PCR Assay of Dried Blood Fails to Detect Newborn CMV

Real-time polymerase chain reaction assays of dried blood spots are not sensitive enough to reliably identify cytomegalovirus infection in newborns.

Two such methods missed approximately two-thirds of the CMV infections in a prospective cohort study of 20,448 newborns, said Dr. Suresh B. Boppana of the University of Alabama at Birmingham and associates (JAMA 2010;303:1375–82).

"These results have major public health implications because they indicate that such methods, as currently performed, will not be suitable for the mass screening of newborns for congenital CMV infection—the most common nongenetic cause of deafness in the United States," they noted.

Traditional isolation of CMV from cultured saliva or urine samples is the standard method of identifying the congenital infection, but it is not amenable to mass screening. Experts had been hopeful that PCR technology would prove sensitive and specific at identifying occult CMV infection, since it is much better suited to mass screening "because it does not require tissue culture facilities and is amenable to automation with the screening of large numbers of specimens at low cost," Dr. Boppana and colleagues said.

Dried blood spots already are collected routinely for newborn metabolic screening, and there has been "considerable" enthusiasm for using PCR assays for CMV on such samples. But until now, the sensitivity and specificity of these techniques had not been determined, and their diagnostic accuracy has never been directly compared with that of standard tissue culture methods.

The researchers compared standard saliva culturing with dried blood spot sampling in infants born at seven U.S. medical centers in 2007–2008. Two different PCR techniques, a single-primer and a double-primer assay, were assessed.

A total of 92 infants (0.45%) were found to have congenital CMV infection.

Saliva screening correctly identified 91 of the 92 affected newborns (99%). In contrast, single-primer blood spot PCR identified only 17 of the 60 infants (28%) who were tested by that method and double-primer blood spot PCR detected only 11 of the 32 infants (34%) who were tested by that method.

The sensitivity and specificity of the single-primer blood spot PCR were 28% and 99.9%. The sensitivity and specificity of the double-primer blood spot PCR were 34% and 99.9%.

"Our data indicate that as many as 80% of infants with congenital CMV infections could be missed" with the dried blood spot real-time PCR assays, they said. It is likely that this failure was due to an absence of detectable CMV DNA in the peripheral blood of most newborns who have congenital CMV. These infants may have contracted the infection months before birth, and thus may no longer be viremic when tested.

This study was supported by the National Institute of Deafness and Other Communication Disorders. No financial conflicts of Interest were reported.