Table 5.

Clinical utility of viral load in solid organ transplant recipients

General indication of use	Specific clinical utility	Commentsa
Prognostication	Assessment of CMV disease risk	Higher initial and peak viral loads are associated with a higher risk of CMV disease development (see the text); a rapid rise or upward trend in viral load is associated with a higher risk of CMV disease development (see the text)
	Assessment of CMV disease severity	Higher viral loads are associated with more severe CMV disease, tissue-invasive CMV disease, and potential multiorgan involvement (see the text)
Prevention	Guidance in the initiation and duration of preemptive therapy	Detection of a viral load above a predefined assay-specific threshold is an indication for the initiation of preemptive antiviral therapy; weekly NAT will guide in determining duration of preemptive therapy (see treatment below)
Diagnosis	Rapid and sensitive diagnosis of CMV infection	Rapid and sensitive detection of CMV in the blood or tissue of patients with compatible clinical symptoms confirms the clinical suspicion of CMV disease; higher viral loads are associated with more severe CMV disease, tissue-invasive CMV disease, and potential multiorgan involvement; a negative CMV NAT in blood does not completely rule out CMV disease if the clinical suspicion is high—in this case, pursue other diagnostic tests
Treatment	Assessment of efficacy of antiviral therapy	Weekly NAT will indicate the decline in viral load as a measure of the efficacy of antiviral therapy
	Assessment of treatment duration	Higher pretreatment viral loads (e.g., >18,200 [4.3 log10] IU/ml) have lower rates of CMV disease resolution; viral load suppression (e.g., <137 IU/ml or <2.1 log10 IU/ml) is associated with a shorter time to clinical CMV disease resolution
	Assessment of risk of relapse	Detection of a viral load above a threshold at the end of antiviral treatment is significantly associated with clinical and virological relapse; viral decay (t1/2) in patients with successful antiviral treatment was 3.17 days, compared to 8.8 days for patients with subsequent CMV relapse
	Assessment of risk of antiviral resistance	Persistent detection (or rise) of viral load in a patient receiving a prolonged course of antiviral therapy is a surrogate for the presence of a drug-resistant virus

^aThe viral load thresholds for most clinical indications have not been defined due to the lack of a standardized assay in most studies that have reported these clinical uses. See the text for examples of viral load thresholds specific to assays used and populations studied.