Confirmatory testing in normokalaemic primary aldosteronism: the value of the saline infusion test and urinary aldosterone metabolites.
OBJECTIVE
Primary aldosteronism has recently been recognized as the most frequent cause of secondary hypertension. Since most patients are normokalaemic, differentiation to essential hypertension is challenging. As differentiation by baseline aldosterone/renin ratio may be insufficient, diagnosis should be confirmed by additional tests. However, as most confirmatory tests have been evaluated in hypokalaemic primary aldosteronism only, we reassessed the value of the saline infusion test and 24 h urinary aldosterone metabolites as confirmatory tests for both normo- and hypokalaemic primary aldosteronism under current antihypertensive medication.


METHODS
25 patients with primary aldosteronism (11 hypokalaemic, 14 normokalaemic), 29 patients with essential hypertension and 47 normotensive subjects were studied. The hypertensives received their usual medication with the exception of spironolactone. All subjects underwent a standard saline infusion test (determination of plasma aldosterone before and after 2.0 liters of isotonic saline for 4 hours i.v.) and collected a 24 h urine sample for examination of urinary tetrahydroaldosterone and aldosterone-18-glucuronide.


RESULTS
In hypokalaemic primary aldosteronism the saline infusion test showed a reasonable sensitivity (91%) and specificity (90%). However, the test failed to differentiate sufficiently between essential hypertension and normokalaemic primary aldosteronism (sensitivity 57%, specificity 90%). Similarly, urinary tetrahydroaldosterone had higher sensitivity in hypokalaemic than in normokalaemic primary aldosteronism (sensitivity 64% vs 36%, specificity 100%), whereas for aldosterone-18-glucuronide, no differences in hypo- and normokalaemic primary aldosteronism were found (sensitivity 45% and 43%, specificity 100%).


CONCLUSIONS
These data show that the saline infusion test as an established test in classical hypokalaemic primary aldosteronism is not a reliable test in the normokalaemic variant of the disease. Due to its low accuracy, determination of urinary aldosterone metabolites did not prove useful in confirming either normo- or hypokalaemic patients. We conclude from our data that these tests should not be used as confirmatory testing in the normokalaemic variant of primary aldosteronism.
Schirpenbach
Caroline
C
Medical Department II, Albert-Ludwig-University, Freiburg, Germany.
Seiler
Lysann
L
Maser-Gluth
Christiane
C
Rüdiger
Frank
F
Nickel
Christian
C
Beuschlein
Felix
F
Reincke
Martin
M
D000328:Adult; D000450:Aldosterone / Q000378:metabolism / Q000652:urine*; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D006929:Hyperaldosteronism / Q000175:diagnosis*; D006973:Hypertension / Q000175:diagnosis*; D007008:Hypokalemia / Q000175:diagnosis; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D012965:Sodium Chloride / Q000008:administration & dosage
D012965:Sodium Chloride; D000450:Aldosterone