Seated saline suppression testing for the diagnosis of primary aldosteronism: a preliminary study.
BACKGROUND
Failure of aldosterone suppression by sodium loading during fludrocortisone suppression testing (FST) or saline suppression testing (SST) confirms primary aldosteronism (PA). We previously found recumbent SST (RSST) to lack sensitivity. Aldosterone levels can be higher upright (e.g. seated) than recumbent in patients with PA and upright levels are used during FST. We therefore hypothesized that seated SST (SSST) is more sensitive than RSST, especially for posture-responsive PA.


METHODS
Of 66 patients who underwent FST (upright plasma aldosterone levels measured at 10am basally and after 4 days fludrocortisone 0.1 mg 6-hourly and oral salt loading), 31 underwent SST (aldosterone levels measured basally at 8am and after infusion of 2 L normal saline over 4h) both recumbent and seated in randomized order and at least 2 weeks apart.


RESULTS
FST confirmed PA in 23 of 31 patients (day 4 upright aldosterone level >165 pmol/L), excluded PA in three and was originally "inconclusive" in five. However, one with "inconclusive" FST had PA confirmed by lateralizing AVS and was reclassified "unilateral PA". Of 24 with confirmed PA (eight unilateral, 11 bilateral, and five undetermined subtype), 23 (96%) tested positive by SSST (4-h aldosterone level >165 pmol/L) compared with 8 (33%) by RSST (4-h plasma aldosterone level >140 pmol/L) (P < .001). RSST missed one unilateral, all bilateral, and four with as-yet undetermined subtype. RSST was positive in 7 of 10 (70%) posture-unresponsive vs one of 14 (7.1%) posture-responsive patients (P < .005).


CONCLUSIONS
These preliminary results suggest that seated SST may be superior to recumbent SST in terms of sensitivity for detecting PA, especially posture-responsive forms, and may represent a reliable alternative to FST.
Endocrine Hypertension Research Centre, University of Queensland School of Medicine, Greenslopes and Princess Alexandra Hospitals, Brisbane 4102, Australia.
Ashraf H
AH
Ahmed
Diane
D
Cowley
Martin
M
Wolley
Richard D
RD
Gordon
Shengxin
S
Xu
Paul J
PJ
Taylor
Michael
M
Stowasser
D000304:Adrenal Cortex Function Tests / Q000379:methods*; D000328:Adult; D000368:Aged; D000450:Aldosterone / Q000097:blood; D005260:Female; D005438:Fludrocortisone / Q000008:administration & dosage; D006801:Humans; D006929:Hyperaldosteronism / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011187:Posture / Q000502:physiology*; D012083:Renin / Q000097:blood; D012965:Sodium Chloride
D012965:Sodium Chloride; D000450:Aldosterone; D012083:Renin; D005438:Fludrocortisone