| Level mg/dL | Level mmol/L | Interpretation |
| < 200 | < 5.0 | Desirable level corresponding to lower risk for heart disease |
| 200–240 | 5.2–6.2 | Borderline high risk |
| > 240 | > 6.2 | High risk |
However, as today's testing methods determine LDL ("bad") and HDL ("good") cholesterol separately, this simplistic view has become somewhat outdated. The desirable LDL level is considered to be less than 100 mg/dL (2.6 mmol/L)[28], although a newer target of < 70 mg/dL 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. Of note, typical LDL values for children before fatty streaks begin to develop is 35 mg/dL.
Most testing methods for LDL do not actually measure LDL in their blood, much less particle size. For cost reasons, LDL values have long been estimated using the Friedewald formula:
[total cholesterol] - [total HDL] - 20% of the triglyceride value = estimated LDL.
The basis of this is that Total cholesterol is defined as the sum of HDL, LDL, and VLDL. Ordinarily just the total, HDL, and triglycerides are actually measured. The VLDL is estimated as one-fifth of the triglycerides. It is important to fast for at least eight hours before the blood test because the triglyceride level varies significantly with food intake.
Given the well-recognized role of cholesterol in cardiovascular disease, it is surprising that some studies have shown an inverse correlation between cholesterol levels and mortality in subjects over 50 years of age—an 11% increase overall and 14% increase in CVD mortality per 1 mg/dL per year drop in cholesterol levels. In the Framingham Heart Study, the researchers attributed this phenomenon to the fact that people with severe chronic diseases or cancer tend to have below-normal cholesterol levels. This explanation is not supported by the Vorarlberg Health Monitoring and Promotion Programme, in which men of all ages and women over 50 with very low cholesterol were increasingly likely to die of cancer, liver diseases, and mental diseases. This result indicates that the low cholesterol effect occurs even among younger respondents, contradicting the previous assessment among cohorts of older people that this is a proxy or marker for frailty occurring with age.
A small group of scientists, united in The International Network of Cholesterol Skeptics, continues to question the link between cholesterol and atherosclerosis. However, the vast majority of doctors and medical scientists accepts the link as fact.
Low levels of cholesterol or 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. Generally, the low cholesterol levels seem to be a consequence of an underlying illness, rather than a cause.
Cholesterol testing
It is recommended to test cholesterol every 5 years for people aged 20 years or older. A blood sample taken after fasting is taken by a doctor or a home cholesterol monitoring device to determine a lipoprotein profile. This measures total cholesterol, LDL (bad) cholesterol, HDL (good) cholesterol and triglycerides. It is recommended to have cholesterol tested more frequently than 5 years if a person: has total cholesterol of 200 mg/dL or more, if a man over age 45 or a woman over age 50, has HDL (good) cholesterol less than 40 mg/dL, or other risk factors for heart disease and stroke.