Diagnosis
8
C. Factors to take into account when interpreting results (see Table 2)
1. Age: in patients aged >65 years, renin can be lowered more than aldosterone by
age alone, leading to raised ARR.
2. Gender: premenstrual, ovulating females have higher ARR levels than age-
matched men, especially during the luteal phase of the menstrual cycle, during
which false positives can occur, but only if renin is measured as DRC and not as
PRA.
3. Time of day, recent diet, posture, and length of time in that posture
4. Medications
5. Method of blood collection, including any difficulty doing so
6. Level of potassium
7. Level of creatinine (renal failure can lead to false-positive ARR)
Adapted from J. W. Funder et al: Case detection, diagnosis, and treatment of patients with primary
aldosteronism: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab.
2008;93:3266–3281, with permission. © Endocrine Society.
Table 3. Measurement of ARR: A Suggested Approach
(cont'd)
Table 4. ARR Cutoff Values, Depending on Assay and Based
on Whether PAC, PRA, and DRC Are Measured in
Conventional or Système International (SI) Units
PRA,
ng/mL/h
PRA,
pmol/L/min
DRC,
mU/L
a
DRC,
ng/L
a
PAC (as ng/dL) 20 1.6 2.4 3.8
30
b
2.5 3.7 5.7
40 3.1 4.9 7.7
PAC (as pmol/L)
750
b
60 91 144
1000 80 122 192
a
Values shown are on the basis of a conversion factor of PRA (ng/mL/h) to DRC (mU/L) of 8.2.
DRC assays are still in evolution, and in a recently introduced and already commonly used automated
DRC assay, the conversion factor is 12. It should be noted that there is poor correlation between
DRC and PRA in the range where PRA is <1 ng/mL/h, the domain of major interest in PA screening.
b
e most commonly adopted cutoff values are 30 for PAC and PRA in conventional units
(equivalent to 830 when PAC is in SI units) and 750 when PAC is expressed in SI units (equivalent
to 27 in conventional units).
Adapted from J. W. Funder et al: Case detection, diagnosis, and treatment of patients with primary
aldosteronism: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab.
2008;93:3266 –3281. with permission. © Endocrine Society.
