Table of critical limits.

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 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 ML0. [1] Readers are also encouraged to review general practice guidelines. [5]

Note: Dr. Kost has made several small corrections to the table this year.

References

(1.) Kost G3. Critical limits for urgent clinician notification at U.S. medical centers. JAMA. 1990;263:704-707.

(2.) Kost GJ. Critical limits for emergency clinician notification at United States childrens hospitals. Pediatries. 1991;88:600, 597-603.

(3.) Kost GJ. Using critical limits to improve patient outcome. MLO. 1993;25(3):22-27.

(4.) Kost GJ. The significance of ionized calcium in cardiac and critical care. Availability and critical limits at U.S. medical centers and children's hospitals. Arch Pashol Lab Med. 1993;117:890-896.

(5.) Empanicpator K. Critical values: ASCP practice parameter. Am F Clin Patbol. 1997; 108:247-253.

Table of critical limits
Adults 1
Test                Units           Mean (SD)     Range
Clinical chemistry                  Low limit
Glucose             mmol/L          2.6 (0.4)    1.7-3.9
                    mg/dL            46 (7)       30-70
Potassium           mmol/L          2.8 (0.3)    2.5-3.6
Calcium             mmol/L         1.65 (0.17)  1.2.5-2.15
                    mg/dL           6.6 (0.7)    5.0-8.6
Sodium              mmol/L          120 (5)      110-137
[CO.sub.2] content  mmol/L           11 (2)        5-20
Magnesium           mmol/L         0.41 (0.16)  0.21-0.74
                    mg/dL           1.0 (0.4)    0.5-1.8
Phosphorus          mmol/L         0.39 (0.10)  0.26-0.65
                    mg/dL           1.2 (0.3)    0.8-2.0
Bilirubin           [micro]mol/L       --           --
                    mg/dL              --           --
Chloride            mmol/L           75 (8)       60-90
Osmolality          mmol/kg         250 (13)     230-280
Urea nitrogen       mmol/L             --           --
                    mg/dL              --           --
Uric acid           [micro]mol/L       --           --
                    mg/dL              --           --
CSF glucose         mmol/L          2.1 (0.6)    1.1-2.8
                    mg/dL            37 (10)      20-50
Creatinine          [micro]mol/L       --           --
                    mg/dL              --           --
lonized calcium 4   mmol/L         0.82 (0.14)  0.50-1.07
                    mg/dL          3.29 (0.56)  2.00-4.29
Lactate             mmol/L             --           --
                    mg/dL              --           --
Hematology
Hematocrit          L/L            0.18 (0.05)  0.12-0.30
Hemoglobin          g/L              66 (17)      40-120
Platelets           x[10.sup.9]/L    37 (18)      10-100
WBC count           x[10.sup.9]/L   2.0 (0.7)    1.0-4,0
PT                  s                  --           -
PTT                 s                  --           -
Fibrinogen          g/L            0.88 (0.17)  0.50.1.00
Blood gases and pH
p[CO.sub.2]         mm Hg            19 (3)        9-25
pH                                  721 (0.06)  7.00-7.35
p[O.sub.2]          mm Hg            43 (6)       30.55
                    kPa             5.7 (0.8)    4.0-7.3
Test                   Mean (SD)       Range
Clinical chemistry    High limit
Glucose               26.9 (8.0)      6.1-55.5
                       484 (144)      110-1000
Potassium              6.2 (0.4)      5.0-8.0
                    8.0 (hemalyzed)
Calcium               3.22 (0.22)    2.62-3.49
                      12.9 (0.9)     10.5-14.0
Sodium                 158 (6)        145-170
[CO.sub.2] content      40 (3)         35-50
Magnesium             2.02 (0.82)    1.03-5.02
                       4.9 (2.0)      2.5-12.2
Phosphorus            2.87 (0.48)    2.26-3.23
                       8.9 (1.5)      7.0-10.0
Bilirubin              257 (86)        86-513
                        15 (5)          5-30
Chloride               126 (12)       115-156
Osmolality             326 (18)       295-375
Urea nitrogen         37.1 (21.1)    14.3-107.1
                       104 (59)        40-300
Uric acid              773 (119)      595-892
                        13 (2)         10-15
CSF glucose           24.3 (11.4)    13.9-38.9
                       438 (206)      250-700
Creatinine             654 (380)      177-1326
                       7.4 (4.3)      2.0-15.0
lonized calcium 4     1.55 (0.19)    1.30-2.00
                      6.21 (0.76)    5.21 -8.02
Lactate                3.4 (1.3)      2.3-5.0
                      30.6 (11.7)    20.7-45.0
Hematology
Hematocrit            0.61 (0.06)    0.54-0.80
Hemoglobin             199 (27)       170-300
Platelets              910 (147)      555-1000
WBC count             37.0 (20.7)    10.0-100.0
PT                      27 (9)         14-40
PTT                     68 (33)        32-150
Fibrinogen            7.75 (2.63)    5.00-10.00
Blood gases and pH
p[CO.sub.2]             67 (6)         50-80
pH                    7.59 (0.03)    7.50-7.65
p[O.sub.2]                --             --
                          --             --
(1) Adult table modified with permission by JAMA, Vol. 263, pages
704-707, 1990.
CSF, cerebrespinel fluid; WBC, white bluod cell; PT, pruthrombin time;
PTT, partial thromboplastin time.
Qualitative critical results far adults 1 include the following: For
blood bank and immunology--incompatible crossmatch, tests positive for
syphilis (RPR ur VDRL). For microbiology and parasitology--Positive
results from Gram stain or in culture from blood, cerebrospinal fluid,
or body cavity fluid; positive India ink preparation; positive rapid
antigen detection by agglutination tests for Cryptococcus, group B
streptococci, Haemaphilius influenzae b, or Neisseria meningitidis.
positive results from acid-fast bacillus stain or culture; Salmonella,
Shigella, or Campylobacter on stool culture; presence of malarial
parasites. For clinical microscopy and urinalysis--Elevated white
blood cell count in cerebraspinal fluid; presence of malignant cells,
blasts, or microorganisms in cerebrospinal fluid or body fluids;
combination of strongly positive test results for glucose and for
ketones in urine; presence of pathologic crystals (urate, cysteine,
leucine, or tyrosisel an urinalysis. Per hematology--Listed frequently
are the presence of blasts on blood smear; new diagnosis or
findinga of leskemia; presence of sickle cells (or aplastic crisis).
Listed occasionally are plasma cells, band cells, atypical lymphocytes,
and abtarmal roticulocyta count.
(2) Children and newborn tables modified with permission by Pediatrics,
Vol. 88, pages 597-603, 1991.
CSF, cerebrospinal fluid; WBC, white bload cell; PT, prothrombin time;
PTT, partial thromboplastin time; CH, Children's Hospital; USMC,
U.S. Medical Centers.
Qualitative critical results for children 2 inclade the following: For
hematology--Presence of blasts in the blood smear; new diagnosis or
findings of leukemia; presence of drepanocytes (sickle cells); left
shift, atypical lymphocytes, or abnormal reticulocyte count; abnormal
erythrocyte indices (mean corpuscular volume, mean corpuscular
hemoglobin, mean corpuscular hemoglobin concentration). For
clinical microscopy and urinalysis--Elevated white blood cells in
cerebrospinal fluid (CSF); presence of malignant cells, blasts, or
micro-organsims in CSF or body fluids; combination of strongly positive
test results for glucose and for ketones in urine. For microbiology and
parasitology--Positive results from Gram stain or culture from blood,
CSF, or body cavity fluid; presence of malarial parasites.
Children 1
Test                Units           Mean (SD)     Range     Mean (SD)
Clinical chemistry
Glucose             mmol/L          2.6 (0.5)    1.7-3.3   24.7 (8.9)
Potassium           mmol/L          2.8 (0.3)    2.0-3.5    6.4 (0.5)
Calcium             mmol/L         1.62 (0.17)  1.25-1.87  3.17 (0.22)
Sodium              mmol/L          121 (5)      110-130    156 (5)
[CO.sub.2] content  mmol/L           11 (2)        6-18      39 (3)
Magnesium           mmol/L         0.45 (0.04)  0.41-0.49  1.77 (0.45)
Phosphorus          mmol/L         0.42 (0.16)  0.16-0.65  2.87 (0.39)
Bilirubin           [micro]mol/L       --          --       257 (68)
Chloride            mmol/L           77 (8)       70-90     121 (5)
Osmolality          mmol/kg         253 (12)     240-270    318 (10)
Urea nitrogen       mmol/L             --          --      19.6 (11.4)
Uric acid           [micro]mol/L       --          --       714 (119)
CSF glucose         mmol/L          1.7 (0.7)    1.1-2.8       --
Creatinine          [micro]mol/L       --          --       336 (212)
Ionized calcium 4   mmol/L         0.85 (0.13)  0.60-1.08  1.53 (0.11)
Lactate             mmol/L             --          --       4.1 (1.2)
Albumin             g/L              17 (5)       10-25      68 (10)
Ammonia             [micro]mol/L       --          --       109 (50)
Protein             g/L              34 (5)       30-40      95 (6)
CSF protein         mg/L               --          --      1875 (854)
Hematology
Hematocrit          L/L            0.20 (0.06)  0.10-0.30  0.62 (0.05)
Hemoglobin          g/L              69 (13)      50-100    208 (29)
Platelets           x[10.sup.9]/L    53 (25)      20-100    916 (220)
WBC count           x[10.sup.9]/L   2.1 (0.9)    0.5-3.5   42.9 (25.1)
PT                  s                  --          --        21 (6)
PTT                 s                  --          --        62 (21)
Fibringogen         g/L            0.77 (0.30)  0.20-12.0      --
Bleeding time       min                --          --      14.0 (4.0)
Blood gases and pH
p[CO.sub.2]         mm Hg            21 (6)       15-40      66 (23)
pH                  --             7.21 (0.05)  7.10-7.30  7.59 (0.04)
[pO.sub.2]          mm Hg            45 (7)       30-55     124 (25)
Test                  Range
Clinical chemistry
Glucose             13.9-55.5
Potassium            5.0-8.0
Calcium             2.74-3.74
Sodium               150-170
[CO.sub.2] content    33-45
Magnesium           1.23-3.00
Phosphorus          2.26-3.23
Bilirubin             86-342
Chloride             115-130
Osmolality           300-330
Urea nitrogen        3.9-53.6
Uric acid            595-892
CSF glucose             --
Creatinine           221-884
Ionized calcium 4   1.35-1.75
Lactate              2.4-5.5
Albumin               60-80
Ammonia               35-200
Protein               90-100
CSF protein         1000-3000
Hematology
Hematocrit          0.54-0.70
Hemoglobin           170-250
Platelets            600-1500
WBC count           15.0-100.0
PT                    15-35
PTT                   40-100
Fibringogen             --
Bleeding time        9.5-20.0
Blood gases and pH
p[CO.sub.2]           50-150
pH                  7.50-7.70
[pO.sub.2]           100-150
Newborn [1,2]
Test         Facility  Units         Mean (SD)      Range
Glucose      CH        mmol/L         1.8 (0.4)    1.1-2.8
Potassium    CH        mmol/L         2.8 (0.4)    2.5-3.7
Modified
  potassium  CH        mmol/L         2.8 (0.4)    2.5-3.7
Bilirubin    CH        [micro]mol/L      --          --
Hemoglobin   USMC      g/L             95 (35)      50-150
Hematocrit   USMC      L/L           0.33 (0.08)  0.24-0.45
[pO.sub.2]   USMC      mm Hg           37 (7)       30-50
Test          Mean (SD)      Range
Glucose      18.2 (3.6)    16.7-27.8
Potassium     7.8 (0.5)     6.5-8.0
Modified
  potassium      6.5      (See ref.3)
Bilirubin     222 (86)       86-308
Hemoglobin    223 (23)      210-250
Hematocrit   0.71 (0.04)   0.65-0.75
[pO.sub.2]     92 (12)       70-100