Non High Density Lipoprotein Cholesterol, a Simple and Reliable Marker to Assess Cardiovascular Disease Risk in Hypothyroid Patients

Abstract

Introduction: Thyroid hormones regulate growth, metabolism and cellular differentiation in our body. Thyroid disorders are among the commonly encountered endocrinopathies across the globe in the recent past. Hypothyroidism is prevalent to the extent of 9.45-11.73% among urban inland regions of India as reported in a recent survey. Thyroid hormones influence lipid metabolism. The dyslipidemia in hypothyroidism presents as high serum Total Cholesterol (TC) levels, elevated Low Density Lipoprotein-Cholesterol (LDL-C) levels, hypertriglyceridemia and Increased Triglyceride (TGL)- Rich Lipoproteins or Remnant Lipoproteins (RLPs). Non High Density Lipoprotein-Cholesterol (Non-HDL-C) reflects the cholesterol content of these RLPs. The potential of Non-HDL-C seems to be underutilised in patients with hypothyroidism. Aim: To know the levels of Non-HDL-C in hypothyroid patients as compared to normal subjects and to assess its reliability to predict the future cardiovascular risk in hypothyroid patients. Materials and Methods: The study was a case-control study, that was conducted in District Hospital, Chamarajanagar, Karnataka, India, between December 2019 to September 2020, involving two groups. The first group were the cases, consisting of 50 hypothyroid patients between 18 and 55 years of age, 50 healthy age and sex matched controls were selected and inducted into this study. The ‘Case group was further divided into “Known cases” and ‘New cases’, based on the disease course. The ‘New cases’ are further classified into group of ‘Overt Hypothyroids’ and ‘Subclinical hypothyroids’. In all the subjects of present study, serum TC and serum HDL- Cholesterol (HDL-C) was estimated. The value of HDL-C was subtracted from TC level and Non-HDL-C level was calculated for all the study subjects. The values of the lipid fractions in both groups and in the subgroup were tabulated and compared using suitable statistical tool. Results: In the present study it was noted that Non-HDL-C was significantly high in hypothyroid patients when compared to healthy controls (p=0.02). Also, the newly diagnosed hypothyroid patients had significantly high Non-HDL-C levels than controls (p=0.01). The subgroup of ‘Known cases’ who were on Levo- thyroxine replacement did not show significantly elevated Non- HDL-C levels. Overt Hypothyroid (OH) patients had higher values of Non-HDL-C than those with Subclinical Hypothyroidism (SCH). Conclusion: At each level of the present study, (controls vs cases, known vs new cases and OH vs SCH) non-HDL-C has emerged in an expected pattern, which is consistent with pathophysiology, course and severity of the disease. Therefore, present study suggest the feasibilty of non-HDL-C replacing the traditional lipid profile assays for assessment of dyslipidemia in hypothyroid patients.