Table of critical limits - Clinical and Professional Reference Guides - Illustration

Medical Laboratory Observer, August, 2003

Critical limits define the boundaries of the life-threatening values of laboratory test results. Critical results, also called critical values, are those that fall outside the high and low critical limits. Urgent clinician notification of critical results is a responsibility of the laboratory. The system of critical value reporting was first implemented in a hospital by George D. Lundberg, MD, and first published in MLO in 1972.

The tables presented here are based on three national surveys by Gerald J. Kost, MD, PhD, of the University of California, Davis, Health System. Adapted with permission from his articles, (1-4) the tables summarize the critical limits used by 92 responding U.S. medical centers, including 20 trauma centers, and 39 responding children's hospitals. Mean and standard deviation (SD) data are presented. The frequency with which critical limits were listed can be found in the original articles.

As a rule of thumb, the "mean low" and "mean high" figures may be considered the critical limits for each test listed. Each institution should establish its own set of critical limits and clinician notification policy.

Dr. Kost conducted an independent national survey of U.S. medical centers and children's hospitals to determine ionized calcium critical limits. (4) His extensive overview of critical limits and patient outcomes appeared in the March 1993 issue of MLO. (1) Readers are also encouraged to review general practice guidelines. (5)