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Hemoglobin level determines blood viscosity and as hemoglobin level rises, blood pressure rises. However, hemoglobin level in individuals is not fixed and change in hemoglobin is affected by various clinical conditions. The purpose of this study is to investigate whether the hemoglobin variability affects the development of hypertension using Korean cohort database. This study was conducted with 94,798 adults (age ≥ 40 years) who visited the health screening in 2006 or 2007 (index year) and had at least 3 health screenings from 2002 to 2007. Hemoglobin variability was assessed by 3 indices of coefficient of variation (CV), standard deviation, and variability independent of the mean. Cox proportional hazard regression analysis was performed for each index of quartile groups (Q1–Q4). A total of 29,145 participants (30.7%) had the incidence of hypertension during a median follow-up of 7.4 ± 2.5 years. In the multivariable adjusted model, the hazard ratio and 95% confidence interval for incidence of hypertension of Q2, Q3, and Q4 compared with Q1 of hemoglobin variability CV were 1.014 [0.981–1.047], 1.064 [1.030–1.099] and 1.094 [1.059–1.131] respectively. The results were consistent in various sensitivity and subgroup analyses. This study showed that hemoglobin variability could be associated with hypertension development. [ABSTRACT FROM AUTHOR]

• The erythrocyte cytoplasm is a colloid of hydrated hemoglobin molecules. • Hemoglobin hydration significantly affects the dielectric properties of whole blood. • A numerical method for analyzing impedance data is developed. • The hemoglobin molecule in the cytoplasm has primary and secondary hydration shells. • The primary and secondary shells' thicknesses are 0.39 and 0.20 nm, respectively. Electrochemical impedance spectroscopy of whole blood and blood cells has great potential for assessing the health of patients. This potential has not been fully exploited for a detailed examination of the erythrocyte interior. The erythrocyte interior (cytoplasm) is often considered as continuous media. However, cytoplasm is a colloidal suspension of hydrated hemoglobin molecules. This study mainly focuses on the effect of hemoglobin hydration on the dielectric properties of erythrocyte cytoplasm and whole blood. The impedance spectra of separated cytoplasm and whole blood were measured at frequencies from 1 kHz to 110 MHz. The effective medium theory was used to analyze the experimental data. The cytoplasm was found to be best described as a colloid of hemoglobin cores surrounded by double hydration shells. The dielectric properties of the hemoglobin core, hydration shells and free intracellular fluid, as well as the thickness of the shells, were numerically determined from the impedance spectrum. An approach was developed to determine the intracellular fluid's viscosity and the density of bound water in the hydration shells. It shows that the hemoglobin hydration has a significant effect on the physical properties of blood. The detailed electrical properties of the cytoplasm can be detected from the impedance spectrum of whole blood. [Display omitted] [ABSTRACT FROM AUTHOR]