Unusual over 100. Hdl cholesterol (hdl-c) levels over 100 are vary uncommon. In general, high hdl-c may be the result of genetics (hyperalphalipoproteinemia), exercise, increased alcohol intake, or medications (niacin, fibrates). Rare causes include obstruction in the biliary tract, very high blood levels of dilantin, and organophosphate toxicity.
No. Hdl (high-density lipoprotein) isn't really a cholesterol measurement to begin with....It's a carrier protein that assists in transporting away and decreasing risk of cholesterol deposits in blood vessel walls. There are no studies indicating a "dangerously" high level, but, of course, a high HDL is a great heart protective measurement.