Magnesium Urine Test in California

What this test measures

The kidneys filter magnesium and then reabsorb most of it, adjusting the amount excreted to keep body levels steady. A urine magnesium measurement can therefore show whether the kidneys are holding onto magnesium appropriately or losing more than expected. It may be collected as a random sample or as a timed collection, most often over a full day.

For a timed collection, all urine produced during the collection period is saved and the total volume is measured. The laboratory reports the magnesium concentration and, when a timed collection is used, the total amount excreted. Calculating the fractional excretion of magnesium requires comparing urine and serum values along with creatinine, so paired samples are sometimes ordered.

Providers order this test when magnesium imbalance is suspected and they need to understand the kidney's role. It can help distinguish between low intake or digestive losses and kidney wasting. Results are interpreted with serum magnesium, kidney function, medicines, and the clinical picture. A qualified healthcare provider should explain what the findings mean.