Q&A column

Overall, plasma ammonia’s sensitivity to temperature and time elapsed since collection are the major considerations when evaluating ammonia concentration in blood.^9-11

1. Green A. When and how should we measure plasma ammonia? Ann Clin Biochem. 1988;25(pt 3):199–209.
2. Barsotti RJ. Measurement of ammonia in blood. J Pediatr. 2001;138(1 suppl):S11–S20.
3. Smith LD, Garg U. Urea cycle and other disorders of hyperammonemia. In: Garg U, Smith LD, eds. Biomarkers in Inborn Errors of Metabolism: Clinical Aspects and Laboratory Determination. Elsevier; 2017:103–123.
4. Hawke L. Ammonia (plasma, blood). Association for Clinical Biochemistry and Laboratory Medicine. Feb. 1, 2012. www.acb.org.uk/our-resources/science-knowledge-hub/analyte-monographs.html
5. Huizenga JR, Tangerman A, Gips CH. Determination of ammonia in biological fluids. Ann Clin Biochem. 1994;31(pt 6):529–543.
6. Dorwart WV, Saner M. Heparinized plasma is an unacceptable specimen for ammonia determination. Clin Chem. 1992;38(1):161.
7. da Fonseca-Wollheim F, van Dam M. Interference by heparin in enzymatic determination of plasma ammonia depends on reagent composition. Clin Chem. 1992;38(9):1921–1922.
8. Mousli S, Wakid NW. Ammonia production during clot retraction and its use in assay of fibrinoligase. Clin Chem. 1977;23(9):1739–1743.
9. Lindner A, Bauer S. Effect of temperature, duration of storage and sampling procedure on ammonia concentration in equine blood plasma. Eur J Clin Chem Clin Biochem. 1993;31(7):473–476.
10. Lowe WC. Freezing as a method of preserving blood ammonia. Clin Chem. 1968;14(11):1074–1079.
11. da Fonseca-Wollheim F. Preanalytical increase of ammonia in blood specimens from healthy subjects. Clin Chem. 1990;36(8 pt 1):1483–1487.

Sridevi Devaraj, PhD, DABCC
Medical Director, Clinical Chemistry and Point of Care Technology
Texas Children’s Hospital and Pavilion for Women
Professor, Pathology and Immunology
Baylor College of Medicine
Houston, Tex.
Member, CAP Clinical Chemistry Committee

Izmarie Poventud-Fuentes, PhD
Fellow, Clinical Chemistry
Baylor College of Medicine
Houston, Tex.

Q. Is there a requirement to notify nursing personnel or doctors about each critical value obtained for a patient after the initial occurrence of the critical result?

A.CAP checklist requirement COM.30000 Critical Result Notification defines critical results as test results that may require rapid clinical attention to avert significant patient morbidity or mortality. Each laboratory may define its own critical values and critical results that pertain to its patient population. A laboratory may also establish different critical results for specific patient subpopulations (e.g. dialysis clinic patients, oncology patients, newborns). The policy may also define additional rules for critical result notification, such as notifications needed for additional critical test results obtained on a patient after an initial occurrence. Policies for reporting critical results should be approved by the laboratory director and allow for prompt patient-management decisions.

The CAP recommends that laboratories develop critical values and result notification policies in consultation with clinicians since clinicians are strongly discouraged from opting out of receiving critical result notifications. Developing clear-cut policies, coupled with educating staff about those policies, is the key to success.

Clinical and Laboratory Standards Institute. GP47: Management of Clinical- and Significant-Risk Results, 1st ed.; 2015.

Standard: Test Report. 42 CFR §493.1291(g). https://j.mp/CLIA_493-1291g

Trudy R. Darden, MA, MT(ASCP)
Manager, Accreditation Services
CAP Accreditation Programs
College of American Pathologists
Northfield, Ill.