Endocrine Abstracts

The loss of nychthemeral rhythm is a feature of endogenous hypercorticism that may be investigated by the assay of midnight salivary cortisol (_serC0h) although often replaced by serum cortisol assay. However, manufacturers of cortisol immunoassays kits seldom provide reference values for this horary. We present here tentative reference values of _serC0h with an automated imunoanalyzer (DXi800, Beckman Coulter).

The population retrospectively studied (2014–2017) consisted of in-patients mainly investigated for diabetes, hypertension, and obesity (214F/121M, 57 [25–75] years, BMI 27.5 [20.2–41.2], median [5th–95th] percentile). The patients that elicited the strongest clinical suspicion of hypercorticism were subjected to urinary sampling for cortisol assay and/or low dose dexamethasone supressing test.

_serC0h (n = 415) was 93 [36–251] nmol/l with a non-gaussian distribution in subjects with no confirmed hypercorticism. The upper reference limit (URL) of _serF0 was 284 nmol/l (CLSI C28-A3 non-parametric method). Urinary free cortisol (UFC) was 17 [5–55] µg/d (ref 10–60 µg/d) Serum cortisol at 8 h (_serC8h) was 336 [189–623] nmol/l (DXi800 reference values 185–624 nmol/l). There was no significant correlation of _serC0h with BMI or UFC or _serC8h.

The 10 subjects exhibiting _serC0h>URL were diagnosed: metastatic cancer (3), pheochromocytoma (1), acromegaly (1), diabetes/alcoholism (1), stress (1), pseudoCushing syndrome (1) and adrenal incidentaloma (2). The stressed patient had normal UFC and low-dose DXM test (LDDT) 6 months later, the patient with pseudoCushing syndrome has the same status 3 years later. One patient with incidentaloma had normal UFC and LDDT 1 year later, and was later diagnosed multiple sclerosis. The other patient with incidentaloma had normal LDDT; adrenalectomy was requested because the tumour (30 mm) was heterogeneous with calcification but the patient was lost on follow-up.

We propose to use 284 nmol/l as URL for _serC0h using the DXi800 cortisol assay. Prospective studies are pending to provide clinical specificities and sensitivities at this level. Comparisons with other immunoassays are also needed.