52 B. D. HEDLEY ET AL. DXH 800 PERFORMANCE EVALUATION with PLT counts <20 · 109/l which showed disagree- ment, were ﬂagged for review by the analyzer. The number of all samples with ﬂagged PLT values was similar (10% on the DxH 800 and 9% on the LH 780) in this group of predominantly hematologically abnor- mal samples. NRBC A subset of samples were examined by manual review and FCM to determine the number of NRBCs in each (n = 246). Samples were in the range of 0 to 61 NRBCs/100 WBCs. The correct enumeration is clini- cally important as in the majority of situations it indi- cates stressed or disordered erythropoiesis and potential disease. A number of studies have repeatedly associated the presence of NRBCs with increased hos- pital mortality (Schwartz & Stansbury, 1954; Stachon et al., 2002; Kho et al., 2007). To determine the accu- racy of NRBC enumeration we evaluated the new DxH 800 compared to a FCM reference method that very accurately enumerates NRBCs. The correlation coefﬁcient between the DxH 800 and LH 780 was determined to be 0.819. However, comparison of the DxH 800 and LH 780 results to FCM (Figure 3a) showed a signiﬁcant improvement in correlation with the DxH 800 (r2 = 0.910) when compared to the pred- icate LH 780 analyzer (r2 = 0.791). A signiﬁcant dif- ference (P < 0.001, ANOVA) was found in the accuracy of the NRBC count between all three groups (DxH 800, LH 780, and FCM). Comparison of the DxH 800 vs. FCM counts showed no signiﬁcant difference (P > 0.05, Dunn’s post-test) whereas the LH 780 showed a signiﬁcant difference to the FCM counts (P < 0.05, Dunn’s post-test). This demonstrates improved NRBC enumeration by the DxH 800. ROC were generated for the DxH 800 vs. the reference FCM method. The AUC for the DxH 800 vs. FCM was determined to be 0.96 which shows a signiﬁcant improvement over the predicate analyzer (AUC = 0.76). Further ROC analysis determined that NRBC enumeration on the DxH 800 vs. FCM had excellent speciﬁcity of 100% and sensitivity of 73% (Figure 3b). The DxH 800 showed signiﬁcant improvements over the LH 780 in false negative (FN) rate, false posi- tive (FP) rate, sensitivity, speciﬁcity, and bias in the detection of NRBCs (shown in Table 5). Importantly, (a) (b) Figure 3. Nucleated red blood cell (NRBC) enumera- tion. (a) NRBC counts for all samples collected (n = 201) on the DxH 800 vs. ﬂow cytometry (FCM). r2 Value for DxH 800 vs. FCM was 0.910. (b) Recei- ver Operator Curves for DxH 800 vs. FCM. Sensitivity for DxH 800 vs. FCM was 73% and speciﬁcity for DxH 800 vs. FCM was 100%. there was a signiﬁcant decrease in false negative rate compared to the LH 780 (DxH 800, 6% vs. LH 780, 10%); furthermore, no false positives were detected on the DxH 800. The number of samples with the 2010 Blackwell Publishing Ltd, Int. Jnl. Lab. Hem. 2011, 33, 45–56