Anthrax laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

Initial evaluation of patients suspected of having anthrax should be similar to the standard evaluation for patients with an acute febrile illness and should have an emphasis on obtaining pre-treatment blood and other appropriate cultures. When systemic anthrax is present, abnormalities in laboratory tests include anemia, thrombocytopenia, and leukocytosis particularly in the latter stages of the disease. Other laboratory findings are hyponatremia, increased BUN, elevated transaminase levels, hypoalbuminemia, and elevated troponin. Cell cultures from the initial skin lesion, blood, CSF, or pleural fluid can identify the organism and possibly the toxins. In injection anthrax, the typical laboratory finding is an inflammatory pattern with a low CRP. A normal PT/PTT at admission does not exclude coagulopathy nor DIC.

Laboratory Findings

Show below is a table depicting the tests are used in the diagnosis and monitoring of systemic anthrax.

Laboratory findings

Test	Initial Findings	Serial Monitoring
CBC	Hemoconcentration Possible thrombocytopenia Leukocyte count commonly normal	Anemia Thrombocytopenia Leukocytosis (late in disease)
Electrolyte Renal Panel	Decreased sodium level Increased BUN
Liver Enzymes Serum Albumin	Elevated transaminase levels Hypoalbuminemia
PT PTT D-dimer Fibrinogen	Normal PT/PTT does not exclude DIC or coagulopathy	Low threshold for hypercoagulability workup: Haptoglobin LDH Fibrin split products ADAMTS 13 if hemolytic anemia
C-Reactive Protein	Characterization of inflammatory response Typically low CRP in injection anthrax
Gram stain Cultures Toxic Assays (Blood, serum, CSF, pleural fluid, ascites, wound exudate*, bronchial exudate)	Cultures usually negative after antibiotics Toxins may be detected
Cardiac Enzymes BNP	Troponin leak caused by increased cardiac demand from infection (particularly if atrial fibrillation with rapid ventricular response)

* Note that topical swabs from skin lesions will not pick up B. anthracis. Detection in smears or by culture requires lifting the edge of the eschar with tweezers (this gives no pain unless there is secondary infection) and obtaining fluid from underneath. The fluid will probably be sterile if the patient has been treated with an antibiotic.