< 5.2 desirable level(lower risk) 200–240 5.2–6.2 borderline high risk > 240 > 6.2 high risk the 1987 report of national cholesterol education program, adult treatment panels suggests the total blood cholesterol level should be: < 200 mg/dl normal blood cholesterol, 200–239 mg/dl borderline-high, > 240 mg/dl high cholesterol. the american heart association provides a similar set of guidelines for total (fasting) blood cholesterol levels and risk for heart disease: statins are effective in lowering ldl cholesterol and widely used for primary prevention in people at high risk of cardiovascular disease, as well as in secondary prevention for those who have developed cardiovascular disease. more current testing methods determine ldl ("bad") and hdl ("good") cholesterol separately, allowing cholesterol analysis to be more nuanced. the desirable ldl level is considered to be less than 100 mg/dl (2.6 mmol/l), although a newer upper limit of 70 mg/dl (1.8 mmol/l) can be considered in higher-risk individuals based on some of the above-mentioned trials. a ratio of total cholesterol to hdl—another useful measure—of far less than 5:1 is thought to be healthier. reference ranges for blood tests, showing usual, as well as optimal, levels of hdl, ldl, and total cholesterol in mass and molar concentrations, is found in orange color at right, that is, among the blood constituents with the highest concentration. total cholesterol is defined as the sum of hdl, ldl, and vldl. usually, only the total, hdl, and triglycerides are measured. for cost reasons, the vldl is usually estimated as one-fifth of the triglycerides and the ldl is estimated using the friedewald formula (or a variant): estimated ldl = − − . direct ldl measures are used when triglycerides exceed 400 mg/dl. the estimated vldl and ldl have more error when triglycerides are above 400 mg/dl. in the framingham heart study, each 10 mg/dl (0.6 mmol/l) increase in total cholesterol levels increased 30-year overall mortality by 5% and cvd mortality by 9%. while subjects over the age of 50 had an 11% increase in overall mortality, and a 14% increase in cardiovascular disease mortality per 1 mg/dl (0.06 mmol/l) year drop in total cholesterol levels. the researchers attributed this phenomenon to reverse causation, whereby the disease itself increases risk of death, as well as changes a myriad of factors, such as weight loss and the inability to eat, which lower serum cholesterol. this effect was also shown in men of all ages and women over 50 in the vorarlberg health monitoring and promotion programme. these groups were more likely to die of cancer, liver diseases, and mental diseases with very low total cholesterol, of 186 mg/dl (10.3 mmol/l) and lower. this result indicates the low-cholesterol effect occurs even among younger respondents, contradicting the previous assessment among cohorts of older people that this is a marker for frailty occurring with age. hypocholesterolemia abnormally low levels of cholesterol are termed hypocholesterolemia. research into the causes of this state is relatively limited, but some studies suggest a link with depression, cancer, and cerebral hemorrhage. in general, the low cholesterol levels seem to be a consequence, rather than a cause, of an underlying illness. a genetic defect in cholesterol synthesis causes smith–lemli–opitz syndrome, which is often associated with low plasma cholesterol levels. hyperthyroidism, or any other endocrine disturbance which causes upregulation of the ldl receptor, may result in hypocholesterolemia. cholesterol testing the american heart association recommends testing cholesterol every 4–6 years for people aged 20 years or older. a separate set of american heart association guidelines issued in 2013 indicates that people taking statin medications should have their cholesterol tested 4–12 weeks after their first dose and then every 3–12 months thereafter. for men ages 45 to 65 and women ages 55 to 65, a cholesterol test should occur every 1-2 years, and for seniors over age 65, an annual test should be performed. a blood sample after 12-hours of fasting is taken by a healthcare professional from an arm vein to measure a lipid profile for a) total cholesterol, b) hdl cholesterol, c) ldl cholesterol, and d) triglycerides. results may be expressed as "calculated", indicating a calculation of total cholesterol, hdl, and triglycerides. cholesterol is tested to determine for "normal" or "desirable" levels if a person has a total cholesterol of 5.2 mmol/l or less (200 mg/dl), an hdl value of more than 1 mmol/l (40 mg/dl, "the higher, the better"), an ldl value of less than 2.6 mmol/l (100 mg/dl), and a triglycerides level of less than 1.7 mmol/l (150 mg/dl). blood cholesterol in people with lifestyle, aging, or cardiovascular risk factors, such as diabetes mellitus, hypertension, family history of coronary artery disease, or angina, are evaluated at different levels. interactive pathway map click on genes, proteins and metabolites below to link to respective articles. [[file: |alt=statin pathway edit]] statin pathway edit the interactive pathway map can be edited at wikipathways: "statin_pathway_wp430". cholesteric liquid crystals some cholesterol derivatives (among other simple cholesteric lipids) are known to generate the liquid crystalline "cholesteric phase". the cholesteric phase is, in fact, a chiral nematic phase, and it changes colour when its temperature changes. this makes cholesterol derivatives useful for indicating temperature in liquid-crystal display thermometers and in temperature-sensitive paints. stereoisomers natural cholesterol (top) and ent-cholesterol (bottom) cholesterol has 256 stereoisomers that arise from its eight stereocenters, although only two of the stereoisomers have biochemical significance (nat-cholesterol and ent-cholesterol, for natural and enantiomer, respectively), and only one occurs naturally (nat-cholesterol). additional images cholesterol units conversion steroidogenesis, using cholesterol as building material space-filling model of the cholesterol molecule numbering of the steroid nuclei