Elevated serum lipoprotein(a) in subclinical hypothyroidism

Asymptomatic lymphocytic thyroiditis and subclinical hypothyroidism are associated with increased risk for coronary artery disease. The present study aimed at evaluating serum lipoprotein(a)(Lp(a)), measured as apo(a), and other lipid parameters in 32 subjects with asymptomatic subclinical hypothyroidism.

Thirty-two Chinese subjects with asymptomatic subclinical hypothyroidism were compared to 96 age and sex-matched healthy controls.

Subclinical hypothyroid patients had higher (P < 0.005) apo(a), total triglyceride (TG), total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) but lower (P < 0.05) high density lipoprotein cholesterol (HDL-C) levels compared with sex and age-matched controls (apo(a) 296 (48-1650) vs 182 (19-1952 U/l), geometric mean (range); TG 1.86 +/- 0.94 vs 1.33 +/- 0.74 mmol/l (mean +/- SD); TC 6.10 +/- 1.17 vs 5.42 +/- 1.13 mmol/l; LDL-C 4.10 +/- 1.00 vs 3.49 +/- 0.96 mmol/l; HDL-C 1.15 +/- 0.40 vs 1.34 +/- 0.40 mmol/l, respectively). APo A-I and apo B were also higher than controls (1.96 +/- 0.48 vs 1.48 +/ 0.29 g/l and 1.44 +/- 0.42 vs 1.05 +/- 0.29 g/l, respectively). Total cholesterol/HDL ratio and LDL/HDL ratio were also elevated in these subjects (5.77 +/- 1.96 vs 4.28 +/- 1.19 and 3.89 +/- 1.41 vs 2.79 +/- 0.97, respectively, both P < 0.0005). Individual analysis revealed that 16 (50%) subjects had hyperlipoproteinaemia (TC > 5.2 mmol/l in 10; TC > 5.2 mmol/l and TG > 2.3 mmol in six) as compared to 21(20.8%) in the control group (P < 0.005). Subjects with TSH > or = 11.0 mIU/l had significantly higher TC/HDL and LDL/HDL ratios. A significant correlation was observed between TSH levels and TC/HDL ratios (r = 0.455, P < 0.01).

Subclinical hypothyroidism is associated not only with elevated LDL-cholesterol levels and low HDL-cholesterol levels but also with elevated lipoprotein (a). This may further increase the risk development of atherosclerosis.