Download Plasma Renin Activity (PRA)

Plasma Renin Activity (PRA)
Clinical Use
• Assess renin-aldosterone axis
• Differential diagnosis of hypertension
Clinical Cut-off Values††
Sodium/volume hypertension likely
Primary aldosteronism
possible§
Renin-mediated hypertension likely
Renovascular hypertension possible
Renovascular hypertension more likely
ng/mL/h
0.3-3.0
0.4-8.8
0.65-5.0
Upright
–
–
<15.0
<17.0
<16.0
<16.0
<0.65
<0.65
>0.65
>1.5
>10.0
Clinical Background
Renin is a proteolytic enzyme produced
by the kidney. Secretion is modulated
by changes in renal blood flow. Erect
posture, sodium depletion, hemorrhage, and low cardiac output all
increase renin secretion by reducing
flow.
The measurement of plasma renin
activity (PRA) is useful in evaluating
hypertension. Primary hyperaldosteronism is associated with sodium
retention, increased blood volume,
increased renal blood flow, and low
PRA. Thus, a normal or high PRA rules
out primary aldosteronism. Conversely,
a normal or low PRA helps rule out
renal hypertension. Additionally, an
elevated PRA may indicate renovascular
hypertension due to renal artery
stenosis.
The interpretation of PRA values is
facilitated by measurements of
aldosterone and serum potassium
levels.
Renin Aldosterone Potassium
1° aldosteronism
Low
Hyporeninemic
Low
hypoaldosteronism
*In apparently healthy, non-hypertensive,
non-medicated, non-pregnant individuals
on unrestricted diets.
†Pediatric data from J Pediatr. 1976;89:256;
Pediat Res. 1979;13:817; and Eur J Pediatr.
1994;153:284.
††
In ambulatory, briefly seated hypertensive
patients.
§To be used in conjunction with aldosterone
concentration; this is a rare condition.
High
Low
Low
High
Method
• Angiotensin I generation, radioimmunoassay (RIA)
• Analytical sensitivity: 0.37 ng/mL/h
Specimen Requirements
3 mL frozen EDTA plasma
Interpretive Information
• Renal hypertension
• Addison’s disease
• Secondary hypoaldosteronism
• Medications (eg, diuretics,
ACE inhibitors)
0.4 mL minimum
Avoid refrigerated temperatures. When
submitting catheterization studies,
retain a portion of each sample at the
referring laboratory.
• Hyporeninemic hypoaldosteronism
• Primary aldosteronism
• Essential hypertension (1/3rd
of cases; PRA <0.65 ng/mL/h)
Patient preparation: moderate sodium
diet; ambulatory for 30 minutes; no
medications, preferably for 3 weeks
prior to sample collection.
137
Alphabetical Test
Section
Reference Range
Adults*
ng/mL/h
Supine
Upright
Upright/sitting
Supine
Children†
3-12 mo
<15.0
1-3 y
<10.0
4-6 y
<7.5
7-9 y
<5.9
10-12 y
<5.3
13-15 y
<4.4
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