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Acid loading test (pH)

Definition

The acid loading test (pH) measures the ability of the kidney tubules to acidify urine when there is increased plasma acidity.

See also: Urine pH

How the Test is Performed

You'll be told to take ammonium chloride capsules by mouth for 3 days. Then, a urine and blood sample are taken. (The blood sample is needed to show that the ammonium chloride made the blood slightly acidic.) The laboratory measures the level of acid found in both samples.

For information on how the urine and blood samples are obtained, see:

How to Prepare for the Test

Your doctor will tell you to take ammonium chloride capsules by mouth for 3 days prior to the test.

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

This test is done to see how well your kidneys control the body's acid-base status.

Normal Results

Urine with a pH less than 6 is normal.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

The most common disorder associated with an abnormal result is renal tubular acidosis.

Risks

There are no risks associated with providing a urine sample.

The risks of having blood drawn include:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Review Date: 12/2/2009
Reviewed By: 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.
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