Monitoring human cytomegalovirus viral load in peripheral blood leukocytesof renal transplant recipients by a simple limiting dilution-PCR assay

To assess the clinical relevance of a semi-quantitative measurement of huma n cytomegalovirus (HCMV) DNA in renal transplant recipients within the typi cal clinical context of a developing country where virtually 100% of both r eceptors and donors are seropositive for this virus, we have undertaken HCM V DNA quantification using a simple, semi-quantitative, limiting dilution p olymerase chain reaction (PCR). We evaluated this assay prospectively in 52 renal transplant patients from whom a total of 495 serial blood samples we re collected. The samples scored HCMV positive by qualitative PCR had the l evels of HCMV DNA determined by end-point dilution-PCR. All patients were H CMV DNA positive during the monitoring period and a diagnosis of symptomati c infection was made for 4 of 52 patients. In symptomatic patients the geom etric mean of the highest level of HCMV DNAemia was 152,000 copies per 10(6 ) leukocytes, while for the asymptomatic group this value was 12,050. Sympt omatic patients showed high, protracted HCMV DNA levels, whereas asymptomat ic patients demonstrated intermittent low or moderate levels. Using a cut-o ff value of 100,000 copies per 106 leukocytes, the limiting dilution assay had sensitivity of 100%, specificity of 92%, a positive predictive value of 43% and a negative predictive value of 100% for HCMV disease. In this pati ent group, there was universal HCMV infection but relatively infrequent sym ptomatic HCMV disease. The two patient groups were readily distinguished by monitoring with the limiting dilution assay, an extremely simple technolog y immediately applicable in any clinical laboratory with PCR capability.