Differential sensitivity to hypoxia enables shape-based classification of sickle cell disease and trait blood samples

Differentiating between homozygous (disease) and heterozygous (trait) sickle cell patients is the key to ensuring appropriate long-term disease management. Well-equipped labs needed to perform confirmatory diagnostic tests are not available in endemic areas of most low- and medium-income countries. As a consequence of hemoglobin polymerization, red blood cells (RBCs) become sickle shaped and stiff under hypoxic conditions in sickle cell anemia patients. A simple test such as microscopy, using RBC shape as a biophysical marker, cannot conclusively differentiate between homozygous (disease) and heterozygous (trait) sickle blood. Here, we establish a new paradigm of microscopic diagnosis of sickle cell disease by exploiting differential polymerization of hemoglobin in disease and trait RBCs under controlled, chemically-induced hypoxia in a microfluidic chip. We use a portable smartphone microscope to compare the RBC shape distributions in blood treated with high and low concentrations of the hypoxia-inducing agent to correctly identify 35 blood samples as healthy, sickle cell disease or trait. Finally, we demonstrate our test in remote field locations to enable fast and confirmed diagnosis of sickle cell anemia in resource-limited areas. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial This was not a clinical trial. ### Funding Statement This project was supported by a Grand Challenges Explorations (phase 1) grant from Bill and Melinda Gates Foundation through their IKP-GCE program and a translation grant from Tata Centre for Technology and Design (TCTD), Indian Institute of Technology Bombay. R.M. and A.M. received salary support from a grant funded by the Wadhwani Research Centre for Bioengineering (WRCB), Indian Institute of Technology Bombay. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All studies using human blood samples were approved by the Institute Ethics Committee (IEC), IIT Bombay, with approval numbers IITB-IEC/2016/016, IITB-IEC/2017/020 and IITB-IEC/2018/042. Written informed consent to use leftover blood samples was taken from all participants. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Suitably de-identified images are available for research purposes from the corresponding author on request.