Eur J Haematol. 2021;106:597–605. | 597 wileyonlinelibrary.com/journal/ejh 1 | INTRODUCTION Much evidence suggests that blood viscosity (BV) is involved in some pathological processes, such as myocardial ischemia, strokes, and cognitive deficits. In addition, there are data pointing to the higher BV in individuals with sleep apnea, hyperlipidemia and hyperpro- teinemia, with arterial hypertension, and in dehydrated individuals. 1 Some of the known risk factors that alter BV in pathophysiological processes are diabetes, smoking, aging, and obesity. 2 Blood viscosity is a general measure of intrinsic resistance to blood flow and is determined mainly by hematocrit, plasma viscosity, and the deformation and the aggregation of erythrocytes. Moreover, BV varies with shear rate such as non-Newtonian fluid. Therefore, it is an important property for the regulation of blood rheological con- ditions (for producing resistance to fluid deformations) to determine blood flow and to determine tissue perfusion. 1,3 Because it is an in- trinsic property of blood flow and tissue perfusion, changes in BV and its rheological parameters can promote micro- and macrovas- cular damage and, as a consequence, major cardiovascular events. 2 The blood represents about 7% of an individual's body weight and consists of plasma (a liquid part of the blood that contains var- ious substances), red blood cells (RBCs), leukocytes (white blood cells), and platelets (cell fragments). Its essential function is the transport of substances, such as hydrogen, oxygen, electrolytes, and nutritional substances, in addition to products of cellular me- tabolism. RBCs pass through capillaries in the circulatory system and are exposed to various shear stresses in the blood flow. One of the unique features is the ability to change shape in response to external forces. This important phenomenon defines its mechanical behav- ior and function, since it is known that the reduced deformability Received: 23 November 2020 | Revised: 26 January 2021 | Accepted: 27 January 2021 DOI: 10.1111/ejh.13594 REVIEW ARTICLE Standardization for obtaining blood viscosity: A systematic review Marcel Valério de Arruda 1 | Alana Cruz Silva 1 | José Carlos Fernandes Galduróz 2 | Ruth Ferreira Galduróz 1 © 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd 1 Programa de Pós Graduação em Neurociência e Cognição, Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, Santo Andre, Brazil 2 Departamento de Psicobiologia, Universidade Federal de São Paulo, São Paulo, Brazil Correspondence Marcel Valério de Arruda and Ruth Ferreira Galduróz, Universidade Federal do ABC, Centro de Matemática, Computação e Cognição, Avenida dos Estados, 5001 – Bangú, Santo André, SP, 09210-580, Brazil. Email: marcel.a@aluno.ufabc.edu.br Funding information I would like to thank the Federal University of ABC for their help in offering me the resources in running the project, and the CNPq (National Council for Scientific and Technological Development) for providing the scientific initiation funding and for keeping science funded. Abstract Introduction: There is evidence to suggest that blood viscosity (BV) is involved in several pathological processes. In this review, we evaluated the different methods of BV acquisition, analyzing the sample storage time, the storage temperature, the ac- quisition time, the acquisition temperature, sample volume, and shear rates, in order to standardize this technique. Methods: We selected 50 articles with methods of obtaining BV, evaluating patholo- gies through BV, comparing rheological equipment, monitoring, and regulating BV. Results and conclusion: Measurements should be obtained as soon as possible, to reduce hemorheological changes. It is necessary to refrigerate them at 4°C when the storage time is long. The acquisition time is related to the equipment used. BV measurements at 37°C will represent the real BV in vivo more faithfully. In order to understand the BV phenomena, the shear rates must be between 0.1 and 1000 s-1. There is a wide variety of equipment available for measuring the BV. KEYWORDS blood, hemorheology, measurement protocol, reproducibility, viscosity