Cortisol Measurement at Point of Care or Use: A Portable Fluorescence Immunoassay Method Using Capillary (Finger Prick) Samples

Abstract

In this chapter, we describe a quantitative fluorescence immunoassay (FIA) for the quantitative determination of cortisol in finger prick samples using a handheld device (ichroma™ M3). It gives a signal which is directly proportional to the cortisol concentration in plasma samples with a performance time between 10 and 15 min. The assay has a working range of 50–800 nmol/L. The precision of the assay (repeatability, within-laboratory, lot to lot, between person, between sites) is <7.1%. There is very little cross-reactivity (+/− 5%) with Cortisone, Corticosterone, Progesterone, Prednisone, Testosterone, Prednisolone, Deoxycortisol, DHEA, Dexamethasone. With minimal interference (+/− 5%) from D-glucose, L-Ascorbic acid, Bilirubin, Haemoglobin, Cholesterol and Triglyceride. There is very good agreement between the cortisol estimates of the bioMerieux Mini VIDAS (reference) and ichroma™ M3. In addition, cortisol estimations could also be performed on whole blood K2-EDTA, whole blood K3-EDTA and whole blood Li-Heparin samples. The ichroma™ cortisol method was able to detect the circadian rhythm in a healthy volunteer using finger prick samples and handheld device.