Cholesterol, LDL

Clinical significance

LDL cholesterol testing is an important part of a CHD prevention strategy. It is used to further assess the risk of CHD when total cholesterol and/or HDL cholesterol results are abnormal. LDL cholesterol is also used to monitor patients with prior CHD, other atherosclerotic disease, or diabetes mellitus.
From a practical standpoint, assessing a patient's CHD risk should encompass the measurement of total cholesterol, LDL-cholesterol, and HDL-cholesterol. Risk tables listing Elevated levels of LDL indicate risk for heart disease. Treatment (with diet or drugs) for high LDL aims to lower LDL to a target value based on a overall risk of heart disease. The target value is:
• LDL less than 2.6 mmol/L (100 mg/dL) in the case of having heart disease or diabetes.
• LDL less than 3.4 mmol/L (130 mg/dL) in the case of having 2 or more risk factors.
• LDL less than 4.2 mmol/L (160 mg/dL) in the case of having 0 or 1 risk factor.

LDL cholesterol is the primary target of therapy. Follow-up LDL determination should be made 4 to 6 weeks after initiating drug therapy and again at 3 months. A minimum of 2 lipoprotein determinations is essential for evaluating the efficacy of a given drug dose. The mean of these 2 determinations and a careful assessment of drug adherence should be used to judge the efficacy of drug treatment. After the target LDL cholesterol concentration has been achieved, patients should be followed up every 4 months, or more frequently depending on the drug being used, to monitor cholesterol levels and possible side effects.

LDL-cholesterol/HDL-cholesterol ratios and total cholesterol/HDL-cholesterol ratios are available from the Framingham Study.(112)

LDL cholesterol/HDL cholesterol risk ratio
  One-half average
3,553,22Twice average
6,255,03Three times average

This risk ratio is not valid if:
1. Chylomicrons are present and
2. Serum triglyceride is greater than 4.52 mmol/L (400 mg/L).

Using these tables is the most meaningful way to assess CHD risks. The measurement of triglycerides is primarily performed for LDL-cholesterol calculations using the Friedewald formula.
It should be stressed that the measurement of cholesterol alone should be utilized only as a screening method to detect hypercholesterolemia. It is especially important that cholesterol concentrations in the range of 5.98 to 7.54 mmol/L (230 to 290 mg/dl) be followed with the measurement of LDL- cholesterol and HDL-cholesterol levels.

Pathologic changes in the concentration of LDL-cholesterol
Increased concentration of LDL-cholesterol inDecreased concentration of LDL-cholesterol in
• acute intermittent porphyria
• acute myocardial infarction
• adrenal cortical hyperfunction (glucocorticoid excess)
• Cancer of liver
• carotid artery stenosis
• chronic renal failure
• coronary artery disease
• Diabetes mellitus
• essential hypertension
• essential hypertension
• growth hormone deficiency
• heart transplantation
• hypercholesterolemia
• hyperlipidemia
• hypopituitarism
• hypothyroidism
• insulin-dependent diabetes mellitus (IDD)
• nephrotic syndrome
• noninsulin-dependent diabetes mellitus (NIDD)
• peripheral arterial disease
• postmenopause
• renal transplantant rejection
• renal transplantation
• acquired immune deficiency syndrome (AIDS)
• acute cholecystitis
• affective disorders
• alcoholism
• celiac disease
• Chron’s disease
• chronic renal failure
• cirrhosis of liver
• HIV 1 infection
• hyperthyroidism
• rheumatoid arthritis