1. Results in 80 patients with primary aldosteronism (70 with tumour, 10 with hyperplasia) who underwent stimulation and suppression tests were analysed to assess the usefulness of several screening techniques.
2. On normal dietary sodium, normokalaemia was found in 27.5% of patients; 12.5% remained so despite 3 days of salt loading. Suppressed plasma renin activity (PRA: less than 1.43 pmol/l after stimulated conditions) gave a false-negative rate of 36%. Thus sole reliance on either hypokalaemia (serum potassium less than 3.5 mmol/l) or suppressed PRA as primary screening tests would have overlooked about a third of the patients in this series.
3. The single best diagnostic test for primary aldosteronism was the measurement of aldosterone excretion rate after 3 days of salt loading.
4. An anomalous postural fall in plasma aldosterone concentration when present, coupled with adrenal venous sampling, provided the best indicators of the presence of an aldosterone-producing adenoma.