Tests
1st tests to order
white blood cell count with differential
Test
Order in all patients. Not specific for Chlamydia psittaci infection.
Result
slightly elevated with a left shift; eosinophilia later in disease course
liver function tests
Test
Order in all patients. Alanine transaminase (ALT) and aspartate transaminase (AST) can be slightly elevated. AST:ALT ratio <1 can suggest hepatitis. Sometimes total bilirubin is elevated and, along with elevated direct bilirubin, suggests cholestasis, which can be seen with systemic disease. Alkaline phosphatase is a more direct marker for cholestasis.
Result
normal or slightly elevated
polymerase chain reaction (PCR)
Test
Send a respiratory specimen for PCR, if available. Results are rapid and can be obtained in time to guide treatment decisions. PCR is more readily available than it was in the past, and real-time PCR assays are now available in some specialized laboratories. It is a highly sensitive and specific test for C psittaci. May also be performed on blood and tissue if necessary.[12]
Laboratories that perform these tests should be contacted early as careful specimen collection and handling are required.
Result
positive for Chlamydia psittaci
chest x-ray
Test
Order in all patients with suspected pneumonia. Reveals presence of pneumonia, but is not specific for C psittaci infection. Other findings include a diffuse ground-glass or miliary appearance, atelectasis in association with consolidation, hilar enlargement but never alone, and a reticular pattern.
Result
lobar consolidation with hilar enlargement; small pleural effusion
Tests to consider
serology
Test
Microimmunofluorescence (MIF) on paired serum samples (taken 2 to 4 weeks apart) is the preferred serologic test and can be performed as a supportive test when PCR is available, or as an initial test when PCR is not available. Tests are available in many laboratories. Consider collecting a third specimen 4 to 6 weeks after the acute specimen in patients started on antimicrobial therapy. Cross reaction between other Chlamydia species can occur; therefore, results should be interpreted with caution, especially if the titer is <1:128. MIF is more sensitive and specific compared with complement fixation tests.[12]
Result
positive for Chlamydia psittaci
culture
Test
Sputum, pleural fluid, conjunctival fluid, or clotted blood can be cultured. However, culturing C psittaci is not recommended unless an experienced reference laboratory is available. Testing can be hazardous to laboratory personnel and it is not as sensitive as PCR. Also, detection of the organism in tissue culture is not standardized.[1]
Result
positive for Chlamydia psittaci
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