Serum or Plasma Free Fraction of Free Midregional Pro-Atrial Natriuretic Peptide (MR-ProANP)

What This Test Measures

MR-ProANP is a precursor fragment of atrial natriuretic peptide (ANP), a hormone produced by the heart’s atria when they stretch due to excess fluid. The free fraction of this peptide reflects how much is actively circulating in your bloodstream. This test specifically measures the unbound (free) portion, which can be more sensitive for detecting early changes in heart function.

Why It’s Done

Your doctor may order this test if you have symptoms like shortness of breath, swelling, or high blood pressure, or if you’re being evaluated for conditions like heart failure, fluid overload, or certain kidney or liver diseases. It can also help monitor treatment responses in patients with chronic heart conditions.

How It Works

Blood is drawn and processed to separate serum or plasma from blood cells. The free MR-ProANP fragment is then measured using a sensitive immunoassay technique, which detects its presence and concentration in your blood.

What to Expect

You’ll typically have a small needle inserted into a vein (usually in your arm) to collect blood. The process takes about 5 minutes, and you may feel a slight pinch. Afterward, you can resume normal activities, though you may experience mild bruising or soreness at the site.