Urinary ammonium testing

Answers from the Lab

Accurately measuring and understanding a patient's urinary ammonium levels is critically important to determining the underlying causes of metabolic acidosis, as well as assessing and managing patients with calcium kidney stones.

Historically, nephrologists have attempted to measure urinary ammonium levels by using a commonly accepted testing method known as the urine anion gap, which subtracts the urine concentration of chloride (anions) from the concentrations of sodium plus potassium to estimate the number of ions in a patient’s urine.

The problem is that these measurements often do not give nephrologists a true representation of a patient’s urinary ammonium levels in the differential diagnosis of metabolic acidosis. 

Or, as John Lieske, M.D., medical director of Mayo Clinic’s Renal Testing Laboratory in Rochester, Minnesota, tells Kidney News Online: “We know urinary anion gap doesn't work.”

What does work, Dr. Lieske says, are testing methods offered by Mayo Clinic Laboratories that directly measure urinary ammonium levels to give nephrologists a better and more accurate understanding of a patient’s true urinary ammonium level. “It’s something that we have offered for at least 10 years, probably more, here in the renal lab (at Mayo Clinic),” Dr. Lieske says. “And I would say from a lab technology viewpoint, it’s not that hard to do. It's really a matter of demand.”

Offered as part of a 24-hour urinary super saturation profile or in random outpatient urine testing situations, Mayo Clinic Laboratories’ direct urinary ammonium testing takes the guesswork out of determining a patient’s acid base disorder.

“The interpretation (between direct and anion gap testing) is quite similar,” Dr. Lieske says. “The big difference is with direct ammonium testing, you're actually getting the right number, while with the urine anion gap the numbers may not reflect what is actually going on. Thus, directly measuring urine ammonium would be a more reliable way to get the desired piece of data..”

You can listen to Dr. Lieske talk more about the direct urinary ammonium testing offered by Mayo Clinic Laboratories in this test specific episode of the “Answers From the Lab" podcast.

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Useful information

  • Diagnosis of the cause of acidosis
  • Diagnosis and treatment of kidney stones

Specimen requirements

AMMO | Ammonium, 24 Hour, Urine


  • Aliquot Tube, 5 mL (T465)
  • Diazolidinyl Urea (Germall) 5.0 mL (T822)

Container/Tube: Plastic vial

Specimen Volume: 4 mL

Collection Instructions:

  • Add 5 mL of diazolidinyl urea (Germall) as preservative at start of collection or refrigerate specimen during and after collection.
  • Collect urine for 24 hours.
  • Aliquot urine into plastic vial.
  • Specimens with pH >8 may indicate bacterial contamination and testing will be cancelled. Do not attempt to adjust pH as it will adversely affect results.

Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens in Special Instructions for multiple collections.

RAMBO | Ammonium, Random, Urine

Supplies: Aliquot Tube, 5 mL (T465)

Container/Tube: Plastic tube

Specimen Volume: 4 mL

Collection Instructions:

  • Collect a random urine specimen.
  • No preservative.

Performance information

AMMO | Ammonium, 24 Hour, Urine

Analytic time: Same day/1 to 2 days

Days performed: Monday through Sunday

RAMBO | Ammonium, Random, Urine

Analytic time: Same day to 2 days

Days performed: Monday through Sunday

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Cory Pedersen

Cory Pedersen is a senior marketing specialist for Mayo Clinic Laboratories.