Endocrine Abstracts

A 48-year-old woman presented to her GP with polyuria and proximal muscle weakness. She was found to have newly developed hypertension at 180/96 and her serum potassium was 2.7 mmol/l. Lisinopril 40 mg od and Slow-K 1 tablet bd were started and she was referred for further investigation.

On clinic review blood pressure was 188/110 supine and 190/110 standing. Serum sodium was 147 mmol/l, potassium 3.7 mmol/l and total bicarbonate 29 mmol/l. Her Lisinopril was replaced with Doxazosin and her Slow-K dose was increased to 2 tablets tds. Six weeks later, serum potassium was 4.0 mmol/l, urinary sodium excretion was 100 mmol/24 h and potassium excretion was 110 mmol/24 h. After overnight recumbency, plasma renin determined by immunoassay was 36.4 μ/l (supine 2–30), 35.7 μ/l (ambulant 3–40), aldosterone was 104 ng/l (10–160 ng/l) and 11-deoxycortisol was 71.3 nmol/l (<20.9 nmol/l). Serum cortisol suppressed to 34 nmol/l in a 1 mg overnight dexamethasone test. Urine catecholamine excretion was normal. Abdominal CT revealed a 6.6×7.8 cm left adrenal mass with appearances suggestive of an adrenal carcinoma. This was surgically excised by radical adrenalectomy together with her left kidney and spleen. In contrast to the result of renin immunoassay measurement made earlier, plasma renin activity measured preoperatively was <1.1 pmol/ml per h (2.8–4.5 pmol/ml per h).

Postoperatively her blood pressure normalised rapidly (125/72), her serum potassium rose to 5.0 mmol/l, and she maintained an eGFR of 54 ml/min consistent with unilateral nephrectomy. She remains normotensive and normokalaemic whilst taking adjuvant Mitotane prophylactically. There is an increasing trend for clinical laboratories to report plasma renin by immunoassay rather than by activity. In this case plasma renin level measured by immunoassay failed to suppress despite clear evidence of excess mineralocorticoid secretion by an adrenocortical carcinoma. The possibility that renin determinations by immunoassay may occasionally generate false negative results in patients being screened for Conn’s syndrome should be examined.