What could cause a sudden rise in LDL cholesterol in young adults who have not changed their lifestyle or started any new medications?

Depending on the degree of the rise in LDL-C noted, there are a number of reasons.

Despite the person reporting that they have "not changed their lifestyle," one must consider either reduced activity or a diet with more saturated fat, due to being less diet-conscious, or due to a low-carbohydrate or...

My first response to a large change in LDLC would be to repeat in 2-3 weeks (it is not an emergency) because I have seen several patients who have widely fluctuating LDLC levels for no apparent reason. If the repeat lab is more like prior results (before the spike), it would suggest a lab variation ...

I would be evaluating this patient for secondary causes, especially things that would have changed recently. I would review the diet more closely as I've seen patients, especially lean individuals, go on a keto diet resulting in a significant increase in their LDL-C. I would want to otherwise rule o...