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.

Alternative Names

Renal tubular acidosis - acid loading 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.

Samples of urine and blood 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. This soon goes 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.

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

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

References

Dixon BP. Renal tubular acidosis. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 547.

Seifter JL. Acid-base disorders. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 104.