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Test Code LAB47 Ammonia, Blood

Performing Laboratory

St. Louis Children's Hospital - Chemistry

Specimen Requirements

SPECIMEN MUST BE RECEIVED IN LAB WITHIN 15 MINUTES OF COLLECTION

Patient Preparation: None

Container/Tube  
Preferred: Mint green-top Lithium Heparin (MNTGRN LiHep) tube
Acceptable: Lavender-top (EDTA) tube
Collection Volume: 3.0 mL (minimum 1.0 mL)
Special Instructions:

  • Specimen should be obtained from free flowing venous or arterial source without the use of a tourniquet.
  • Whole blood specimen in vacutainer (or microtainer) should be placed in wet ice immediately at bedside and delivered STAT to the laboratory - removing from the wet ice to send thru the pneumatic tube system. Specimen must be received & processed in lab within 15 minutes of collection.

NOTE: although venous or arterial sample may be placed in microtainer to be sent to lab, DO NOT collect by capillary method into microtainer.

Sample Rejection

Specimens collected by capillary method.

Specimens collected in red-top tubes.

Specimens that are grossly hemolyzed.

Mislabeled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 2 hours from receipt in performing lab

Reference Values

Reference Intervals:

< 2 months: ≤ 90 mcmol/L                    
≥ 2 months: ≤ 50 mcmol/L                                                                      

Critical Values: >200 mcmol/L (applies to all ages)

Critical test results will automatically be called back initially and every 24 hours thereafter

Methodology

Enzymatic with Glutamate dehydrogenase (GLDH)

Limitations

  • Cefoxitin and Intralipid cause artificially high and low ammonia results respectively at the therrapeutic drug level. Temozolomide at therapeutic concentrations may lead to erroneous results.
  • In vary rare cases gammopathy, in particular IgM (Waldenstrom's macroglobulinemia), may cause unreliable results.

For diagnostics purposes, the results should always be assessed in conjunction with the patient's medical history, clinical examination, and other findings.

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Immediately centrifuge specimen in a refrigerated centrifuge to separate and place prcessed sample in wet ice. If specimen is collected in a Lavender-top (EDTA) tube; aliquot sample into a Roche false bottom tube for testing (labeling with specimen type - EDTA plas)
Processed Volume: 0.3 mL plasma/serum
Analyte Stability:

Specimen Type Temperature Time
Whole Blood (unprocessed)  Ambient 15 minutes
Plasma (processed) Refrigerated/on ice (preferred)    3 hours
  Ambient  30 minutes
  Frozen  2 weeks 

 

Test Classification and CPT Code

82140

LOINC

16362-6

Last Reviewed

06/2025