Definition of Acid loading test (pH):

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:

• Clean catch urine collection
• Venipuncture (blood draw)

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.