Abstract—As an important target of point-of-care diagnostics, hematocrit is closely related to the health condition of human beings. Here, we developed a paper microfluidic chip for quantitative hematocrit measurement. The paper microfluidic chips were pretreated by sodium chloride, which would cause the dehydration of red blood cells and affect their flow abilities in the porous nitrocellulose paper. Plasma flowed ahead of red blood cells and separated from whole blood sample. We used the area of plasma region as the index to refer to the hematocrit, and built a linear calibration curve of plasma area versus hematocrit with R 2 > 0.92 for blood samples with hematocrit ranging from 30% to 60%, which covers the clinically relevant hematocrit range. I. INTRODUCTION Blood is the most important body liquid which contains wealth of information related to health conditions of human body. Hematocrit is the volume ratio of red blood cells in whole blood samples, which is related to gender, age and health conditions. For healthy people, the normal reference value of hematocrit is 35.5%~44.9% for female adults, 38.3%~48.6% for male adults [1]. For people with different health conditions, hematocrit may increase or decrease. Usually, people with anemia have a lower hematocrit, and people with cardiovascular disease may have a higher hematocrit. Hematocrit has been used as an important index to check the nutrition condition of patients, and hematocrit measurement is often used to screen patients for some specific diseases. There are already mature methods in hospitals and central laboratories for quantitative measurement of hematocrit such as centrifuge or automated hematology analyzer [2]. Although these quantitative measurements of hematocrit are accurate, the operation of equipment is complicated and time-consuming. In addition, the insufficient centrifugation caused by inexperienced operation can result in spuriously higher results [2,3]. By monitoring the non‑Newtonian flow of blood samples in a sub-millimeter tube, the doppler ultrasonic system has been used to estimate the hematocrit [4]. Near-infrared spectroscopy can be used to measure the hematocrit using dried blood spots [5,6]. While these nondestructive methods are able to rapidly report the real-time hematocrit level, they Zhiqing Xiao is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. Zitao Feng is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. Yuqian Yang is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. Zejingqiu Chen is with Department of Biology, Shantou University, 243 Daxue Road, 515063 Shantou, China. are unsuitable for point-of-care testing purpose. Thus, some portable tools developed for hematocrit measurement are increasingly interesting to point-of-care uses [7-9]. However, a simpler and cheaper method/tool is needed for resource-limited regions. As an emerging technology, microfluidics offers a great opportunity to build devices for such applications using a low volume of blood sample. Berry et al. built a multi-layer paper microfluidic device to measure hematocrit quantitatively, which utilized the pumping distance of red blood cells as the index [7]. However, this device required multi-layer lamination, and the test took ~30 min during which period the red blood cells may agglutinate together and stop flowing. Several other microfluidic chips have also been developed for quantitatively measurement of hematocrit, but complex optical [10-13] or electrical [14-17] setup needs to be integrated, which increases the cost on chip fabrication drastically. Considering the original definition of hematocrit, there are other measurement methods by separating the plasma portion and red blood cells portion. Previous research reports that salt can functionalize the microfluidic paper and result in the agglutination of red blood cells thereafter [18]. The osmotic pressure generated by the sodium chloride solution dehydrated red blood cells. The crenated red blood cells aggregated and lumped so that they were unable to enter the pores in the nitrocellulose medium. In this study, we propose a paper microfluidic chip that can be used for quantitative measurement of hematocrit and does not need complex fabrication or multiple assembly steps, with a high potential for large-scale manufacturing. This paper microfluidic chip is pretreated by sodium chloride, which has been proved to be able to cause dehydration of red blood cells and achieve plasma separation on capillary microfluidic platforms [19]. Blood samples with different hematocrit will have separated plasma of different volumes, which will result in different plasma areas. We can use the plasma area as the index to refer to hematocrit and build the relation between them, with the purpose for measuring hematocrit quantitatively. Lexin Sun is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. Rongkai Xu is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. Ruoqi Zeng is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. Weijin Guo is with Department of Biomedical Engineering, Shantou University, 243 Daxue Road, 515063 Shantou, China. *Corresponding Author: Weijin Guo. Email: guoweijin@stu.edu.cn Quantitative Hematocrit Measurement on a Paper Microfluidic Chip Pretreated by Sodium Chloride Zhiqing Xiao, Zitao Feng, Yuqian Yang, Zejingqiu Chen, Lexin Sun, Rongkai Xu, Ruoqi Zeng, Weijin Guo * 978-1-6654-8301-8/22/$31.00 ©2022 IEEE 59 Proceedings of the 17th IEEE International Conference on Nano/Micro Engineered and Molecular Systems April 14-17, 2022