A lipoprotein is a complex of one or more lipids bound to one or more proteins. In humans, lipoproteins transport water-insoluble fats in the blood and are classified by their density: very-low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs) and high-density lipoproteins(HDLs).
Cholesterol is carried through the bloodstream by lipoproteins. Healthwise, LDLs are known as "bad" cholesterol and HDLs are known as "good" cholesterol. When your doctor measures your cholesterol, he/she takes readings of the different types of cholesterol in your blood:
LDL Cholesterol
- Desirable: less than 130 mg/dl
- Borderline High: 130-159 mg/dl
- High: more than 160 mg/dl
HDL Cholesterol
- Desirable: more than 35 mg/dl
- Risk Level: less than 35 mg/dl
The information in this writeup was taken from the science dictionary at http://biotech.icmb.utexas.edu/; I oversaw the development of the dictionary (the website was mothballed in 1998) and I believe I wrote the entry this is based on.