Agreement Between Dried Blood Spot and Plasma PCR in Infants With Congenital Cytomegalovirus Infection

Congenital cytomegalovirus (cCMV) infection is diagnosed by positive urine or saliva testing within 21 days after birth. Beyond this age, newborn dried blood spot (DBS) PCR can retrospectively diagnose cCMV infection but has lower sensitivity than urine or saliva PCR testing. The DBS PCR may be negative due to the absence of blood DNAemia at birth or to the technical limit of detection for DBS PCR. The objective of this study was to distinguish these two possibilities by determining agreement between DBS and plasma CMV PCR tests among cCMV-infected infants. This single center retrospective cohort study evaluated 70 cCMV-infected infants diagnosed by a positive urine CMV PCR, who had a CMV DBS at birth and a plasma PCR test within 31 days after birth. Clinical characteristics and viral loads were compared between groups according to paired DBS and plasma PCR results. Test agreement was calculated using Cohen's kappa coefficient. The DBS PCR sensitivity was 71% compared to urine PCR. Of the 70 subjects, 49 (70%) subjects were DBS+ /plasma+ , 1 (1.4%) were DBS+ /plasma-, 14 (20%) were DBS-/plasma+ , and 6 (9%) were DBS-/plasma-. Agreement between the tests was fair (κ = 0.348, 95% CI 0.115-0.581). Of the 20 subjects with DBS- tests, 6 (30%) had undetectable plasma DNAemia. Of the infants with DBS-/plasma+ PCR, plasma viral loads were significantly lower than infants with DBS+ /plasma+ PCR testing. Nearly a third of cCMV infected infants may be missed by DBS testing due to both biological and technical limitations of this method.