levels can get altered for many reasons and thyroid
problems are one such reason. Since your thyroid is normal with treatment, your LDL abnormality is unlikely due to thyroid. Other reasons it can get elevated are aging, lack of exercise, renal problem, liver
problem , diabetes
, genetic and much more.
Again you need not be worried by LDL level alone and it has to be collectively seen along with other cholesterol levels and patients clinical profile.