CMV pneumonitis laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Lab tests
- The detection of CMV in bronchoalveolar lavage (BAL) specimens in BMT (bone marrow transplantation) patients is highly predictive of CMV pneumonitis. In HIV infected patients the presence of CMV in BAL specimens is less predictive of CMV pneumonitis, and definitive diagnosis requires lung tissue specimens.
- CMV may be detected by culture, characteristic viral inclusions, or CMV antigens.
- Infected cells characteristically show large intranuclear inclusions with surrounding clearing, smaller cytoplasmic inclusions, and increased cell size
- Culture is not sensitive, at ~50%. A shell-vial technique is now commonly used and improves the speed (24-48 hours instead of weeks) and sensitivity of the test. It uses a fluorescence tagged monoclonal antibody to detect growth sooner than cytopathic changes develop.
- PCR (polymerase chain reaction) testing is not standardized but may become the best test; it’s sensitivity tends to be higher than other tests.
- Blood and urine should also be tested for viremia, but these are less sensitive than BAL.
- As suggested above, CMV may be seen in patients without evidence of active disease or inflammation, so CMV infection may not always be clinically significant.
- This is a particularly difficult scenario when evidence of CMV is found in BAL specimens performed for PCP. Studies have not shown that these patients overall were clinically any different or recovered any differently when treated for PCP than those patients treated with the same who did not have evidence of CMV.
- Cytopathic changes are probably more specific for significant disease than culture.
- CMV infection may be defined as seroconversion with the presence of IgM antibodies, a four-fold increase in anti-CMV IgG titers, or viral isolation by culture. In contrast CMV disease is defined as clinical evidence of CMV infection, including fever, leukopenia and/or end-organ involvement.
Electrolyte and Biomarker Studies
- LDH elevation in 94% – mean 450 IU/l
- pO2 reduced in most – severity is predictive of mortality
- Microangiopathic hemolytic anemia develops in some patients