Background and Objective: Sodium is the major cation of the extracellular fluid and has a potent influence on fluid movement.Sodium has been likened to a sponge that draws fluids into the extracellular space,including the plasma volume,to equalize gradients in concentration.There are some extreme occupational or exercise-related conditions where sweat losses are great and Na+ losses may exceed normal dietary intake.This can occur acutely such as in an ultra-endurance event or chronically as in hard manual work in the hear.In such cases,its wearable biometric diagnosis by using sensors such as bracelets,watches,skin patches,headbands,earphones,and clothing should be designed and developed.The optical/photonic sensors are a kind of ideal candidate of wearable biometric sensors.As a primary investigation,the effects of dilution on blood coagulation with normal or hypertonic saline were studied using the optical coherence tomography technique in this paper.Study Design/Materials and Methods: In this study,we investigated the effects of dilution with hypertonic(7.5%)and normal(0.9%)saline on the optical properties of blood during coagulation in vitro using optical coherence tomography.The optical coherence tomography signal slope,1/e light penetration depth,and attenuation coefficient were obtained from the profiles of reflectance versus depth.The normal whole blood served as the control group.Results:After 1 h coagulation,the average optical coherence tomography signal slope totally decreased by 22.9%,22.7%,and 17.8%when 0.9%normal saline solution replaces 2%,11%,and 20%of blood volume,respectively.The total decreases were 23.7%,29.8%,and 33.6%,respectively,with 2%,11%,and 20%blood volume replacement by 7.5%hypertonic saline.The total decrease of the control group was 23%.The average coagulation time were(420 ± 16),(418 ± 16),and(358 ± 14)s,respectively,with blood volume replacement of 2%,11%,and 20%by 0.9%normal saline.At 2%,11%,and 20%blood volume replacement with 7.5%hypertonic saline,the average coagulation time were(422 ± 17),(1160 ± 45),and(1730 ± 69)s,respectively.For normal whole blood,the average coagulation time was(425 ± 19)s.Obtained results indicated that the dilution with normal saline has a procoagulant effect when it replaces 20%of blood volume,and hypertonic saline has an anticoagulant effect if it replaces 11%or more of blood volume.Conclusions: Optical coherence tomography may be a potential technique to quantify and follow the liquid-gel transition during the coagulation process of blood diluted by normal and hypertonic saline.