TABLE 2.

Assay characteristics affecting variability of transplant viral load values

Assay characteristic	Example
Specimen type	Whole blood vs plasma
Kinetics of viral load	May vary by sample type, whole blood vs plasma
Form of the virus in the clinical specimen	Intact virus vs fragmented DNA
Extraction method	Efficiency of nucleic acid extraction with short fragments vs genomic DNA
Genetic target	Single gene, multicopy gene, degree of genetic variability
Amplicon size	CMV: assays with smaller amplicons (≤100 base pairs) provide higher viral load values than larger amplicons (>250 base pairs)