A method for determination of haematocrit using the mobile app 'HaemoCalc' : Validity, reliability, and effect of user expertise

We evaluated validity, reliability, and effect of user expertise of ‘HaemoCalc’, a mobile phone application for hematocrit (Hct) measurement from fingerpick blood samples, compared to a traditional Hawksley microhaematocrit reader (MHR). Experiment 1 examined the effect pitch angle during image capture exerted on the validity of Hct values. Twenty participants' samples were analysed at 0°, 10°, and 20° directly over the sample, and 33° with 10 cm setback. Analysis of variance (ANOVA) revealed a significant effect of angle on Hct values (P<0.01). Measurements at 33° pitch differed from other angles and the MHR (P<0.001, d=2.31–3.06). Bland-Altman analysis showed good agreement at 0°, 10°, and 20° (mean differences: –0.4% to 1.0%) but poor agreement at 33° (mean difference: -4.4%, LOA: -0.7% to 8.4%). Experiment 2 assessed inter- and intra-rater reliability of an expert and novice users (n=12). Participants performed three trials each. HaemoCalc and MHR showed excellent reliability (ICC=0.95–1.00). No differences were observed between an expert and novices (P=1.000, d=0.01-0.39). HaemoCalc is a valid and reliable tool for Hct measurement at small pitch angles and in expert and novice users. The HaemoCalc app offers scalability, repeatability, health and safety benefits, and potential applications in medical education and remote learning.