Performance Characteristics of the Daktari CD4 System

Transcription

1 Daktari Diagnostics, Inc. 85 Bolton Street Cambridge, MA USA Performance Characteristics of the Daktari CD4 System 2 February 2015 Scope The Daktari CD4 system has been evaluated through studies of HIV- negative and HIV- positive subjects in Boston, USA; Nairobi, Kenya; and Kalisizo, Uganda. Accuracy Accuracy was evaluated by comparison to the BD FACSCalibur system as a reference method. Venous whole blood samples and fingerstick capillary blood samples were obtained from 141 HIV- positive adult individuals presenting for HIV care at health centers in Nairobi, Kenya. Fingerstick blood samples were analyzed using the Daktari CD4 system at the health care facility, immediately after sample collection. Venous blood samples were analyzed using the Daktari CD4 system and the BD FACSCalibur within 12 hours of sample collection. For calculation of Passing- Bablok regression, Pearson correlation, and Bland- Altman analysis, the first successful Daktari CD4 cell count measurement was used, and compared to the BD FACSCalibur cell count measurement. Results are illustrated graphically below. 1500" 1500$ Passing-Bablok&Regression& Passing4Bablok'Regression' 1250$ 1250" Slope&=&0.98&( )& 1000" Daktari'CD4' (cells/µl)' 750$ 750" 500$ 500" 250$ 250" 0$ 0" 0" 250" 500" 750" 1000" 1250" 1500" 0 $ $$$$250 $ $$$$$$$$$500 $$$$$$$$$$$$$$750 $$$$$$$$$$$$$$$$$$1000 $$$$$$$$$$$$1250 $ $$$$$1500$ FACSCalibur'CD4" (cells/µl)"

2 For 141 venous samples, the range of analyzed samples was 20 to 1441 cells/μl (Daktari CD4) and 10 to 1404 cells/μl (BD FACSCalibur). By Passing- Bablok regression, the slope (95% CI) was 0.98 (0.90 to 1.06) with an intercept (95% CI) of 30.4 ( to +5.2). The Pearson correlation coefficient (95% CI) between the two measurements was 0.90 (0.88 to 0.91). For 141 fingerstick samples, the slope (95% CI) was 0.97 (0.89 to 1.04) with an intercept (95% CI) of - 76 (- 109 to - 44). The Pearson correlation coefficient (95% CI) between the two measurements was 0.90 (0.89 to 0.91). Bias Bland- Altman analysis on 141 venous samples is shown in the figure below. The mean bias (95% CI bias) across all 282 samples was - 69 cells/μl (- 84 cells/μl to - 55 cells/μl). For venous samples only, the mean bias (95% CI bias) across 141 samples was - 41 cells/μl (- 61 cells/μl to - 21 cells/μl). For fingerstick samples only, the mean bias (95% CI bias) across 141 samples was - 98 cells/μl (- 118 cells/μl to - 78 cells/μl). Bland(and(Altman(plot( Difference((DDx(+(Venous(+(FACS)( 800$ 600$ 400$ 200$ 0$!200$!400$!600$!800$! 0$ 200$ 400$ 600$ 800$ 1200$ 1400$ 1600$ Average((FACS(+(DDx(+(Venous)/2( Bias$ CI$Bias$(95%)$ CI$(95%)$

3 Clinical Agreement Clinical agreement between Daktari CD4 and FACSCalibur, including sensitivity and specificity, was assessed by a two- by- two contingency table in two separate studies in Nairobi, Kenya. The results are illustrated in the tables and graphs below for the clinically relevant diagnostic cutoffs: 200 cells/μl, 350 cells/μl, and 500 cells/μl. In the first study, 20 consecutive patients presenting with CD4 counts in relevant ranges (<200, , , and >500 cells/μl) were enrolled, to assess performance across the entire clinical range. Only 14 patients were available with CD4 counts <200 cells/μl; as a result, a total of 74 subjects were evaluated. The data for venous samples are displayed graphically below. ART$Threshold Sensitivity$(95%$CI) Specificity$(95%$CI) PPV NPV LR0 LR+ CD4$<$ % ( 100.0% & 100.0% ) 77% ( 67.5% & 86.6% ) 50% 100% CD4$<$ % ( 100.0% & 100.0% ) 88% ( 80.0% & 95.0% ) 88% 100% CD4$<$500 98% ( 95.2% & 100.0% ) 75% ( 65.2% & 84.8% ) 92% 94% Pearson's)r)= 0.90 ( 0.89 & 0.92 ) 1500" 1500$ 1250" 1250$ Slope&=&0.93&( )& Passing.Bablok&Regression& 1000" DDx#$#Venous# 750" 750$ 500" 500$ 250" 250$ 0" 0$ 00" $ $$$$ " $ $$$$$$$$$ " $$$$$$$$$$$$$$ " $$$$$$$$$$$$$$$$$$ " $$$$$$$$$$$$ " $ $$$$$1500$ 1500" FACS#

4 In the second study, 141 consecutive patients presenting for routine care at HIV treatment centers were enrolled. The data are displayed in the tables below. ART$Threshold Sensitivity$(95%$CI) Specificity$(95%$CI) PPV NPV LR0 LR+ CD4$<$200 88% ( 83.6% ' 91.4% ) 89% ( 85.5% ' 92.8% ) 43% 99% CD4$<$350 97% ( 95.6% ' 99.3% ) 86% ( 81.7% ' 89.9% ) 72% 99% CD4$<$500 95% ( 92.1% ' 97.3% ) 70% ( 64.7% ' 75.3% ) 79% 92% Pearson's)r)= 0.89 ( 0.87 ' 0.90 ) FACSCalibur <200 >200 < > $ 1250$ Slope&=&0.98&( )& Passing.Bablok&Regression& Daktari <350 >350 < > $ 500$ <500 >500 < > $ 0$ 0 $ $$$$250 $ $$$$$$$$$500 $$$$$$$$$$$$$$750 $$$$$$$$$$$$$$$$$$1000 $$$$$$$$$$$$1250 $ $$$$$1500$ Precision Precision analysis was conducted for both repeatability and reproducibility. Within- laboratory, single instrument precision studies were conducted using samples from Boston, USA. Between 13 and 20 replicate runs were conducted using a single instrument and a single sample. Results are shown in the table and graph below. Coefficients of variation (CVs) ranged from 4 to 12%.

5 Precision (Repeatability) Daktari) CD4)count) (cells/µl) Precision)(repea<bility) Daktari'CD4'count Instrument V054 V059 V067 Mean,(cells/μL) St.,Dev %,CV FACSCalibur'CD4'count V054 V059 V067 Instrument)Serial)Number Within- laboratory, multiple instrument precision studies were conducted using samples from Boston, USA. Thirteen replicate runs were conducted across multiple instruments and samples. Representative results are shown in the graph below. Overall CVs ranged from 9-15%. Precision (Reproducibility) Daktari' CD4'count' (cells/µl) Precision'(reproducibility) Daktari'CD4'count Mean%(cells/μL) St.%Dev %%CV FACSCalibur'CD4'count FACS CD4 count (cells/µl) Disclaimer 1. The CD4 test provides information on the health and status of a patient s immune system. Results should be interpreted based on clinical and laboratory data. The Daktari CD4 should not be used as a standalone test without context; where clinical decision- making based on all available data are unclear, expert guidance and additional laboratory tests should be obtained. 2. The Daktari CD4 test is intended for use with capillary whole blood, or venous whole blood, using EDTA as anti- coagulant. Other anti- coagulants have not been tested and should not be used. 3. Daktari CD4 counts should be obtained only by personnel trained on the use of the Daktari system. Results may differ between laboratories and between operators.