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

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:

• Clean catch urine collection
• Venipuncture (blood draw)

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

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.

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

Strongly acidic urine of less than pH 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.

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

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.