pH - urine

Alternative names
Urine pH

A urine pH test measures the pH (acidity) of urine. See also acid loading test.

How the test is performed
Collect a “clean-catch” (midstream) urine sample. To obtain a clean-catch sample, men or boys should wipe clean the head of the penis. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well. As you start to urinate, allow a small amount to fall into the toilet bowl (this clears the urethra of contaminants). Then, in a clean container, catch about 1 to 2 ounces of urine and remove the container from the urine stream. Give the container to the health care provider or assistant.

For infants, thoroughly wash the area around the urethra. Open a Urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant. For males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Place a diaper over the infant (bag and all). Check your baby frequently and remove the bag after the infant has urinated into it. For active infants, this procedure may take a couple of attempts - lively infants can displace the bag, causing an inability to obtain the specimen. The urine is drained into a container for transport back to the health care provider.

How to prepare for the test

Your health care provider may advise you to stop taking certain drugs that can affect the results of the test. Eat a normal, balanced diet for several days before the test.

Submit a urine sample to the laboratory. If the specimen is contaminated by vaginal discharge or bleeding, then collect a clean-catch sample. If the collection is being taken from an infant, a couple of extra collection bags may be necessary.

How the test will feel
The test involves only normal urination, and there is no discomfort.

Why the test is performed

pH is a measure of how acidic or alkaline a fluid is, like blood or urine. The pH in blood is maintained within the narrow range of 7.35 to 7.45. Your body maintains this narrow range by using buffers - chemicals that can switch back and forth between 2 forms, a weak acid or weak base. The buffers are only temporary “stop gaps” to avoid dramatic changes in blood pH.

Long-term correction of blood pH requires the kidneys to excrete the acid or base in urine. For example, when your blood pH is low (acidic), your kidneys react by excreting more acid in the urine. The urine pH becomes more acidic until the blood pH returns to normal.

In some cases, checking your urine pH is helpful for identifying body acid-base imbalances. In other cases, a blood pH test is needed.

Your provider may want to modify your urine pH to help prevent kidney stones. Acidic urine is associated with xanthine, cystine, uric acid, and calcium oxalate stones. Alkaline urine is associated with calcium carbonate, calcium phosphate, and magnesium phosphate stones.

Some medications are more effective in acidic or alkaline environments. For example, streptomycin, neomycin, and kanamycin are more effective in treating urinary tract infections when the urine is alkaline.

Normal Values

The normal values range from 4.6 to 8.0.

What abnormal results mean

A high urine pH (alkaline urine) may indicate:

  • Gastric suction  
  • Renal failure  
  • Renal tubular acidosis  
  • Urinary tract infection  
  • Vomiting

A low urine pH (acidic urine) may indicate:

  • Chronic obstructive pulmonary disease (e.g., emphysema)  
  • Diabetic ketoacidosis  
  • Diarrhea  
  • Starvation

The test also may be performed to investigate:

  • Alkalosis  
  • Interstitial nephritis  
  • Renal tubular acidosis - distal  
  • Sepsis

What the risks are
There are no risks.

Special considerations

  • A diet high in citrus fruits, vegetables, or dairy products can increase your urine pH. Some drugs also can increase urine pH, including acetazolamide, potassium citrate, and sodium bicarbonate.  
  • A diet high in meat products or cranberries can decrease your urine pH. Drugs that can decrease urine pH include ammonium chloride, chlorothiazide diuretics, and methenamine mandelate.  
  • Urine pH can be affected by various factors after collection. For example, leaving the urine standing in an uncovered container. Also, bacteria usually increase the pH as they break down urea to ammonia.


Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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