Since the metyrapone test gives similar information about hypothalamic-pituitary axis function as does the hypoglycaemia test, we recommend the use of the overnight metyrapone test as a safe, simple and reliable index of the hypothalamic-pituitary axis integrity. The ACTH stimulation test should not be used for patients suspected of having secondary adrenal insufficiency.

Theoretically, the relationship between plasma aldosterone (PA) and PRA in normal subjects under random conditions should differ from that in patients with primary hyperaldosteronism or primary adrenal failure, but should be similar to that in patients with secondary hyperaldosteronism or hyporeninemic hypoaldosteronism. PA, expressed as a function of PRA, the PA/PRA ratio, provides an index of adrenal sensitivity in normal subjects under routine conditions. The random PA/PRA ratios in patients with primary adrenal disorders did not overlap with those in normal subjects, patients with secondary adrenal disorders, hypertensive subjects, or other patients. A single elevated PA/PRA ratio, i.e. more than 920, associated with elevated PA in 4 patients or normal PA in 6 patients indicated primary hyperaldosteronism in 10 patients. However, 5 of 17 patients with chronic renal failure had elevated PA/PRA ratios, but did not have primary hyperaldosteronism. All 14 patients with secondary hyperaldosteronism had elevated PA associated with normal PA/PRA ratios. A single PA/PRA ratio of less than 28 associated with low PA in 18 patients and a normal PA in 1 patient indicated primary adrenal insufficiency, while a low PA associated with a normal PA/PRA ratio indicated hyporeninemic hypoaldosteronism in 7 patients. Fifty-nine patients with nonadrenal disorders other than renal failure had normal PA and PA/PRA ratios. Therefore, with the exception of patients with advanced renal failure, only a single blood sample is required to establish all diagnoses of disorders of the renin-angiotensin-aldosterone axis under random conditions.

Background: High C-reactive protein (CRP) and homocysteine levels are risk factors for cardiovascular disease. Some, but not all, previous studies have reported increased levels of CRP and homocysteine in patients with obstructive sleep apnoea syndrome (OSAS). A study was undertaken to investigate the levels of these factors in carefully selected patients with OSAS and matched normal controls. Methods: CRP and homocysteine levels were measured in 110 subjects following polysomnography (PSG). Non-OSAS patients (group 1) were compared with two patient groups (mild/moderate OSAS (group 2) and severe OSAS (group 3)) group-matched for body mass index (BMI), and a fourth group of patients with severe OSAS who were more obese (group 4). All were free of other disease and similar in age, smoking habits and cholesterol levels. 50 suitable patients were commenced on continuous positive airway pressure (CPAP) treatment after PSG and 49 were reassessed 6 weeks later. Results: CRP levels were similar in groups 1, 2 and 3 (median (interquartile range (IQR)) 1.11 (0.76-2.11) mg/l vs 1.82 (1.20-3.71) mg/l vs 2.20 (1.16-3.59) mg/l; p = 0.727, Kruskal-Wallis test), but were significantly higher in group 4 than in the other groups (5.36 (2.42-9.17) mg/l, p,0.05 by individual group comparisons). In multivariate analysis of all subjects, BMI was an independent predictor for CRP levels (b = 0.221; p = 0.006) but apnoea-hypopnoea index and other measures of OSAS were not. There was no difference in homocysteine levels between all four groups (p = 0.1). CPAP did not alter CRP (2.29 (1.32-4.10) vs 2.84 (1.13-5.40) mg/l; p = 0.145) or homocysteine levels (8.49 (3.66) vs 9.90 (4.72) mmol/l; p = 0.381). Conclusion: CRP and homocysteine levels are not associated with OSAS severity in men but CRP is independently associated with obesity.

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