We also analysed which of these parameters predict SCH risk and constitute independent markers. 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. Several cardiovascular risk factors have been analysed, but yielded controversial results. Subclinical hypothyroidism (SCH) has been suggested to be associated with increased cardiovascular risk by different mechanisms. Previous studies had limitations in the control of potential confounding factors and further studies should consider those factors. Subclinical hypothyroidism may correlate with altered lipid profile. Potential publication bias was found in TC and LDL-C analysis by the Egger test or Begg test and was not confirmed by the trim and fill method. Match strategy was the main source of heterogeneity among studies in TC and LDL-C analysis. No significant difference was observed for serum high-density lipoprotein cholesterol (HDL-C). Meta-analysis suggested that the serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and total triglyceride levels were significantly increased in patients with subclinical hypothyroidism compared with euthyroidism individuals the WMD were 12.17 mg/dl, 7.01 mg/dl, and 13.19 mg/dl, respectively (P<0.001 for all). Sixteen observational studies were included in our analysis. Meta-regression was used to explore the source of heterogeneity among studies, and the Egger test, Begg test, and the trim and fill method were used to assess potential publication bias. We included articles reporting the relationship between subclinical hypothyroidism and at least 1 parameter of lipid profiles, and calculated the overall weighted mean difference (WMD) with a random effects model. Dissertation databases (PQDT and CDMD) were searched for additional unpublished articles. We searched PubMed, Cochrane Library, and China National Knowledge Infrastructure articles published January 1990 through January 2014. We performed a meta-analysis to investigate the association between subclinical hypothyroidism and lipid profiles.
Previous studies yielded controversial results about the alteration of lipid profiles in patients with subclinical hypothyroidism. Thus, there is no "threshold value" of TSH in these patients per se necessitating substitution therapy with thyroxine. Within the group of subjects with subclinical hypothyroidism there was no apparent relationship between serum concentrations of TSH ranging from 4.0 to 49.0 microU/mL and concentrations of LDL cholesterol.
Serum concentrations of LDL cholesterol were similar in euthyroid persons (134+/-39 mg/dL) and in patients with subclinical hypothyroidism (137+/-40 mg/dL) but were higher (178+/-70 mg/dL, p < 0.01) in overt hypothyroidism. Because an unfavorable lipid profile would provide a possible explanation for the reported association of coronary-heart disease with this syndrome, we have evaluated the relationship of thyrotropin (TSH) with total cholesterol, low-density-lipoprotein (LDL) cholesterol, and triglycerides in patients with normal thyroid function (n = 4886) as well as subclinical (n = 1055) and manifest (n = 92) hypothyroidism. The significance of subclinical hypothyroidism in regard to ensuing hyperlipidemia remains unclear.
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