Recent evidence highlights a spectrum of renin-independent aldosteronism contributing to hypertension, with primary aldosteronism (PA) being the most well-characterised cause. PA has been associated with an increased risk of osteoporosis and fractures. Several studies have reported a correlation between serum parathyroid hormone (PTH) levels and PA; however, the relationship between PTH and PA within the broader spectrum of renin-independent aldosteronism remains unexplored. This study aims to elucidate the relationship between calcium, PTH, and aldosterone across the spectrum of renin-independent hypertension.
Adults with hypertension and a PTH measurement (n=483) were retrospectively identified from the Monash Health Endocrine Hypertension Clinic. All patients had undergone a diagnostic workup for PA including screening with an aldosterone-to-renin ratio (ARR) and confirmation with the saline suppression test. Patients were categorised into three groups: those with normal renin, low renin (<10 mU/L) but not meeting the criteria for PA, and PA.
PTH levels were significantly higher in patients with PA compared to those without PA (median 5.7 vs 5.2 pmol/L, p<.001), and in unilateral compared to bilateral PA (7.0 vs 5.8 pmol/L, p=.014), despite comparable vitamin D and serum calcium concentrations. PTH levels increased progressively across the spectrum of renin suppression (5.0pmol/L in patients with normal renin, 5.3pmol/L in low renin and 5.7pmol/L in PA, p=.016). 24-hour urinary calcium excretion was significantly higher with greater renin suppression (4.1 vs 4.3 vs 4.9 mmol/day in the respective groups of low renin, normal renin and PA, p=.040). Patients with PA were more likely to have normocalcemic hyperparathyroidism compared to those without PA (37% vs 23%, p=.002). PTH concentration correlated with a diagnosis of PA after adjusting for age, sex, vitamin D and eGFR (p=.002).
Elevated PTH and 24-hour urinary calcium excretion was observed in renin-independent aldosteronism. PA should be considered as a differential diagnosis in patients with normocalcemic hyperparathyroidism.