Test Catalog

Test ID: RAMBO    
Ammonium, Random, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of the cause of an acidosis

 

Diagnosis and treatment of kidney stones

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

The kidney regulates acid excretion and systemic acid base balance. Changing the amount of ammonium in the urine is one important way the kidneys accomplish this task. Thus, measuring the urine ammonium level can provide understanding of the cause of an acid base disturbance in individual patients.(1-3)

 

The urine ammonium level can also provide a lot of information about the daily acid production in a given patient. Since most of an individual's acid load comes from ingested protein, the urine ammonium is a good indicator of dietary protein intake.

 

Urine ammonium measurements can be particularly helpful for the diagnosis and treatment of kidney stone patients:

-High urine ammonium and low urinary pH suggests ongoing gastrointestinal losses. Such patients are at risk of uric acid and calcium oxalate stones.

-Low urine ammonium and high urine pH suggests renal tubular acidosis. Such patients are at risk of calcium phosphate stones.

-Patients with calcium oxalate and calcium phosphate stones are often treated with citrate to raise the urine citrate (a natural inhibitor of calcium oxalate and calcium phosphate crystal growth). However, since citrate is metabolized to bicarbonate (a base) this drug can also increase the urine pH. If the urine pH gets too high with citrate treatment, one may unintentionally increase the risk of calcium phosphate stones. Monitoring the urine ammonium is one way to titrate the citrate dose and avoid this problem. A good starting citrate dose is about one-half of the urine ammonium excretion (in mEq of each). One can monitor the effect of this dose on urine ammonium, citrate, and pH values, and adjust the citrate dose based upon the response. A fall in urine ammonium should indicate whether the current citrate is enough to partially (but not completely) counteract the daily acid load of that given patient.(4)

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Random: 3-65 mmol/L

No reference values established for <18 years and >77 years of age.

Interpretation Provides information to assist in interpretation of the test results

If a patient has an acidosis, and the amount of ammonium in the urine is low, this suggests a renal tubular acidosis. If the amount of ammonium is high, this suggests that the kidneys are working normally and that there are other losses of bicarbonate in the body. Typically this implies gastrointestinal losses.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Peonides A, Levin B, Young W: The renal excretion of hydrogen ions in infants and children. Arch Dis Child 1965 February;40(209):33-39

2. Kamel KS, Briceno LF, Sanchez MI, et al: A new classification for renal defects in net acid excretion. Am J Kidney Dis 1997 Jan;29(1):136-146

3. Madison LL, Seldin DW: Ammonia excretion and renal enzymatic adaptation in human subjects, as disclosed by administration of precursor amino acids. J Clin Invest 1958 November;37(11):1615-1627

4. Coe FL, Evan A, Worcester E: Pathophysiology-Based Treatment of Idiopathic Calcium Kidney Stones. Clin J Am Soc Nephrol 2011 Aug;6(8):2083-2092