Ask Dr. H: Cholesterol fluctuates often

Question:

I am a thin, 55-year-old female in good health other than mild treated hypothyroidism. My cholesterol profile just two months ago showed an LDL ("bad") cholesterol level of 79. I just received results showing an LDL of 94 from the same lab. I have not changed anything in my diet. What on earth could cause such an increase and is it cause for alarm?

Answer: Both LDL values are fine for you and shouldn't be a cause for worry.

Total cholesterol and LDL "bad" cholesterol values are known to fluctuate both from day to day and from hour to hour.

A study published in the August 1990 issue of the Archives of Internal Medicine analyzed three blood samples drawn over five days from each of 51 subjects. Random samples were sent to the Centers for Disease Control and Prevention to confirm accuracy.

A second study also published in the August 1990 Archives of Internal Medicine analyzed weekly fasting blood samples from 20 subjects over a four-week period. Each sample was sent for cholesterol analysis to two different labs and run five times in each lab.

These studies revealed two important points about cholesterol fluctuation: (1) There is substantial day-to-day variability in total cholesterol. Eighty percent of the 20 subjects in the second study had total cholesterol fluctuations in excess of 30 points; and (2) Most fluctuations reflect true biologic variability. Variability due to lab error never exceeded 3 percent.

Cholesterol in the blood comes about not only from the foods we eat, but our own body's production by the liver. The amount of cholesterol produced by the liver can vary from hour to hour. Also, a slightly longer or shorter overnight fast before getting morning bloodwork can lower or elevate cholesterol levels. For this reason, it's best to get multiple measurements over time so as not to overestimate or underestimate one's cardiovascular risk.