HDL Cholesterol: Reference Range, Interpretation, Collection And ...

Description

HDL-C, which consists mostly of cholesterol, phospholipid, and protein, is produced and secreted by the liver and intestine. [9]

HDL-C transports cholesterol from tissues to the liver. In this reverse cholesterol transport process, it performs a "cleanup" function. This process is called reverse cholesterol transport because cholesterol synthesized in peripheral tissues is eventually returned to the liver for its disposal from the body. Notably, HDL-C concentrations do not directly indicate the efficiency or the extent of reverse cholesterol transport. [4]

HDL-C has many surface proteins. ApoA1 and apoA2 proteins on HDL-C are derived by direct secretion from the liver. [10] ApoA1 synthesis is necessary to produce HDL-C. Mutations in the apoA1 gene that cause HDL-C deficiency are associated with accelerated atherogenesis. Overexpression of apoA1 in the mouse model protects against experimentally induced atherogenesis. [11] Additionally, HDL-C may protect against atherogenesis by mechanisms not directly related to reverse cholesterol transport. These functions include putative anti-inflammatory, anticoagulant, antioxidative, platelet anti-aggregatory, and profibrinolytic activities. [12]

High levels of HDL-C are desirable because of their inverse relation with coronary risk. HDL-C is called good cholesterol because it is inversely related to the incidence of atherosclerosis. However, emerging scientific evidence has shown that paradoxically, very high levels of HDL-C (> 80 mg/dL) were linked with a higher risk for all-cause and cardiovascular mortality in populations with coronary heart disease compared with those with normal HDL-C levels (40-60 mg/dL), independent of conventional cardiovascular risk factors and alcohol consumption. Heterogeneity in HDL-C particles and possible changes in HDL-C functionality from anti-inflammatory to pro-inflammatory under certain conditions, such as elevated oxidative stress, may be the underlying causes of these adverse outcomes. [13]

Indications/Applications

HDL-C is used in the assessment of coronary or other vascular pathology risks.

Considerations

Recent illness, starvation and stress, medications such as thiazide diuretics and steroids, hypertriglyceridemia, and elevated immunoglobin levels are associated with reduced HDL-C levels.

Statins or 3-hydroxy-3-methylglutaryl coenzyme A i.e., HMG-CoA reductase inhibitors modestly increase HDL-C levels. The mild rise in HDL-C levels from these drugs may be related to the inhibition of ρ-signaling pathways with activation of peroxisome proliferator–activated receptor α. Increases in HDL-C levels may also be attributable to decreasing plasma CETP activity by statins. [14]

A study by Pitanga et al reported that although a positive association was found between leisure time physical activity in adults and greater HDL-C levels, males require more physical activity than females to demonstrate such increases. In females, it was noted, walking and moderate or vigorous physical activity correlated with raised HDL-C levels, while in males, only vigorous exercise was associated with a rise in HDL-C. It was suggested that this may be partly because males have higher resting homeostasis parameters (e.g., heart rate, blood pressure, glycemic levels, caloric expenditure) than females; therefore, males may require a greater amount of physical activity to disrupt resting homeostasis and activate the physiological means of cardiovascular protection such as an HDL-C increase. [15]

A pooled analysis by the Non-Communicable Disease Risk Factor Collaboration of 458 population-based studies covering 23 Asian and Western countries determined that in a number of Western nations, as well as in Japan and South Korea, the mean ratio of total-to-HDL cholesterol has declined since 1980, with the reduction in Swiss males being approximately 0.7 per decade between 1980 and 2015. (In contrast, China saw an increase in the ratio.) Also, from about 1980 to 2015, HDL-C levels in Japan and South Korea saw a per-decade rise of between 0.04 mmol/L (South Korean males) and 0.17 mmol/L (Japanese females). [16]

Millions of people are affected by infertility globally. Recently published study by Li et al utilizing NHANES data showed elevated levels of non high density lipoprotein to high density lipoprotein ratio (NHHR) are associated with high risk of infertility in some specific groups. [17]