The total cholesterol in your blood is not a measure of a single value. The number, on its own, is an incomplete picture of your overall risk of heart disease and other complications. There is “good” cholesterol and “bad” cholesterol, and if your total is high, it may mean that you have above-average levels of good cholesterol. Triglycerides, another fat in the blood, also indicate a possible increased risk of heart disease, so an accurate analysis of your overall risk level can only be determined by a lipoprotein profile, which takes all three of these elements into account.
In 1913, rabbits fed a diet high in cholesterol displayed an increased incidence of atherosclerosis, leading researchers to link cholesterol to heart disease. The study was criticized for using animals that ate a predominantly vegetarian diet that contained no cholesterol, so it was unclear whether the cholesterol was to blame or the increase in lesions was due to a dietary change the rabbits were ill-equipped to handle. Testing was unable to determine the highest cholesterol readings for which there were no ill-effects, however.
Further studies involving dogs and cats demonstrated no such link between cholesterol and atherosclerotic lesions, but dogs and cats metabolize cholesterol into easily excretable bile acids, so the study sample was again imperfect. The theory finally gained traction when the results from the rabbit test were reproduced in rats, and some in the medical establishment moved toward warnings that high cholesterol led to increased risk of heart disease. It wasn’t until 1969, however, that the American Heart Association proclaimed that individuals with high cholesterol should be treated medically, and doing so would decrease incidents of acute fatal heart attacks. They were roundly criticized by cardiologists who claimed there was no demonstrable link, and who published those contrary opinions in medical journals well into the 1970s. The National Institutes of Health set out to determine once and for all if a link existed, and in 1984, it gave the results of its decade-long double-blind trials in a consensus statement, proclaiming emphatically that high blood cholesterol led to an increased risk of heart disease.
Cholesterol testing involves drawing blood from the patient and subjecting that blood to an analysis for either total cholesterol or a lipid profile. Clinical profiles are determined by separating the lipids from the rest of the blood by means of a centrifuge, or an instrument that spins the blood and subjects it to centrifugal force. There are home-testing kits widely available, and some are able to separate the good, or HDL, and bad, or LDL, numbers. Patients, whether testing at home or with a physician, should fast for roughly 12 hours prior to taking a cholesterol test. Even clinical testing can result in dramatic variability, so you should check your levels several times over a one-year period. In practice, there is no highest cholesterol number achievable on standard tests. There are, however, scales that stop at various levels above the "high" mark of 240 mg/dL, or milligrams per deciliter. Often, 350 is the highest total cholesterol reading on such tests.
A total cholesterol level below 200 mg/dL is considered desirable by the American Heart Association. Readings between 200 and 239 are considered borderline, while readings above 240 are considered elevated. Certain individuals carry a genetic trait that predisposes them to high cholesterol levels, regardless of diet. The condition, known as familial hypercholesterolemia, produces the highest cholesterol readings. Some sufferers who inherit the condition-causing gene from both parents can record total cholesterol levels as high as 1000 mg/dL. Patients with readings that high often die in their 20s, according to CNN Health.
The American Heart Association warns people with total cholesterol over 240 mg/dL or LDL above 160 mg/dL that they are at risk for heart disease and stroke without dietary or pharmacological intervention. It is possible to reduce cholesterol levels with diet therapy alone, but drugs like Lipitor are often prescribed in conjunction with diet recommendations.