Relapsing fever laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

• The presence of spirochetes in smears of peripheral blood, bone marrow, or cerebrospinal fluid in a symptomatic person is diagnostic of relapsing fever.

Laboratory Findings

Borrelia spirochetes

Peripheral blood smear from Schwan, Policastro et al 2003

Microscopic Diagnosis

• The presence of spirochetes in smears of peripheral blood, bone marrow, or cerebrospinal fluid which stained with Giemsa, May-Grünwald Giemsa, Wright, Wright-Giemsa, Field's, or Diff-Quick stains, or examined under dark-field while the patient is febrile, is diagnostic of relapsing fever. Although best visualized by darkfield microscopy, the organisms can also be detected by Wright-Giemsa or acridine orange-stained preparations.

• With subsequent febrile episodes, the number of circulating spirochetes decreases, making it harder to detect spirochetes on a peripheral blood smear. Even during the initial episode spirochetes will only be seen 70% of the time.

Molecular Diagnosis and serology

• Antibody tests and PCR is available through public health laboratories and some private laboratories. Although there are false-positive and false-negative results.

Other laboratory findings

More common:

• Normal to increased white blood cell count with a left shift towards immature cells
• Mild to moderate thrombocytopenia
• Mild anemia
• Elevated ESR

Less common:

• Mildly increased serum bilirubin and hepatic aminotransferase level
• increased urea nitrogen, creatinine
• Slightly prolonged coagulation tests, PT and APTT, as well as proteinuria or hematuria, are also common