LDL Cholesterol Calculator

Low-density lipoprotein (LDL) cholesterol is often called "bad" cholesterol. It carries cholesterol to tissues and can deposit in arterial walls, leading to atherosclerosis. Elevated LDL is a major risk factor for cardiovascular disease.

The Friedewald formula calculates LDL as: LDL = Total Cholesterol – HDL – (Triglycerides / 5). It is the most commonly used method but is only valid when triglycerides are less than 400 mg/dL (4.5 mmol/L).

The Friedewald formula loses accuracy when triglycerides exceed 400 mg/dL, in patients with chylomicronemia, type III hyperlipoproteinemia, or when LDL is very low (< 50 mg/dL). In these cases, direct LDL measurement or alternate formulas are preferred.

The Martin-Hopkins (or Sampson) formula uses a flexible factor for VLDL calculation based on triglyceride and non-HDL cholesterol levels. It provides more accurate LDL estimates across a wider range of triglyceride values, including up to 800 mg/dL.

Non-HDL cholesterol = Total Cholesterol – HDL. It represents all atherogenic lipoproteins including LDL, VLDL, IDL, and Lp(a). Some guidelines prefer non-HDL over LDL because it does not require fasting and captures more lipid-related risk.

The total cholesterol-to-HDL ratio (TC/HDL) is a predictor of cardiovascular risk. A lower ratio is better. Ideal is < 3.5, average is 3.5–5.0, and > 5.0 indicates increased risk. It does not require calculation of LDL.

Very-low-density lipoprotein (VLDL) carries triglycerides from the liver to peripheral tissues. In the Friedewald formula, VLDL is estimated as Triglycerides / 5 (in mg/dL). Elevated VLDL is associated with increased CVD risk, especially when combined with high triglycerides.

Optimal LDL is < 100 mg/dL (< 2.6 mmol/L). Near optimal is 100–129 mg/dL. Borderline high is 130–159 mg/dL. High is 160–189 mg/dL. Very high is ≥ 190 mg/dL (≥ 4.9 mmol/L).

For most patients with diabetes, the LDL target is < 100 mg/dL (< 2.6 mmol/L). For those with diabetes and additional risk factors (overt ASCVD, CKD), the target is < 70 mg/dL (< 1.8 mmol/L).

For patients with established atherosclerotic cardiovascular disease (ASCVD), the LDL target is < 70 mg/dL (< 1.8 mmol/L) or a ≥ 50% reduction from baseline. For very high risk (recent ACS, polyvascular disease), consider < 55 mg/dL.

Moderate-intensity statins (atorvastatin 10–20 mg, rosuvastatin 5–10 mg) lower LDL by 30–50%. High-intensity statins (atorvastatin 40–80 mg, rosuvastatin 20–40 mg) lower LDL by ≥ 50%. Combination therapy with ezetimibe adds 15–20% reduction.

FH is a genetic disorder characterized by very high LDL levels from birth. Heterozygous FH presents with LDL 190–400 mg/dL. Homozygous FH presents with LDL > 500 mg/dL. Both require aggressive lipid-lowering therapy starting early in life.

Direct LDL measurement uses ultracentrifugation, electrophoresis, or homogeneous assays. Calculated LDL (Friedewald, Martin-Hopkins) estimates LDL from standard lipid panel. Direct measurement is preferred when triglycerides are high or non-fasting samples are used.

Dietary saturated fats and trans fats raise LDL. Replacing them with unsaturated fats (olive oil, nuts, avocados) and increasing soluble fiber (oats, beans, psyllium) can lower LDL by 5–15%. Plant sterols and stanols (2 g/day) can further reduce LDL by 5–10%.

Current guidelines (ACC/AHA) do not routinely require fasting for standard lipid panels. Non-HDL and TC/HDL ratio are reliable without fasting. However, triglycerides can be elevated postprandially, so LDL calculation may be less accurate in non-fasting samples.

Lp(a) is a modified LDL particle with an extra apo(a) protein. It is an independent risk factor for ASCVD and aortic stenosis. Levels are genetically determined and not significantly affected by statins. Elevated Lp(a) is defined as > 50 mg/dL or > 125 nmol/L.

The 2018 ACC/AHA guideline recommends statin therapy based on ASCVD risk: (1) Clinical ASCVD, (2) LDL ≥ 190 mg/dL, (3) Age 40–75 with diabetes, (4) Age 40–75 with 10-year ASCVD risk ≥ 7.5%. It emphasizes risk discussion and shared decision-making.

PCSK9 inhibitors (evolocumab, alirocumab) are injectable monoclonal antibodies that lower LDL by 50–60% by increasing LDL receptor recycling. They are used in FH, clinical ASCVD not at target, and statin-intolerant patients.

Ezetimibe inhibits intestinal cholesterol absorption at the NPC1L1 transporter. It lowers LDL by 15–20% and is used as add-on to statins or as monotherapy in statin-intolerant patients. The IMPROVE-IT trial showed CV benefit when added to simvastatin post-ACS.

Elevated triglycerides are an independent risk factor for CVD, especially when > 500 mg/dL (risk of pancreatitis). Management includes lifestyle modification (weight loss, exercise, low-carb diet), fibrates, marine omega-3 fatty acids (4 g/day), and icosapent ethyl.

Icosapent ethyl (Vascepa) is a highly purified EPA ethyl ester that reduces triglycerides and CV events. The REDUCE-IT trial demonstrated a 25% relative risk reduction in patients with elevated triglycerides and established CVD or diabetes on statin therapy.

Fibrates (fenofibrate, gemfibrozil) are PPAR-alpha agonists that primarily lower triglycerides by 30–50% and modestly raise HDL. Fenofibrate is preferred with statins (safer than gemfibrozil). Benefit is greatest in patients with high TG and low HDL.

Regular aerobic exercise (150 min/week of moderate-intensity) can lower LDL by 3–5 mg/dL, lower triglycerides by 5–10%, and raise HDL by 2–5 mg/dL. Resistance training also improves triglyceride and HDL levels.

HDL cholesterol is "good" cholesterol that removes excess cholesterol from peripheral tissues and delivers it to the liver for excretion (reverse cholesterol transport). Higher HDL is generally protective, but very high HDL (> 80 mg/dL) may be dysfunctional and not protective.

Metabolic syndrome is defined by 3 of 5 criteria: abdominal obesity (waist ≥ 40 in / 35 in), elevated triglycerides (≥ 150 mg/dL), low HDL (< 40/50 mg/dL), elevated BP (≥ 130/85), and elevated fasting glucose (≥ 100 mg/dL). It significantly increases CVD and diabetes risk.

LDL-C measures cholesterol mass within LDL particles. LDL-P (NMR-assessed) measures the number of LDL particles. Discordance (high LDL-P despite low LDL-C) may indicate higher residual risk, especially in patients with insulin resistance, diabetes, or hypertriglyceridemia.

Very low LDL levels (< 25 mg/dL) from aggressive lipid-lowering therapy have been associated with theoretical concerns about steroid hormone synthesis and vitamin D production. However, clinical trials have not shown significant adverse effects, and lower LDL is generally associated with lower CV risk.

APOE has three common alleles: E2, E3, E4. E2 is associated with type III hyperlipoproteinemia (high LDL and TG). E4 is associated with higher LDL and increased risk of Alzheimer’s. APOE genotyping can help in diagnosing dyslipidemia subtypes.

Sitosterolemia is a rare genetic disorder characterized by elevated plant sterols (sitosterol) due to ABCG5/ABCG8 mutations. It causes tendon xanthomas and premature ASCVD despite normal to moderately elevated LDL. Diagnosis requires plasma sterol analysis.

Menopause is associated with increased LDL and triglycerides and decreased HDL. Estrogen therapy may improve lipid profiles but is not recommended solely for CVD prevention. Lifestyle modification and pharmacotherapy as needed are the mainstays of management.