Phenolphthalein Test (Laxative Abuse Test)

Norm of Phenolphthalein Test (Laxative Abuse Test)



Usage of Phenolphthalein Test (Laxative Abuse Test)

Anorexia nervosa (laxative use for weight loss), chronic self-prescribed laxative use, and unexplained diarrhea.


Description of Phenolphthalein Test (Laxative Abuse Test)

The phenolphthalein test is a toxicologic screening for evidence of recent laxative use. Phenolphthalein is the active ingredient of many over-the-counter laxative preparations. It causes stool evacuation by enhancing fluid and electrolyte accumulation in the intestines. After ingestion, phenolphthalein is excreted in both the feces and the urine and is detectable for up to 32 hours. It may also have laxative effects for up to 4 days and cause fluid and electrolyte abnormalities. This test is performed on an aliquot of a 24-hour urine sample to detect the presence of phenolphthalein by thin-layer chromatography.


Professional Considerations of Phenolphthalein Test (Laxative Abuse Test)

Consent form NOT required.

  1. Preschedule this test with the laboratory.
  2. Obtain a clean, 3-L container without preservative.
  3. Write the beginning time of collection on the laboratory requisition.



  1. Discard the first morning urine specimen.
  2. Begin to time a 24-hour urine collection.
  3. Save all the urine voided for 24 hours in a refrigerated, clean, 3-L container. Document the quantity of urine output during the specimen collection period. Include the urine voided at the end of the 24-hour period. For catheterized clients, keep the drainage bag on ice and empty the urine into the collection container hourly.


Postprocedure Care

  1. Compare the urine quantity in the specimen container with the urinary output record for the test. If the specimen contains less urine than what was recorded as output, some of the sample may have been discarded, thus invalidating the test.
  2. Document the quantity of urine output and the ending time for the 24-hour collection period on the laboratory requisition.
  3. Send the entire 24-hour urine specimen to the laboratory for testing. The test is performed on a 20-mL aliquot of the 24-hour specimen.


Client and Family Teaching

  1. Save all the urine voided in the 24-hour period and urinate before defecating to avoid loss of urine. If any urine is accidentally discarded, discard the entire specimen and restart the collection the next day.
  2. Results are normally available within 24 hours.
  3. Discuss psychologic and rehabilitation services if laxative abuse is determined.


Factors That Affect Results

  1. Repeating the collection on consecutive days for a total of three 24-hour specimens increases the likelihood of detecting laxative abuse.


Other Data

  1. Methods are available to test for a wide range of laxative ingredients in urine.
  2. Complications of laxative abuse may include diarrhea, abdominal pain, hypokalemia, hypermagnesemia, cathartic colon, and the development of ammonium urate renal calculi.