7
Table 3. Measurement of ARR: A Suggested Approach
A. Preparation: agenda
1. Attempt to correct hypokalemia.
Measure plasma potassium in blood collected slowly with a syringe and needle
[preferably not a Vacutainer to minimize the risk of spuriously raising potassium].
During collection, avoid fist clenching, wait at least 5 seconds after tourniquet
release (if used) to achieve insertion of needle, and ensure separation of plasma
from cells within 30 minutes of collection. A plasma [K
+
] of 4.0 mmol/L is the
aim of supplementation.
2. Encourage patient to liberalize (rather than restrict) sodium intake.
3. Withdraw agents that markedly affect the ARR for at least 4 weeks:
a. Spironolactone, eplerenone, amiloride, and triamterene
b. Potassium-wasting diuretics
c. Products derived from licorice root (eg, confectionary licorice, chewing
tobacco)
4. If the results of ARR after discontinuation of the above agents are not
diagnostic, and if hypertension can be controlled with relatively noninterfering
medications (see Table 5), withdraw other medications that may affect the ARR
for ≥2 weeks, such as:
a. β-Adrenergic blockers, central α-2 agonists (eg, clonidine, α-methyldopa), and
nonsteroidal anti-inflammatory drugs
b. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers,
renin inhibitors, and dihydropyridine calcium channel antagonists
5. If necessary to maintain hypertension control, commence other antihypertensive
medications that have lesser effects on the ARR (e.g. verapamil slow-release,
hydralazine [with verapamil slow-release, to avoid reflex tachycardia], prazosin,
doxazosin, terazosin). (See Table 5).
6. Establish OC and HRT status because estrogen-containing medications may
lower DRC and cause false-positive ARR when DRC (rather than PRA)
is measured. Do not withdraw OC unless confident of alternative effective
contraception.
B. Conditions for blood collection
1. Collect blood mid-morning, after the patient has been up (sitting, standing, or
walking ) for ≥2 hours and seated for 5–15 minutes.
2. Collect blood carefully, avoiding stasis and hemolysis (see A.1 above).
3. Maintain sample at room temperature (and not on ice, as this will promote
conversion of inactive to active renin) during delivery to laboratory and prior to
centrifugation and rapid freezing of plasma component pending assay.
