Relapsing fever laboratory findings: Difference between revisions

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*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. <ref name="pmid26618151">{{cite journal |vauthors=Fotso Fotso A, Drancourt M |title=Laboratory Diagnosis of Tick-Borne African Relapsing Fevers: Latest Developments |journal=Front Public Health |volume=3 |issue= |pages=254 |date=2015 |pmid=26618151 |pmc=4641162 |doi=10.3389/fpubh.2015.00254 |url=}}</ref>
*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. <ref name="pmid26618151">{{cite journal |vauthors=Fotso Fotso A, Drancourt M |title=Laboratory Diagnosis of Tick-Borne African Relapsing Fevers: Latest Developments |journal=Front Public Health |volume=3 |issue= |pages=254 |date=2015 |pmid=26618151 |pmc=4641162 |doi=10.3389/fpubh.2015.00254 |url=}}</ref>


'''Blood culture'''
'''Blood culture''' and '''Serologic tests''' such as antibody tests and [[PCR]] are available through public health laboratories and some private laboratories. Although there are false-positive and false-negative results.


Blood samples obtained before [[antibiotic]] treatment can be cultured using BSK medium or by inoculating immature mice.  The spirochete will usually be evident within 24 hours if the blood was drawn during a febrile episode.
'''Serologic tests'''
Although not valuable for making an immediate diagnosis, serologic testing is available through public health laboratories and some private laboratories.  Acute serum should be taken within 7 days of symptom onset and convalescent serum should be taken at least 21 days after symptoms start.  Early [[antibiotic]] treatment may blunt the [[antibody]] response and the antibody levels may wane quickly during the months after exposure. To confirm the diagnosis of RF, Borrelia specific antibody titers should be increased between acute and convalescent serum samples and convalescent serum antibody levels should be at least two standard deviations above pooled negative controls. Patients with TBRF may have false-positive tests for Lyme disease because of the similarity of proteins between the two organisms.


'''Other laboratory findings include:
'''Other laboratory findings include:
'''
More common:
More common:
*Normal to increased white blood cell count with a left shift towards immature cells
*Normal to increased white blood cell count with a left shift towards immature cells

Revision as of 20:35, 9 August 2020

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

Laboratory Findings

Borrelia spirochetes
Peripheral blood smear from Schwan, Policastro et al 2003

Blood smear:

  • The presence of spirochetes in smears of peripheral blood, bone marrow, or cerebrospinal fluid in a symptomatic person 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. [1]

Blood culture and Serologic tests such as antibody tests and PCR are available through public health laboratories and some private laboratories. Although there are false-positive and false-negative results.


Other laboratory findings include: 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

References

  1. Fotso Fotso A, Drancourt M (2015). "Laboratory Diagnosis of Tick-Borne African Relapsing Fevers: Latest Developments". Front Public Health. 3: 254. doi:10.3389/fpubh.2015.00254. PMC 4641162. PMID 26618151.