Use of NaCl 9‰ as a cheap diluent for cortisol assay in lateralized samples from adrenal veins catheterisation

Among the tools necessary for the diagnosis of primary hyperaldosteronism, catheterization of the adrenal veins represents the major examination to determine the presence of lateralized aldosterone secretion. To ensure that the catheter is well positioned at the level of the adrenal veins, a cortisol dosage is carried out in parallel with the aldosterone dosage. At the Hormonology and Tumor Markers laboratory of the Bordeaux University Hospital, this cortisol assay is carried out on an Abbott Architect i2000, making it possible to extend the calibration range up to > 3,300 nmol/L. Beyond that, the supplier recommends carrying out a manual dilution using calibrator A in which the cortisol concentration is equal to 0 nmol/L. The downside is that this calibrator cannot be supplied alone. It is only available in a common box with the 5 other calibrators necessary to carry out the cortisol calibration range. To overcome this expensive strategy, we studied the use of another diluent: 0.9% NaCl. Samples from 11 CVS were diluted with 0.9% NaCl and a comparison of cortisol results was performed (n = 128). Passing-Bablok regression of cortisol concentrations did not show significant deviation from linearity. The interpretation of CVS selectivity was not impacted by the change of diluent nor the interpretation of secretion lateralization. This change of diluent therefore did not modify the appropriate medical decision: medicinal treatment in the case of the identification of a bilateral secretion or proposal for surgical intervention in the case of the identification of a lateralized secretion.