Subclinical Hypothyroidism and Cardiovascular Risk

Background: Subclinical hypothyroidism (SCH) has been suggested to be associated with increased cardiovascular risk by different mechanisms. Several cardiovascular risk factors have been analysed, but yielded controversial results.

Objectives: We aimed to analyse whether there are differences in several cardiovascular risk markers, such as lipids, inflammatory parameters: plasma viscosity (PV), fibrinogen and C reactive protein (CRP); homocysteine (Hcy) and red blood cell distribution width (RDW), when comparing SCH and controls. We also analysed which of these parameters predict SCH risk and constitute independent markers.

Methods: We determined PV in a Fresenius capillary plasma viscosimeter, Hcy by a chemiluminiscent enzyme immunoassay, and biochemical and haematological parameters by conventional laboratory methods in 58 SCH outpatients and 58 controls matched for age and gender.

Results: SCH patients did not show statistical differences for glucose, lipids or leucocytes (p > 0.05). However, patients showed a higher prevalence for use of hypolipidaemic drugs, body mass index (BMI), thyroid stimulating hormone (TSH), PV, CRP, fibrinogen, Hcy and RDW (p < 0.05). RDW correlated with inflammation parameters: PV (r = 0.331, p < 0.05), fibrinogen (r = 0.424, p < 0.05), CRP (r = 0.433, p < 0.01) and leucocytes (r = 0.613, p < 0.01). None of the cardiovascular markers correlated with the TSH levels (p > 0.05) In the unadjusted logistic regression analyses, BMI ≥28 kg/m2, RDW ≥14%, Hcy ≥12 μm/L, fibrinogen ≥400 mg/dL and MCV ≤88 fL increased SCH risk, but only RDW ≥14% and fibrinogen ≥400 mg/dL independently increased this risk in the adjusted logistic regression analyses (OR = 4.68, 95% CI 1.20-18.30 P = 0.026; OR = 3.48, 95% CI 1.08-11.23 P = 0.037).

Conclusion: SCH patients show a higher cardiovascular risk, characterised by increased PV, fibrinogen, Hcy and RDW. However, only fibrinogen ≥400 mg/dL and RDW ≥14% are independent predictors of SCH.