Important evidence for the link between blood viscosity and cardiovascular events was provided by the Edinburgh Artery Study in a random population of 1,592 men and women aged 55 to 74 years, who were followed over a mean period of 5 years. After adjustment for age and gender, mean values for both blood viscosity and hematocrit-adjusted blood viscosity were elevated in patients who experienced cardiovascular events (ischemic heart attacks and strokes) relative to those who did not. The differences in blood viscosity were statistically significant (p=0.0003), and the link between blood viscosity and the occurrence of cardiovascular events was at least as strong as that of diastolic blood pressure and LDL cholesterol and stronger than that of smoking. 
In a seminal report just prior to the publication of the Edinburgh Artery Study, Lousiana State University pathologist Gregory Sloop proposed that blood viscosity is the one unifying mechanism by which all established cardiovascular risk factors promote atherosclerosis, including LDL cholesterol, high blood pressure, diabetes, obesity and smoking . Numerous studies have confirmed the linkages between blood viscosity and the following cardiovascular risk factors:
- Hypertension [3-6]
- Hyperlipidema: positive correlation with LDL cholesterol, total cholesterol and triglycerides; negative correlation with HDL cholesterol [7-13]
- Diabetes, insulin resistance syndrome and obesity [12,14-18]
- Tobacco smoking [6,19-21]
- Male gender vs. premenopausal women [12-13,22-23]
- Aging [12,21,24]
In his report, which was titled A Unifying Theory of Atherogenesis, Dr. Sloop indicated that blood viscosity was uniquely suited to predict the entire course of cardiovascular disease because blood viscosity accomplishes the following: (i) accounts for the morphological similarity of atherosclerotic lesions associated with many diverse risk factors, (ii) explains the anatomic distribution of lesions throughout the body, (iii) provides a role for platelet activation by turbulent blood flow caused by hyperviscosity, (iv) includes an explanation of the protective role of HDL cholesterol (i.e., HDL has been shown experimentally to lower viscosity). 
Blood viscosity holds certain similarities with blood pressure. Like blood pressure, the viscosity of blood changes during each cardiac cycle and is reported using two numerical quantities: systolic and diastolic viscosity. However, while blood pressure is parameter of the circulatory system as a whole, blood viscosity is a parameter specific to the fluid flowing through the system. Therefore, viscosity can be said to precede pressure and to be biophysically more fundamental than pressure.
The Blood Viscosity Test is performed at Meridian Valley Lab using a calibrated glass capillary system that is classified as a Class I device under 21 CFR § 862.2920. The Blood Viscosity Test is not covered by insurance plans. Doctors must bill their patients or their patients’ caregivers for this service.
- Lowe GD, Lee AJ, Rumley A, et al. Blood viscosity and risk of cardiovascular events: the Edinburgh Artery Study. Br J Haematol 1997; 96:168-173.
- Sloop GD. A unifying theory of atherogenesis. Med Hypotheses. 1996; 47:321-5.
- Smith WC, Lowe GD, et al. Rheological determinants of blood pressure in a Scottish adult population. J Hypertens 1992; 10:467-72.
- Letcher RL, Chien S, et al. Direct relationship between blood pressure and blood viscosity in normal and hypertensive subjects. Role of fibrinogen and concentration. Am J Med 1981; 70:1195-1202.
- Devereux RB, Case DB, Alderman MH, et al. Possible role of increased blood viscosity in the hemodynamics of systemic hypertension. Am J Cardiol 2000; 85:1265-1268.
- Levenson J, Simon AC, Cambien FA, Beretti C. Cigarette smoking and hypertension. Factors independently associated with blood hyperviscosity and arterial rigidity. Arteriosclerosis 1987; 7:572-577.
- Sloop GD, Garber DW. The effects of low-density lipoprotein and high-density lipoprotein on blood viscosity correlate with their association with risk of atherosclerosis in humans. Clin Sci 1997; 92:473-479.
- Lowe GD. Blood viscosity, lipoproteins, and cardiovascular risk. Circulation 1992; 85:2329-2331.
- Rosenson RS, Shott S, Tangney CC. Hypertriglyceridemia is associated with an elevated blood viscosity: triglycerides and blood viscosity. Atherosclerosis 2002; 161:433-9.
- Stamos TD, Rosenson RS. Low high density lipoprotein levels are associated with an elevated blood viscosity. Atherosclerosis 1999; 146:161-5.
- Hoieggen A, Fossum E, Moan A, Enger E, Kjeldsen SE. Whole-blood viscosity and the insulin-resistance syndrome. J Hypertens 1998; 16:203-10.
- de Simone G, Devereux RB, Chien S, et al. Relation of blood viscosity to demographic and physiologic variables and to cardiovascular risk factors in apparently normal adults. Circulation 1990; 81:107-17.
- Rosenson RS, McCormick A, Uretz EF. Distribution of blood viscosity values and biochemical correlates in healthy adults. Clin Chem 1996; 42:1189-95.
- Tamariz LJ, Young JH, Pankow JS, et al. Blood viscosity and hematocrit as risk factors for type 2 diabetes mellitus: The Atherosclerosis Risk in Communities (ARIC) Study. Am J Epidemiol 2008; 168:1153-60.
- Jax TW, Peters AJ, Plehn G, Schoebel FC. Hemostatic risk factors in patients with coronary artery disease and type 2 diabetes – a two year follow-up of 243 patients. Cardiovasc Diabetol 2009; 8:48.
- Ernst E, Weihmayr T, et al. Cardiovascular risk factors and hemorheology. Physical fitness, stress and obesity. Atherosclerosis 1986; 59:263-9.
- Hoieggen A, Fossum E, et al. Whole-blood viscosity and the insulin-resistance syndrome. J Hypertens 1998; 16:203-10.
- Carroll S, Cooke CB, Butterly RJ. Plasma viscosity, fibrinogen and the metabolic syndrome: effect of obesity and cardiorespiratory fitness. Blood Coagul Fibrinolysis 2000; 11:71-8.
- Ernst E, Koenig W, Matrai A, et al. Blood rheology in healthy cigarette smokers. Results from the MONICA project, Augsburg. Arteriosclerosis 1988; 8:385-8.
- Ernst E. Haemorheological consequences of chronic cigarette smoking. J Cardiovasc Risk 1995; 2:435-9.
- Lowe GD, Drummond MM, Forbes CD, Barbenel JC. The effects of age and cigarette-smoking on blood and plasma viscosity in men. Scott Med J 1980; 25:13-7.
- Kameneva MV, Watach MJ, Borovetz HS. Gender difference in rheologic properties of blood and risk of cardiovascular diseases. Clin Hemorheol Microcirc 1999; 21:357-363.
- Fowkes FG, Pell JP, Donnan PT, et al. Sex differences in susceptibility to etiologic factors for peripheral atherosclerosis. Importance of plasma fibrinogen and blood viscosity. Arterioscler Thromb 1994; 14:862-8.
- Coppola L, Caserta F, De Lucia D, et al. Blood viscosity and aging. Arch Gerontol Geriatr 2000; 31:35-42.