Plasma Renin Activity
(PRA)

Sample type

Frozen plasma (EDTA)

Uses

Particularly useful to diagnose curable hypertension (e.g., primary aldosteronism, unilateral,renal artery stenosis)
May help differentiate patients with volume excess (e.g., primary aldosteronism)
In children with salt-losing form of congenital adrenal hyperplasia due to 21-hydroxylase

deficiency, severity of disease is related to degree of increase. PRA level may serve as

PRA level may serve as guide to adequate mineralocorticoid replacement therapy.

Precautions

Plasma should be frozen -

patient should be taken off medications for at least three weeks prior to sample collection.
Dietary sodium levels during the period prior to testing can affect renin levels. Sodium restriction tends to cause an increase in renin activity, while supplementation can result in lower values.
A 24-hour urine sodium determination from a sample collected on the day before a renin test can be used to assess sodium intake.
Since patient posture prior to collection affects renin levels, it is recommended that the patient be ambulatory for at least 30 minutes before blood collection. If inpatients are physically able, they should be asked to ambulate for 30 minutes before blood is drawn for renin activity.

Interfering factors

Transition to upright posture causes a reduction in renal perfusion pressure and an increase in PRA.
PRA levels exhibit a diurnal rhythm, with the highest levels observed in the early morning upon awakening and falling during the day.
Collecting blood for PRA and aldosterone at midmorning from seated patients following a two to four hour upright posture improves the sensitivity of the aldosterone renin (ARR) for primary aldosteronism.
PRA levels can be increased by dietary salt restriction and suppressed by consumption of a high salt diet.
PRA levels gradually fall as renal function declines with normal aging or with the development of renal impairment due to reduced renin-producing capacity and salt-retention.
Some medications can interfer with plasma renin level such as: Diuretics, Dihydropyridine calcium channel blockers, Angiotensin converting enzyme (ACE) inhibitors, Angiotensin receptor antagonists, Beta-blockers, Clonidine, Alpha-methyldopa,and Nonsteroidal anti-inflammatory agents.

Pre-analytical errors

1-Non-frozen sample received,non-separated sample received,non-EDTA plasma specimen, gross icterus,and unlabeled specimen

2-The patient’s history has not been taken carefully and therefore there is information that needs to know and is not available.

The corrective actions

1-The sample must be rejected and another sample will be requested.

2-You must communicate with the patient and know all the informations you need. And next time the history of the patient should be taken carefully.

Post-analytical errors

1-Writing a wrong result or wrong name in the report

2-report were sent to incorrect patient

The corrective action

1-If the report is not delivered to the patient and this error is discovered, the correct result or the correct name must be written, but if the report is delivered to the patient, you must communicate with the patient, apologise to him, and tell him that an error has occurred and replace it with the correct report.

2-Communicate with patient ,apologizing for the error, and providing him with the correct report

Reference range

0-11 months: 2-37 ng/ml/hour

1-3 years: 1.7- 11.2 ng/ ml/hour

4-5 years: 1.0-6.5 ng/ml/hour

6-10 years: 0.5-5.9 ng/ml/hour

11-15 years: 0.5-3.3 ng/ml/hour

> 15 years: 0.16-5.3 ng/ml/hour

Normal values depend on the laboratory and the patients prevailing Na and K, status of hydration,and posture.

Only stimulated values are of practical value in evaluating hypertensive patients.