Eat a normal diet with a normal amount of salt, unless otherwise instructed by your doctor.
Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with test results. Certain diuretic medicines may affect test results.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
The test is usually done for patients who are severely ill with acute kidney insufficiency. The test helps determine if the drop in urine production is due to reduced blood flow to the kidney or to kidney damage itself.
What abnormal results mean
A meaningful interpretation of the test can be made only when your urine volume has dropped to less than 500 mL/day.
A FENa of less than 1% indicates decreased blood flow to the kidney, while a FENa greater than 1% (and usually greater than 3%) suggests kidney damage.
What the risks are
The urine sample has no risk. The risks of drawing blood include:
Fainting or feeling lightheaded
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Landry DW, Basari H. Approach to the patient with renal disease. In: Goldman L, Schafer AI, eds.Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 116.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Herbert Y. Lin, MD, PHD, Nephrologist, Massachusetts General Hospital; Associate Professor of Medicine, Harvard Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.