24-Hour Urinary Sodium Mass Concentration

Why This Test Might Be Ordered

Your doctor may recommend this test if you have symptoms like high blood pressure, swelling (edema), frequent urination, or if you’re being treated for conditions like heart failure, kidney disease, or certain types of hypertension. It can also help diagnose or monitor conditions like syndrome of inappropriate antidiuretic hormone secretion (SIADH) or hyperaldosteronism.

What to Expect Before the Test

You’ll need to collect all urine for a full 24-hour period. Typically, you’ll start by emptying your bladder at home at a set time (often morning), then collect every urine void for the next 24 hours. Store all urine in a refrigerator or cool container. Bring the entire collection to your doctor’s office or lab the next day.

What Happens During the Test

No special lab visit is needed—your urine sample is sent to a lab for analysis. The lab measures the total sodium content in your urine over the 24-hour period using specialized equipment.

What the Results Mean

Results are typically reported as the total sodium excreted in milligrams (mg) over 24 hours. Low sodium excretion may indicate kidney problems or conditions that restrict urine output, while very high levels could suggest overuse of salt or certain medications.