Q fever laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Ahmed Younes M.B.B.CH [2]

Overview

Laboratory findings consistent with the diagnosis of Q fever include positive serology for antibodies (especially indirect immunofluorescence (IIF), positive PCR, and elevated liver enzymes.

Laboratory tests

Serologic testing for Q fever

• Indirect immunofluorescence (IIF) is the method of choice for antibody detection and is preferred over ELISA and complement fixation.
• Antibodies start to be detected after 7-14 days of infection, with most patients testing positive by the third week.
• Anti phase II antibodies are tested first. If positive, anti phase I antibodies are tested.
• After acute infection, serologic follow-up for serum anti phase I IgG antibodies. The test is done twice every 3 months for 2 years. If it's positive, a transesophageal echo should be done to rule out endocarditis.
• All serologic test results should be used in the context of clinical data because false positive test results are seen in many other diseases (e.g. leptospirosis).

Polymerase chain reaction (PCR)

• PCR can be used to detect C. burnetii DNA in cultures and clinical samples.
• PCR is positive in the first week of infection, thus it can be used to diagnose Q fever in patients who are serologically negative in the early stages of the disease.
• Quantitative PCR also can be used in patients whose anti phase II IgG antibodies are persistently positive in order to detect chronic Q fever.

Cultures

• C. burnetii doesn’t grow on ordinary blood cultures but can be cultivated on special media as embryonated eggs or cell culture.
• C. burnetii is extremely infectious and samples should be handled with caution.

Liver function tests

• A two-to-three fold increase in AST and ALT is seen in most patients.