Current challenges in laboratory diagnostics of autonomous cortisol secretion in adrenal incidentalomas

Adrenal incidentalomas are unexpectedly identified adrenal masses without prior suspicion of the existence of adrenal disease. The majority of adrenal incidentalomas are benign adrenal adenomas (80-90%), and they are non-functioning adrenocortical adenomas in more than 70% of cases. Mild hypercortisolemia is the most common finding in hormonally active adrenal incidentalomas. It is defined as autonomous cortisol secretion in up to 15% of patients. Despite a lot of research that anticipated higher cardiometabolic risk in patients with autonomous cortisol secretion, there is still no clear consensus on biochemical criteria for an autonomous cortisol secretion diagnosis in patients with adrenal incidentalomas. This review delineates the advantages and limitations of different laboratory tests recommended for the diagnosis of autonomous cortisol secretion in adrenal incidentalomas.

Variability in laboratory parameters used for management of Cushing's syndrome

The progress in assay methodology, from the use of radioactive tracers to chemiluminescent signals, from competitive to chromatographic techniques and from serum or urine to saliva has considerably impacted on hormonal measurements. The clinician now may choose among multiple tests but the inherent variability in cortisol and ACTH secretion, coupled to lack of harmonization among assay procedures and normal ranges mandates careful interpretation of any result. The present review will examine factors which affect interpretation of cortisol and ACTH measurements and their impact on tests used for management of Cushing's syndrome.

Multicenter evaluation of a rapid electrochemiluminescent adrenocorticotropic hormone (ACTH) immunoassay

BACKGROUND

Measuring plasma adrenocorticotropic hormone (ACTH) is a key step in the differential diagnosis of hypothalamic-pituitary-adrenal disorders.

METHODS

The recently developed electrochemiluminescence Elecsys ACTH immunoassay (Roche Diagnostics, Mannheim, Germany) was evaluated at six clinical laboratories on the Modular E170 and/or the Elecsys 2010 (Roche Diagnostics) immunoanalysers.

RESULTS

The within-run and between-run imprecision was <or=1.9% and <or=5%, respectively (concentration level 12-971 ng/L). Functional sensitivity was at least 1.8 ng/L. The Elecsys assay correlated well with two established ACTH immunoradiometric assays (Brahms ACTH RIA and Nichols ACTH IRMA) and with the Immulite ACTH assay. Reference values for the Elecsys ACTH assay, determined as the percentile 5 to 95 (2.5 to 97.5) interval in 354 adults without disorder with impact on the hypothalamic-pituitary-adrenal axis, were between 7.2 and 63 ng/L (5.6 and 76 ng/L). The clinical sensitivity of the Elecsys ACTH assay in 57 patients with confirmed disorders of the pituitary-adrenal axis was comparable to the established Brahms ACTH assay.

CONCLUSION

The non-isotopic Elecsys ACTH immunoassay provides precision and reliability in combination with reduced turnaround time.

Immunoradiometric assay of succinylated corticotropin: an improved method for quantification of ACTH

In this paper we describe the development and the evaluation of a new type of immunoassay for human corticotropin (ACTH). We succeeded, by using an original approach based upon immunization with ACTH derivatized with succinic anhydride, in raising monoclonal antibodies against this poorly immunogenic peptide. Three of the antibodies were selected to develop an immunoassay for ACTH. The assay requires the prior succinylation of the plasma samples for optimal sensitivity and specificity. This acylation treatment is fast, reproducible, and, in addition, improves the stability of the ACTH molecule in plasma, thus facilitating sample handling. The assay is performed in only 3 h with a detection limit of 0.7 ng/L. Analytical evaluation showed excellent specificity, reproducibility, and reliability. A comparison with two commonly used but time-consuming ACTH IRMAs was carried out by assaying several plasma samples in parallel and gave in both cases very good correlation.