positive results was, set at 100 ng/ml according to previous studies. RESULTS: No pheochomocytoma was diagnosed by conventional urinary KTCO essay. Of the 202 CGA blood samples, 32 turned out to be positive, due to commonly encountered false positive causes (inhibitor of the pump with protons, corticotherapy, hypergastrinemia, chronic renal insufficiency, respectively, in 11, 2, 1, 18 cases). The CGA plasma concentration averaged 77 +/- 77 mg/ml and 203 +/- 125 ng/ml in the CGA subgroup over the threshold value. CONCLUSION: The reliability of immunoradiometric serum CGA concentrations appeared according to this work to be comparable to that of the urinary KTCO levels and their urinary metabolites in hypertensives. Moreover, it solely requires a simple, easily done blood taking, less expensive than urinary KTCO collection. Besides, no antihypertensive drugs interfered with the analysis of CGA levels. However, some false positive results have to be mentioned in the presence of renal impairment, hypergastrinemia, corticotherapy, inhibitor of the pump with protons.