Subclinical hypothyroidism and cardiovascular risk

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.

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.

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.

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).

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.