Table 1 Results of duplicate sample tests in testing and external quality control laboratories
From: Viral load testing in a resource-limited setting: quality control is critical
Lab 1 vs. Lab 2 2006 | Lab 1 vs. Lab 3 2006 | Lab 2 vs. Lab 4 vs. Lab 5* 2007 | |
|---|---|---|---|
Number of sample sets | 21 | 29 | 10 |
Range of log VL results reported | ND-6.1 | ND-5.7 | ND-4.6 |
N (%) of duplicate samples with difference in log VL result >1.0 | 13 (62%) | 14 (48%) | 1 (10%) |
Mean (range) absolute difference in log VL result | 1.1 (0.0-2.8) | 1.2 (0.0-3.1) | 0.2 (0.0-1.2) |
Limits of agreement of tests (log VL result)† | -4.777 to 0.801 | -3.089 to 3.246 | -0.796 to 0.848 |
False negatives: N (%) VL undetectable in testing lab but >1000 copies/mL in QC laboratory [same comparison but >5000 copies/mL] | 0 | 5 (17%) [5 (17%)] | 0 |
False positives: N (%) >1000 copies/mL in testing lab but undetectable in QC laboratory [same comparison but >5000 copies/mL] | 6 (29%) [1 (5%)] | 8 (28%) [5 (17%)] | 0 |