The RBC-diff accurately identifies red cell morphologies. (A) RBC-diff classification accuracy for a test set of 1334 manually labeled single-cell images. (B) Concordance of RBC-diff counts with expert quantitation on standard smear images (∼2000 RBCs per image) (mean algorithm-expert R²: 0.76; comparison with the individual experts shown in supplemental Figure 2; mean interexpert R², 0.75). (C) Mean difference in counts between pairs of smears created with different aliquots from the same blood sample compared with the expected difference when randomly sampled from a cell population twice (further details in Methods). (D) Association between RBC-diff cell density estimates on standard smear images and morphology grading flags at MGH (1+, 2+, 3+ reflect increasing frequency of the given morphology). See supplemental Figure 3 for the validation of this result at BWH. (E–I) Distributions associated with panels C and D are shown in supplemental Figures 10, 11, and 12. The distribution of the flags (panel D) is shown in supplemental Figure 3. All P values were calculated using a 2-sided Student t test. AUC, area under the receiver operating curve; N.f, not flagged.