Viral load assay sensitivity and low level viremia in HAART treated HIV patients.
BACKGROUND
The recent introduction of highly sensitive viral load assays resulted in a significant increase in number of treated HIV-infected patients with a detectable viral load. The significance of a viral load between 20 and 50 copies/mL remains unclear.


OBJECTIVE
To compare the performance of three viral load assays, with special attention for specificity and sensitivity at the lowest level of quantification.


METHODS
Samples (n=181) were selected from 62 HIV-positive individuals that experience viral blips or episodes of low but detectable viremia under antiretroviral treatment, and from 216 HIV-negative individuals. Each sample was tested in at least two of three assays: the Cobas Amplicor HIV-1 Monitor (CAP/CA), the Cobas Ampliprep/Cobas TaqMan HIV-1 version 1 (CAP/CTM1) and the Cobas Ampliprep/Cobas TaqMan HIV-1 version 2 (CAP/CTM2).


RESULTS
No false positive results were recorded. Kappa statistics revealed fair to moderate agreement between the results of the three assays, but important differences in sensitivity were observed, with the highest sensitivity reported for CAP/CTM2 followed by CAP/CTM1 and CAP/CA. The differences in sensitivity remained after equalization of the detection limit for all assays at 50 copies/mL. Analysis of samples collected over time showed that patients with single blips in CAP/CA present with recurrent blips in CAP/CTM1 and persistent detectable viremia in CAP/CTM2.


CONCLUSIONS
Viral load results between 20 and 50 copies/mL in either CAP/CTM1 or CAP/CTM2, indicate true viremia. The availability of highly sensitive assays force reconsideration of the terms 'undetectable' viral load and 'virological success' of antiretroviral treatment.
Ghent University, AIDS Reference Laboratory, De Pintelaan 185, B-9000 Ghent, Belgium. chris.verhofstede@ugent.be
Chris
C
Verhofstede
Filip
F
Van Wanzeele
Jacqueline
J
Reynaerts
Marianne
M
Mangelschots
Jean
J
Plum
Katrien
K
Fransen
D019380:Anti-HIV Agents / Q000627:therapeutic use*; D023241:Antiretroviral Therapy, Highly Active; D002648:Child; D002675:Child, Preschool; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000821:virology*; D015497:HIV-1 / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D012680:Sensitivity and Specificity; D019562:Viral Load / Q000379:methods*; D014766:Viremia
D019380:Anti-HIV Agents