MON-613 Lipid Abnormalities In Thyroid Dysfunction.

Abstract

The relationship between thyroid hormone levels and lipid disorders was first described decades ago when physicians relied on laboratory data from older assays. From these studies, the association between thyroid hormone levels and low-density lipoprotein-cholesterol (LDL-C) was well established. However, little data exists assessing the relationship between modern thyroid assays and lipid levels as well as lipoproteins other than LDL-C. We hypothesized that thyroid dysfunction affects all lipids and lipoproteins with substantial variability between patients. We queried the electronic medical records of a large county hospital in Dallas, TX assessing all patients who had thyroid function tests (TSH and Free T4) and lipid panels done on the same day from 1/1/2013 to 1/1/2018. We stratified test results into hypothyroid (TSH > 4.5 mcIU/L and Free T4 < 0.8 ng/dL), hyperthyroid (TSH < 0.5 mcIU/L and Free T4 > 1.8 ng/dL) and normal (0.5 ≤ TSH ≤ 4.5 mcIU/L, 0.8 ≤ Free T4 ≤ 1.8 ng/dL). Results consistent with subclinical hyper- and hypothyroidism were excluded. Each group was analyzed and compared for triglycerides, total cholesterol, HDL-C, non-HDL-C and LDL-C levels. Our query identified 25,290 unique results for thyroid hormones and lipid panels checked on the same day. Of these, 2,918 (11.5%) were hypothyroid (mean TSH 41 mcIU/L, Free T4 0.6 mcIU/L), 1,152 (4.5%) were hyperthyroid (mean TSH 0.08 mcIU/L, FT4 2.7 mcIU/L), and 23,332 (92.2%) were normal (mean TSH 2.0 mcIU/L, FT4 1.2 mcIU/L). Overall, the hypothyroid group had the highest levels of lipids/lipoproteins: total cholesterol mean (SD) hypothyroid 232 (93) vs normal 186 (51) vs hyperthyroid 155 (42) mg/dL, p < 0.001; LDL-C 126 (49) vs 103 (36) vs 83 (31) mg/dL, p < 0.001; non-HDL-C 179 (91) vs 133 (46) vs 107 (36) mg/dL, p < 0.001; triglycerides median (IQR) 163 (114, 273) vs 123 (118, 184) vs 101 (78, 144) mg/dL, p < 0.001. HDL-C was slightly lower in both hypothyroid and hyperthyroid groups: 49 (19) vs 51 (16) vs 47 (16), p < 0.001. Among the hypothyroid, 8% (n = 229) had triglycerides levels ≥ 1000 mg/dL, and 10% (n = 284) had LDL-C ≥ 190 mg/dL without increased triglycerides. Our results confirm that thyroid dysfunction affects all lipids and lipoproteins: all but HDL-C were increased in hypothyroidism and decreased in hyperthyroidism. Additionally, we found that among hypothyroid patients, variability may exist in the lipid response to thyroid hormone. Some patients developed hypertriglyceridemia, placing them at risk for pancreatitis, while other patients were found to have severe hypercholesterolemia, potentially increasing their risk of coronary artery disease. Our results reinforce the need to check all hypothyroid patients for abnormalities in lipid and lipoproteins. Additional work is required to understand why a variability in lipid response may exist.