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.
05 Sep 2020 - 09 Sep 2020