TABLE 6.

Estimating limits for controlsa

Time pointAvg CT valueSD
Initial38.062.15
Month 138.162.60
Month 237.620.75
Month 337.751.03
Avg37.901.60
  • a One approach for establishing the target value and limits for controls involves determining an initial temporary target value by assaying the control material a minimum of 20 times. The temporary value is used for the next 3 to 6 months (or for x number of runs, e.g., 20 to 30), during which time testing is presumed to be stable. The final target value and standard deviation are determined from the consecutive monthly values. The data presented are for a low-positive control in a real-time PCR assay to detect herpes simplex virus type 1 (HSV-1). The CT value refers to the number of cycles required for the fluorescence signal to cross threshold. The final target value (CT) ± SD is 37.90 ± 1.60.