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Acid loading test (pH)

Definition

The acid loading test (pH) measures the ability of the kidneys to send acid to the urine when there is too much acid in the blood. This test involves both a blood test and urine test.

How the Test is Performed

Before the test, you will need to take a medicine called ammonium chloride for 3 days. Follow instructions exactly on how to take it to ensure an accurate result.

Urine and blood sample are then taken.

How to Prepare for the Test

Your health care provider will tell you to take ammonium chloride capsules by mouth for 3 days before the test.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. These soon go away.

The urine test involves only normal urination, and there is no discomfort.

Why the Test is Performed

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

Normal Results

Urine with a pH less than 5.3 is normal.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider 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 with providing a urine sample.

The risks of having blood drawn include:

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

Veins and arteries vary in size from one person 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.

References

Krapf R, Seldin DW, Alpern RJ. Clinical syndromes of metabolic acidosis. In: Alpern RJ, Moe OW, Caplan M, eds. Seldin and Giebisch's The Kidney. 5th ed. Philadelphia, PA: Elsevier; 2013:chap 59.

Sreedharan R, Avner ED. Renal tubular acidosis. In: Kliegman RM, Stanton BF, St Geme JW III, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2015:chap 529.

Review Date:10/13/2015
Reviewed By:Walead Latif DO, Nephrologist, Medical Director of Fresenius Vascular Care, and Clinical Assistant Professor of Rutgers Medical School, Newark, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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