Diagnosis
10
Table 6. PA Confirmatory Tests
Test and Procedure Interpretation
Oral sodium loading test
• Patients should increase their sodium intake
to>200 mmol (~6 g )/d for 3 d, verified by
24-h urine sodium content.
• Patients should receive adequate slow-release
potassium chloride supplementation to
maintain plasma potassium in the normal
range.
• Urinary aldosterone is measured in the 24-h
urine collection from the morning of day 3
to the morning of day 4.
• PA is unlikely if urinary aldosterone
is <10 µg/ 24 h (28 nmol/d) in the
absence of renal disease where PA may
coexist with lower measured urinary
aldosterone levels.
• Elevated urinary aldosterone excretion
(>12 µg/24 h [>33 nmol/d] at
the Mayo Clinic; >14 µg/24 h [39
nmol/d] at the Cleveland Clinic)
makes PA highly likely.
SIT
Patients stay in the recumbent position for at
least 1 h before and during the infusion of 2 L
of 0.9% saline IV over 4 h, starting at 8–9:30
AM. Blood samples for renin, aldosterone,
cortisol, and plasma potassium are drawn at
time zero and after 4 h, with BP and heart rate
monitored throughout the test. In a modified
approach, which appears (in preliminary
studies) to have much higher sensitivity for
diagnosing PA, patients remain in a seated
position for ≥30 min and during the infusion.
Postinfusion plasma aldosterone levels
<5 ng/dL (140 pmol/L) make the
diagnosis of PA unlikely, whereas levels
>10 ng/dL (280 nmol/L) are a sign of
very probable PA. Values between 5 and
10 ng/dL are indeterminate, although a
cutoff of 6.8 ng/ dL (190 pmol/L) has
been found to offer the best trade-off
between sensitivity and specificity.
For the seated SIT, a postinfusion
plasma aldosterone of >6 ng/dL (170
pmol/L) confirms PA, provided plasma
cortisol concentration is lower than
the value obtained basally (to exclude a
confounding ACTH effect).
FST
Patients receive 0.1 mg oral fludrocortisone
every 6 h for 4 d, together with slow-release
KCl supplements (every 6 h at doses sufficient
to keep plasma K+, measured four times a
day, close to 4.0 mmol/L), slow- release NaCl
supplements (30 mmol three times daily with
meals) and sufficient dietary salt to maintain
a urinary sodium excretion rate of at least
3 mmol/kg body weight. On day 4, plasma
aldosterone and PRA are measured at 10 AM
with the patient in the seated posture, and
plasma cortisol is measured at 7 and 10 AM.
Upright plasma aldosterone >6 ng/dL
(170 nmol/L) on day 4 at 10 AM
confirms PA, provided PRA is
<1 ng/mL/h and plasma cortisol
concentration is lower than the value
obtained at 7 AM (to exclude a
confounding ACTH effect).
