A patient is lipemic after a 24-hour fast. This is mainly due to elevation in which molecule?

The primary cause of lipemia after a 24-hour fast is an elevation in VLDL (Very Low-Density Lipoproteins). During fasting, the body relies on stored fat for energy, primarily through the action of lipolysis, which releases free fatty acids into the bloodstream. The liver responds to this increase in fatty acids by synthesizing and releasing VLDL into circulation, as VLDL is a key transport vehicle for endogenous triglycerides.

VLDL levels can be particularly elevated when the body is in a state where fat mobilization is enhanced, such as during fasting. As VLDL carries a significant amount of triglycerides, its increased presence in the blood contributes to the observed lipemia.

Chylomicrons, on the other hand, are primarily responsible for carrying exogenous lipids from the intestine after meals, hence their levels are typically low after fasting as there are no dietary fats to transport. LDL and HDL levels are also less likely to be the predominant contributors to lipemia in this fasting scenario, as they primarily transport cholesterol and other lipids rather than the triglycerides that cause the lipemic appearance in the serum.