Critical values are potentially life-threatening laboratory results that must be conveyed immediately to the physician or other health care professional so that therapeutic measures can be instituted rapidly. Main Line Health Laboratories (MLHL) maintains critical values for routine laboratory studies, therapeutic drug monitoring, microbiology testing and blood bank results.

When a critical value is encountered, MLHL automatically repeats the test in question. Once the critical value is verified, we will report the value to your office, usually by telephone. If an answering service is reached, we will inform them that you have a critical laboratory result, provide the patient's name and request that you contact our testing facility. If your answering service is authorized to accept critical values, the result will be left with the service. Communication of critical values is documented on the patient's laboratory report. If your office uses an answering machine after the close of business and no physician can be reached, MLHL will leave critical results on the answering machine and follow up the next working day.

Critical values for general laboratory tests

Test Low ( < or = ) High ( > or = )
Hemoglobin 7 g/dl 20 g/dl
White cell count 2500/ mm3  30,000/mm3 *
Platelet count 50,000/mm3
100,000/mm3 (NICU)
1,000,000/mm3 
Fibrinogen 100 mg/dl None
Prothrombin Time None INR 6.0
PTT, Activated None 143 sec.
Alcohol None 350 mg/dl
Bilirubin (newborn) None 15 mg/dl
Calcium, ionized 0.77 mmol/L 1.59 mmol/L
Calcium, serum 6 mg/dl 13 mg/dl
BUN, serum None 80 mg/dl**
Creatinine, serum None 5.0 mg/dl**
Glucose, serum 50 mg/dl 450 mg/dl
Magnesium, serum 1.0 mg/dl 4.0 mg/dl
Potassium, serum 2.8 mEq/L 6.0 mEq/L
7.0 mEq/L (NICU)
Sodium, serum 125 mEq/L 160 mEq/L
Troponin I None 0.4*** ng/mL
Total C02, serum 10 mEq/L 40 mEq/L
pCO2, arterial or capillary 20 mmHg 70mmHg
PH, arterial or capillary 7.25 7.60
p02, arterial or capillary 40 mmHg None
Positive initial malaria identification    
Positive culture: blood, CSF, body fluid, tissue    
Positive Gram stain: CSF, body fluid, tissue    
Positive CSF finding (other): Cryptococcal antigen    

*Unless a known chronic leukemia patient
**Unless a known patient with renal failure
***Unless a known patient with high troponin

Critical Values for Therapeutic Drug Levels

Drug Therapeutic Level Toxic Levels
(Call Results)

Antibiotics

Gentamicin Peak: 4.0-10.0 mcg/mL
Trough: 0.0-2.0 mcg/mL
Single day dosing:
0.0-1.0 mcg/mL
Peak:>10.0 mcg/mL
Trough: >2.0 mcg/mL
Single day dosing:
>1.0 mcg/mL
Tobramycin Same as above Same as above
Vancomycin Peak: 30.0-40.0 mcg/mL
Trough: 5.0-10.0 mcg/mL
Peak: >40.0 mcg/mL
Trough:>12.0 mcg/mL

Anticonvulsants

Carbamazepine
(Tegretol)
8.0-12.0 mcg/mL (single agent)
6.0-10.0 mcg/mL(multiple drugs)
>15.0 mcg/mL
>12.0 mcg/mL
Phenobarbital 15.0-40.0 mcg/mL >50.0 mcg/mL
Phenytoin
(Dilantin)
10.0-20.0 mcg/mL >25.0 mcg/mL
Valproic Acid 50.0-100.0 mcg/mL >125.0 mcg/mL

Bronchodilators

Caffeine 10.0-20.0 mcg/mL >20.0 mcg/mL
Theophylline 5.0-15.0 mcg/mL (adult)
10.0-20.0 mcg/mL (0-19 years)
>20.0 mcg/mL
>20.0 mcg/mL

Cardiovascular

Digoxin 0.5-2.0 ng/mL >2.4 ng/mL
Procainamide 4.0-10.0 mcg/mL >10.0 mcg/mL
PA + NAPA levels in renal insufficiency PA + NAPA: 5.0-30.0 mcg/mL >30.0 mcg/mL
Quinidine 1.5-5.0 mcg/mL >5.0 mcg/mL

Other Agents

Acetaminophen 10-30 mcg/ml >120 mcg/ml
Cyclosporine 100-300 ng/ml >300 ng/ml
Lithium 0.5-1.0 mEq/L >1.1 mEq/L
Salicylate <20 mg/dl >30 mg/dl

Critical Values for Microbiology Testing

Finding Call to Physician or Designee Call to Nursing Unit or Physician Office Call to Infection Control Practitioner
Positive blood culture

Xa

Xb

 

Significant CSF findings:

  1. Positive direct exam
  2. Positive culture
  3. Positive Cryptococcal antigen
X   If gram-negative diplococci are observed on Gram stain or if N. meningitidis is recovered by culture.
Positive Gram stain or culture of:
  1. Internal organ tissue
  2. Sterile body fluids
X    
AFB findings:
  1. Positive smear.
  2. Positive AFB culture (if original smear is negative).
  3. Identification of Mycobacterium tuberculosis.
X

Xc

X
Positive malaria smear

X

   
a Results are called to physician 0700 - 2200. After 2200, nursing unit is called and the physician is notified the following morning.
b BMH and PMH only.
c Only if patient is still an inpatient.

Other Noncritical Microbiology Reports Called

Finding Call to Physician or Designee Call to Nursing Unit or Physician Office Call to Infection Control Practitioner
Positive catheter tip (>15 CFU)   X  
Respiratory tract specimen positive for N. meningitidis  

X

X
Identification of vancomycin resistant Enterococci    

Xa

Genital specimens—positive for group B Strep X    
Throat specimen—positive culture or antigen test for group A Strep X    
Positive culture for N. gonorrhoeae X    
Positive amplified test for N. gonorrhoeae DNA

X

   
Positive amplified test for Chlamydia trachomatis DNA

X

   
Positive culture for enteric pathogen X    
Positive O+P exam X    
Positive test for Clostridium difficile toxins A/B  

Xb

 
a Inpatient only
b PMH and BMH only

Critical Values for Blood Banking

Critical Result Patient's Physician Notified by Medical Director Patient Care Unit Notified by Blood Bank Technologist Verification and Read Back Blood Bank Medical Director or Pathologist on Call
Acute hemolytic transfusion reaction

X

X

X

X

Detection of bacterial contamination of blood product

X

X

X

X

Positive DAT—specific antibody identified in eluate  

X

X

X

Antigen negative red cells not available on site for inpatient transfusion  

X

X