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Test Code LAB4010 AMMONIA

Important Note

Useful for:

  • Assisting in the diagnosis of hepatic coma and hepatic encephalopathy in terminal stages of liver cirrhosis, heaptic failure, acute and subacute necrosis and Reye syndrome.

  • Investigating and monitoring treatment for inborn errors of metabolism (defects in the urea cycle and organic acids).

  • Cases of unexplained lethargy and vomiting, encephalopathy, or any neonate with unexplained neurologic deterioration. 

This test should not be used to assess the degree of dysfunction

Specimen Type

Preferred Sample: EDTA Plasma (Lavender Top Tube) ON ICE

Alternate Sample: Lithium Heparin Plasma (Light Green Top Tube) ON ICE **

 

**Lithium heparin samples cannot be stored frozen and have a maximum stability of 2 hours.

Collection Instructions

Inpatient Collection: 

Collection tube must be completely filled. Place tube immediately on wet ice and transport to Lab STAT.

 

Outpatient Collection: 

Collection tube must be completely filled. Specimen should be spun, aliquoted and frozen for transport to the laboratory. 

 

Processing Instructions

Specimen must be spun in refrigerated centrifuge and run immediately after.

Sample Stability

EDTA Plasma:

Refrigerated: 2 hours
Frozen: 3 weeks

Lithium Heparin:

Refridgerated: 2 hours

 

Cannot be frozen

Rejection Criteria

Sample must be placed on wet ice immediately. Ammonia must be drawn in separate tube, cannot be combined with any other test using same container. Results may be affected if tube is not completely filled.

 

Results for short drawn tubes should be released with the following comment:

“This specimen did not meet Kootenai Health’s guidelines for the recommended collection volume. Interpret results with caution. Recommend redraw if results do not correlate with patient’s medical history and/or clinical examination.”

 

Clinical Information

Ammonia is produced from the breakdown of animo acids and from the action of intestinal bacteria on dietary protein. Ammonia is converted to urea in the liver, thus making it non-toxic. Excess ammonia has a toxic effect on the central nervous system. Clinical manifestations are usually neurological disturbances. Severe liver failure from Reye’s Syndrome, viral hepatitis, or cirrhosis result in elevated ammonia levels. Genetic defects in the urea cycle and some other hereditary disorders can cause hyperammonemia. Elevated ammonia levels have also been reported due to the administration of valproic acid.

Method

Enzymatic/Glutamate Dehydrogenase

 

Glutamate dehydrogenase (GLDH) allows ammonia to bind with α-ketoglutarate and NADH to yield glutamate and NAD+. Ammonia concentration in the plasma is proportional to the decrease in absorbance (NADH to NAD+) at 340 nm. The reagent also contains lactate dehydrogenase in excess to reduce endogenous pyruvate from interfering with the assay system.

Limitations

  • Levels increase rapidly as specimen sits at room temperature.
  • Instrument absorbance errors were observed when the intralipid concentrations were greater than 100 mg/dL.
  • Sulfasalazine and its metabolite Sulphapyridine at therapeutic concentrations may lead to falsely low results.
  • Atmospheric ammonia may falsely elevate results
  • Anticoagulants with ammonia ions may falsely elevate results
  • Ammonia is not always elevated in patients with urea cycle disorders
  • High protein diets may falsely elevate levels
  • GI hemorrhage may elevate levels
  • Prolonged tourniquet time can falsely elevate levels
  • Temozolomide and its metabolite MTIC may lead to falsely elevated results, and its metabolite AIC may lead to falsely low results.

Specimen Volume

Preferred: 4 mL (Completely filled)

Minimum: 1.0mL microtainer (Completely filled)

Reference Ranges

Ammonia, µmol/L
0-14 Days 56.00 - 92.00
14 Days - 28 Days 64.00 - 107.00
28 Days - 11 Years 21.00 - 50.00
11 - 19 Years 10.00 - 37.00
>19 Years 18.00 - 72.00

Test Components

Ammonia, µmol/L.

Measuring Range 13.50 µmol/L – 997.90 µmol/L

Reporting Limits 13.50 µmol/L – 1846.12 µmol/L

Turnaround Time

STAT: 1 hour
Routine: 4 hours

Test Schedule

Daily and STAT

CPT Codes

82140

LOINC Code

16362-6

IMO Code

IMO-PROC-30163791