Fludrocortisone suppression test for hyperaldosteronism
This test is considered by some to be the definitive diagnostic procedure for hyperaldosteronism.
The risk of sodium loading prohibits the use of this test in in elderly subjects and those with severe hypertension.
Patients with hyperaldosteronism are in a state of salt retention and excess sodium is lost in the urine. Therefore further sodium loading with a sodium retaining steroid will have no effect on plasma aldosterone. Adequate potassium needs to be administered to ensure that aldosterone secretion is not inhibited by hypokalaemia.
Hypokalaemia is common during this test.
- Fludrocortisone 0.1 mg tabs x 16
- Slow Na (10 mmol) tabs x 36
- Slow K (8 mmol) tabs - may need up to 200 tablets
- Li heparin blood tubes x 2
- Day 1: Plasma aldosterone should be measured mid morning. The subject should be upright for at least 30 min prior to venepuncture.
- Fludrocortisone 0.1 mg is administered 6 hourly for 4 days
- Slow Na 3x10 mmol tabs are administered 8 hourly for 4 days
- Plasma potassium should be measured at least twice daily and Slow K tabs administered in sufficient quantity to maintain plasma potassium normal
- Day 4: Plasma aldosterone should be measured mid morning. The subject should be upright for at least 30 min prior to venepuncture.
Serum aldosterone > 140 pmol/L at the end of the study confirms a diagnosis of Primary hyperaldosteronism.
Sensitivity and Specificity
Interpretation may be complicated by two factors if the patient remains recumbent which may result in false lowering of aldosterone. Firstly, aldosterone shows a similar though less marked diurnal rhythm to cortisol with a fall in concentration as the day progresses although this is overcome by the effect of angiotensin if the patient is ambulant. Secondly, some tumours are responsive to angiotensin, and aldosterone will consequently be lowered by prolonged (eg > 2 hours) recumbence.
Comparison of this fludrocortisone suppression test with an iv saline loading test in a series of 100 subjects suggests that the latter is equally efficient as a diagnostic tool whilst being easier, cheaper and potentially safer (Mulatero et al 2006).
- Gordon RD, Stowasser M, Klemm SA, Tunny TJ. Primary aldosteronism and other forms of mineralocorticoid hypertension. In: Swales JD (ed) Textbook of Hypertension. Blackwells Science, Oxford. 1994:865-892.
- Kem DC, Weinberger M, Gomez-Sanchez C, Kramer NJ, Lerman R, Furuyama S, Nugent CA. Circadian rhythm of plasma aldosterone concentration in patients with primary aldosteronism. J Clin Invest 1973;52:2272-2277
- Mulatero P, Milan A, Fallo F, Regolisti G, Pizzolo F, Fardella C, Mosso L, Marafetti L, Veglio F, Maccario M. Comparison of confirmatory tests for the diagnosis of primary aldosteronism. J Clin Endocrinol Metab 2006;91:2618-2623.
- Streeten DH, Tomycz N, Anderson GH. Reliability of screening methods for the diagnosis of primary hyperaldosteronism. Am J Med 1979;67:403-413.
JHB 8 Apr 2010