Anemia is a widespread health issue impacting more than 2 billion people worldwide. In sickle cell disease (SCD), which impacts more than 100k individuals in the USA, severity of anemia is associated with complications, end organ damage, and poor quality of life. The gold standard test for hemoglobin (Hgb) monitoring is the complete blood count, which is invasive and costly. Therefore, we developed and launched a smartphone app that measures Hgb levels using fingernail pictures. We further refined this app to investigate effectiveness and usability in adults with SCD particularly in the context of vaso-occlusive crisis. This app is noninvasive, patient-supported, easy to use, and accessible, having been downloaded more than 250,000 times across the USA with thousands of active users per month and more than 1.6 million tests taken since launch in Dec 2021. While this technology has been evaluated in adult populations with SCD, pediatric populations present additional challenges. Very low hemoglobin (anemia) is one of the major complications in childhood SCD as a result of acute splenic sequestration, acute marrow aplasia (Parvo B19) or hemolysis and may necessitate emergency intervention including blood transfusions. These factors, combined with the stress and anxiety of blood draws, highlight the need for noninvasive, frequent monitoring in pediatric populations. This investigational app has not been reviewed or approved for SCD by the FDA.

In this study, which is ongoing, we enrolled 30 participants (15 Female/15 Male, average age: 11 years old ±5 years, ages 6 months to 5 years: 5, ages 6 years to 11 years: 13, ages 12 years to 17 years: 12) diagnosed with SCD (17 Hgb SS, 11 Hgb SC, 2 Hgb Sb+ thalassemia) in 2 cities (Atlanta, and Washington D.C). No participants met the exclusion criteria of presence of nailbed discoloration or limited technological competence regarding smartphone use. The study consisted of up to 3 site visits across a total of 12 weeks. At each visit, participants took an app test and received a venous Hgb blood test, the first of which was used to calibrate the app which was then recalibrated at subsequent visits. In between visits, participants took app tests every other day and recorded their symptoms and medications in the app.

In this study, we found the mean absolute error (MAE) of the test to be ±0.57 g/dL (R= 0.96, root mean squared error = ± 0.7 g/dL, 95% limits of agreement = ±1.3 g/dL), which is within the range of accuracy accepted by the FDA and similar to what we reported in adult populations with SCD. Furthermore, accuracy was consistent across age groups, indicating that the user (patient vs. Caregiver) as well as user skill (technological experience and ability to focus on tasks increases with age) had little impact on app results. Despite the variability introduced by a significantly anemic population and self-testing in a variety of locations and background lighting conditions, these results are similar to our previously published results obtained in clinical settings (Mannino et. al., Nature Communications, 2018, Mannino et. al. PNAS, 2025).

Study participants and their caregivers were eager to use the app, with each participant taking an average of 26 tests in the first 4 weeks of the study, with an 85% compliance (defined as the percentage of 2-day windows in which a participant records an app use. This represents a slightly increased compliance compared with our adult study, indicating the desire of children and their caregivers to use noninvasive tools to help assess their health. Furthermore, the noninvasive nature of this tool is cited by participants as a major positive attribute, as many children are apprehensive about more invasive procedures.

The ability of the app to accurately measure Hgb levels in children as well as robust at-home compliance highlights the utility of this tool as an accessible noninvasive screening platform. Furthermore, these results highlight the need for future research to better understand the relation of reported symptoms, including vaso-occlusive pain events and Hgb, particularly in the presence of hydroxyurea, of which 14 of our participants took regularly, which was an increase from our adult study cohort. Overall, the degree of accuracy reported suggests that this noninvasive app is a useful tool for children suffering from SCD to frequently monitor their Hgb levels, empowering them to better self-manage their condition.

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2025
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