Would it change your diagnosis if you had been tested
in summer?
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After controlling for relative plasma volume, the amplitude
of seasonal variation in blood lipid levels decreased
statistically significantly, with a greater effect
attributable to relative plasma volume in men. During the
summer, the increase in environmental temperature or
physical activity, or most likely a combination of the two,
could be contributing to a hemodilution effect, with an
accompanying apparent decrease in blood lipid levels. The
underlying mechanism could be mobilization of fluid from
the interstitial to the intravascular compartment due to
heat acclimatization.31-33 Plasma hypervolemia during
physical training has been associated with 2 major factors:
an elevation in renin activity and vasopressin levels
during exercise, which facilitates sodium and water
retention, and a progressive, chronic increase in plasma
albumin content, which provides increased blood-water
binding capacity.34-36 The fact that the HDL cholesterol
concentration was not as affected by changes in plasma
volume could be related to the complex interactions between
seasonal changes in physical activity. Reductions in HDL
cholesterol levels in the warmer months as a consequence of
hypervolemia may have been counterbalanced by increased HDL
cholesterol concentrations resulting from increased
physical activity levels in the summer.
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