Fasting vs Nonfasting Cholesterol
Serum cholesterol measurement is one of the most conducted blood tests. Diabetes, heart attacks, strokes and narrowing of arteries are on the rise, and the World Health Organization has recommended serum cholesterol as one of the assessment tools used to determine the risk of having an ischemic heart disease. Apart from this, very valid reason many people get their cholesterol levels checked often so they can control it with diet and drugs as needed. These tests are very important to the apparently healthy individuals as well as the heart patients. It is always worthwhile to know the slight differences between the two tests.
Fasting and non-fasting cholesterol levels are based upon the general body metabolism, especially cholesterol metabolism. Our diet contains cholesterols and fatty acids. Fat components get emulsified and broken down in the small intestine. Fats break up into fatty acids, glycerol and cholesterols. Cholesterol is fat soluble, so it passes into the intestinal lining cells directly. Inside the cells, cholesterols and fatty acids get compacted into chylomicrons. As chylomicrons, cholesterol gets transported into the splanchnic circulation and then into the liver. Liver takes up the cholesterol in chylomicrons. Liver also synthesizes cholesterol using an enzyme called HMGCoA reductase, which is very active at night. That is why doctors prescribe statins (HMGCoA reductase inhibitors) at night. Liver forms very low density lipoproteins (LDL) which contains a lot of fatty acids and glycerol. At capillaries in end organs, these very low density lipoproteins get broken down partially, and some of the fatty acids and glycerol get absorbed. The result is intermediate density lipoproteins. At end organs, cells produce cholesterol. These cholesterols get transferred onto intermediate density lipoproteins forming high density lipoproteins (HDL). These bring cholesterol back to the liver for recirculation. The liver is a hub that brings all the synthetic and catabolic pathways together. Fasting is an important modulator of all these pathways. Fasting spends all readily available glucose from the liver within minutes. Then glycogen breakdown commences. After about half an hour, fat breakdown starts. The enzymes that breakdown very low density lipoproteins get deactivated and hormone sensitive lipase located inside fat cells get activated. Therefore, broken down fat goes to the liver as substrates for gluconeogenesis; also known as synthesis of new glucose.
Fasting cholesterol level testing, or to be more precise, fasting lipid profile, assesses these catabolic and anabolic pathways. Fasting blood cholesterol testing needs 12 hours of fasting. Fasting tends to increase the levels of very low density lipoproteins (VLDL), low density lipoproteins, and lower high density lipoproteins. If the body is capable of good fat metabolism, these levels should be under control. The risk of high levels of low density lipoproteins is that it increases the occurrence of arterial hardening and atheromatous plaque formation. Fasting is a method used to assess these internal mechanisms. However,recent studies say that fasting is not essential. It does not make a big difference in blood glucose levels. In general, total cholesterol should be less than 200mg/dl. LDL should be below 100 mg/dl and HDL should be above 50 mg/dl.
Non-fasting serum cholesterol level is easy to do. Many disease conditions and the diet alter blood cholesterol levels. It is difficult to give cut off lines for individual components of the non-fasting lipid profile due to variations in metabolisms from person to person. In general, total non-fasting serum cholesterol should be below 200 mg/dl. This value is similar to fasting total cholesterol because fasting actually does not have much of an impact on total lipid levels. According to recent studies, fasting is not essential and no significant variability of non-fasting cholesterol. Therefore, fasting lipid profile is the recommended test. Non-fasting test usually gives the total lipid levels and not a full profile.
What is the difference between Fasting and Nonfasting Cholesterol?
• Fasting lipid profile assesses the metabolic pathways accurately while non-fasting lipid profile does not, due to metabolic variation.
• Lipid profile needs fasting and gives values for each individual component of the fat metabolic pathway while non-fasting cholesterol assesses the total lipid level only.