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Acid loading test (pH)

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.

A urine and blood sample are then taken.

How to Prepare for the Test

Your 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.

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 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.


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 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.


McPherson RA, Ben-Ezra J. Basic examination of urine. In: McPherson RA, Pincus MR, eds.Henry's Clinical Diagnosis and Management by Laboratory Methods

Seifter JL. Acid-base disorders. In: Goldman L, Schafer AI, eds.Goldman's Cecil Medicine

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Update Date 11/5/2013

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