Clinical Hemorheology and Microcirculation 37 (2007) 309–318 309 IOS Press Fibrinogen, plasma viscosity and blood viscosity in obesity. Relationship with insulin resistance E. Solá a , A. Vayá b,∗ , M. Simó b , A. Hernández-Mijares a , C. Morillas a , F. España c , A. Estellés c and D. Corella d a Endocrinology Service, Doctor Peset University Hospital, Valencia, Spain b Hemorheology and Thrombosis Unit, Department of Clinical Pathology, La Fe University Hospital, Valencia, Spain c Research Centre, LaFe University Hospital, Valencia, Spain d Department of Preventive Medicine, School of Medicine, University of Valencia, Valencia, Spain Received 5 January 2006 Accepted 31 January 2007 Abstract. Plasma viscosity (PV) and blood viscosity (BV) have been scarcely evaluated in morbid obese patients with no other concomitant cardiovascular risk factors. Contradictory results have been published regarding the influence of insulin resistance on these rheological parameters in obesity. In 67 severe or morbid obese patients without other cardiovascular risk factors (51 women and 11 men, aged 34 ± 11 years), fibrinogen, PV and BV at native (nBV) and corrected 45% hematocrit (cBV) have been determined, and insulin resistance has been calculated with homeostasis model assessment (HOMA) index, in basal conditions and after a three month diet period. The same determinations were performed in 67 healthy volunteers (45 women, 22 men, aged 32 ± 10 years) at baseline and three months later. When cases and controls were compared, obese patients showed higher fibrinogen levels (P< 0.001), PV (P = 0.050) and cBV (P = 0.035), and showed a higher insulin resistance than the control group (P< 0.001). Differences in PV were maintained after adjusting for BMI (P = 0.001), but disappeared after adjusting for HOMA (P = 0.391) fibrinogen (P = 0.367) and LDL-chol (P = 0.097). Differences between obese patients and the control group for cBV disappeared after adjusting for BMI (P = 0.739), HOMA (P = 0.744), fibrinogen (P = 0.907), LDL-chol (P = 0.283) and PV (P = 0.112). The achieved weight loss (8.7 ± 3.53%) was not accompanied by any changes in these rheological parameters (P> 0.050). Obese patients show increased fibrinogen levels, PV and cBV. These rheological disturbances seem to be associated with insulin resistance and the metabolic syndrome, and do not seem to improve with moderate weight loss. Keywords: Plasma viscosity, blood viscosity, obesity, hemorheology 1. Introduction Obesity is a highly prevalent disease which is associated with several cardiovascular risk factors, such as diabetes mellitus, arterial hypertension and dyslipidemia. As these cardiovascular risk factors are associated with rheological disturbances [1], the role of obesity “per se” in the hemorheological * Corresponding author. E-mail: vaya_amp@gva.es. 1386-0291/07/$17.00  2007 – IOS Press and the authors. All rights reserved