Measurement of renin activity is useful in the differential diagnosis of individuals with hypertension. Renin levels will be elevated in patients with hypertension due to renal artery stenosis (ie, renovascular hypertension). Measurement of renin activity can also be useful in the diagnosis of primary aldosteronism. Patients with secondary aldosteronism tend to have low renin levels. Renin can also be used to assess the adequacy of steroid substitution in patients with adrenal insufficiency. Renin activity will be normal in patients with adequate supplementation and will be elevated when steroid substitution is inadequate.

• Dietary sodium levels during the period prior to testing can affect renin levels.
• 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. 

Lavender (EDTA), 4mL

• Draw blood into an EDTA tube
• Immediatley following collection, mix sample thoroughly by gentle inverting 8 - 10 times, to prevent clotting
• The patient's posture at the time of collection should be noted (see Patient Preparation)
• Keep tube at room temperature

• Centrifuge at room temperature
• Transfer plasma to a Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp), labelled as EDTA plasma
• Freeze immediately and maintain frozen until tested
  • It is critical that the plasma be transferred and frozen as quickly as possible to prevent cryoactivation of protein to renin, which results in falsely elevated renin levels

Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp)

The patient's posture at the time of collection should be noted.

Frozen (strict) - 14 days

Refrigerated - NO

Ambient - NO

• Non-frozen sample received
• Non-separated sample received
• Non-EDTA plasma specimen
• Gross icterus 

The renin in plasma is allowed to act on the plasma's endogenous substrate, angiotensinogen producing angiotensin I. This is measured by liquid chromatography/mass spectrometry (LC/MS-MS).

    0 - 11 mo: 2.000−37.000 ng/mL/hr
    1 - 3 yr:    1.700−11.200 ng/mL/hr
    4 - 5 yr:    1.000−6.500 ng/mL/hr
    6 - 10 yr:   0.500−5.900 ng/mL/hr
  11 - 15 yr:   0.500−3.300 ng/mL/hr
>15 yr:         0.167−5.380 ng/mL/hr

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. Expected renin activity levels for various levels of urinary sodium excretion are provided. Renin activity determination without the concurrent urine sodium measurement can still provide useful information if the clinician verifies that the patient has been on a normal sodium diet.

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. Reference intervals are provided for patients who have ambulated for at least 30 minutes prior to collection (upright patients). Reference intervals are also provided for patients on a normal sodium diet who are unable to ambulate (supine patients).