Investigations
1st investigations to order
no initial test
Test
Roseola can almost always be diagnosed based on the classic presentation of a previously healthy infant, 6 to 24 months of age, with a sudden onset of high fever for 3 to 7 days, followed by development of discrete red macules and papules on the trunk. For patients with this classic presentation, a clinical diagnosis can be made based on physical examination findings and history (usually at the time of loss of fever). Laboratory investigation is seldom necessary.[10]
Result
clinical diagnosis
Investigations to consider
viral culture
Test
Not often employed in clinical diagnosis, because, in isolation, it cannot accurately distinguish acute primary human herpesvirus (HHV)-6 infection from latent or persistent infection. Also, not commercially available.[16]
Viral culture is performed on isolated peripheral blood mononuclear cells with a high sensitivity and specificity.
Result
positive culture
antibody detection
Test
Seroconversion in paired serum specimens via enzyme immunoassay indicates recent infection.
Measuring IgM levels is not reliable in the diagnosis of HHV-6 or HHV-7 infection.
A significant increase in titre with enzyme immunoassay with a positive PCR result in a young infant is also highly suggestive of recent infection.
Indirect immunofluorescence and complement fixation immunofluorescence are infrequently used, and results depend on the skill of the interpreter.[2][18] IgG antibody avidity testing by immunofluorescence may also help to identify recent infection with HHV-6 or HHV-7. This test is rarely needed, though it may be useful in children with complicating medical factors (e.g., encephalitis) where diagnosis is uncertain.
Result
high HHV-6- or HHV-7-specific IgG levels
Emerging tests
polymerase chain reaction (PCR)
Test
Viral DNA amplification (PCR) may be useful in conjunction with a single negative serum serology specimen in detecting acute infection.[2] PCR viral panels, which may include HHV-6, are available at some institutions for testing cerebrospinal fluid in patients with encephalitis. Comparison of viral copy number over time can be helpful in diagnosis of reactivation in people who are immunosuppressed.
Result
may be positive for HHV-6
immunohistochemistry
Test
Cells with an active infection will stain positively when immunohistochemistry is performed on tissues with monoclonal antibodies to HHV-6.
This test is rarely needed, though it may be useful in children with complicating medical factors (e.g., encephalitis) where diagnosis is uncertain.
Result
positive
Use of this content is subject to our disclaimer