LIPID PROFILE TESTING AND INTERPRETATION

CASE

A 59-year-old man living with type 2 diabetes for 11 years and no history of cardiovascular disease or kidney disease presents to clinic for an annual visit. He is currently taking atorvastatin 80 mg daily for lipid-lowering. The following laboratory results are obtained from a standard non-fasting lipid panel:

Total cholesterol: 123 mg/dL

Triglycerides: 145 mg/dL

HDL-C: 42 mg/dL

Non-HDL-C: 81 mg/dL

LDL-C: 65 mg/dL (calculated with the Samson equation)

INTRODUCTION

This Clinician Lighthouse navigates lipid profile testing and interpretation. The standard lipid panel is among the most frequently ordered laboratory tests and remains central to atherosclerotic cardiovascular disease (ASCVD) risk assessment. Accurate interpretation requires understanding of each component and its clinical relevance. Additional cholesterol tests, including apolipoprotein B (apoB) and Lipoprotein(a) (Lp[a]), are also guideline-recommended. This review outlines a systematic approach to ordering and interpreting the standard lipid panel, as well as apoB and Lp(a).

THE STANDARD LIPID PANEL

A standard lipid panel—which does not require fasting—includes total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL-C), and non-HDL-C, with calculation of low-density lipoprotein cholesterol (LDL-C). In adults >19 years, lipid panels are recommended at least every 5 years for screening in the general population.

Total Cholesterol

Total cholesterol represents the mass-based concentration of cholesterol across all lipoproteins circulating in plasma. These include the atherosclerotic lipoproteins LDL, very low-density lipoproteins (VLDL), VLDL remnants (also termed intermediate density lipoproteins [IDL]), Lp(a), and other, non-atherogenic lipoproteins (i.e. HDL-C and chylomicron remnants). Because total cholesterol does not distinguish between atherogenic and non-atherogenic lipoprotein cholesterol, it has limited clinical utility, though can be used to screen for familial hypercholesterolemia (see Table 1).²

Table 1:

Clinically Relevant Lipid Thresholds

Total Cholesterol	Included in scoring systems for Familial Hypercholesterolemia Simon Broome >260 mg/dL in children or >290 mg/dL in adults included in risk score MEDPED: (General population criteria for FH) ≥270 mg/dL if <20 years old ≥290 mg/dL if 20-39 years old ≥340 mg/dL if 30-39 years old ≥360 mg/dL if ≥40 years old   Thresholds are lower if known family history of FH
Triglycerides	≥150 mg/dL: Increased ASCVD risk. Risk enhancer to consider therapy if borderline-to-intermediate 10-year ASCVD risk. Icosapent ethyl may lower ASCVD risk if prior ASCVD or high-risk diabetes* if TG elevated on maximally tolerated statin. ≥500 mg/dL: Severe HTG. Treatment (fibrates, omega 3 fatty acid) indicated to lower risk of pancreatitis. Evaluate secondary causes. ≥1000 mg/dL: Extreme HTG. Highest pancreatitis risk. If familial chylomicron syndrome (FCS), treatment with olezarsen or plozasiran14
LDL-C	≥190 mg/dL: Statin recommended regardless of risk. Evaluate for possible familial hypercholesterolemia.
Lp(a)	≥125 nmol/L(~80th percentile): 1.4x increased ASCVD risk- risk enhancer. ≥250 nmol/L(~95th percentile): 2x increased ASCVD risk ≥350 nmol/L: 3x increased ASCVD risk ≥430 nmol/L (~99th percentile): 4x increased ASCVD risk; similar to HeFH

Percentiles and thresholds are adapted from the 2026 ACC/AHA Dyslipidemia Guideline.¹ Values shown for total cholesterol, TG, and LDL-C are in mg/dL. To convert to SI units, divide total cholesterol and LDL-C 38.6; for TG, divide by 88.6.

^*High-risk features include age ≥55 years for men or ≥65 years for women, current smoker, hypertension, high-density lipoprotein-cholesterol ≤40 mg/dL for men or ≤50 mg/dL for women, high-sensitivity C-reactive protein >3.0 mg/L, creatinine clearance >30 and <60 mL/ min, retinopathy; albuminuria (≥30 μg of albumin/mg creatinine), and ankle-brachial index <0.9.

ASCVD indicates atherosclerotic cardiovascular disease; FCS, familial chylomicronemia syndrome; FH, familial hypercholesterolemia; HeFH, heterozygous familial hypercholesterolemia; HTG, hypertriglyceridemia; LDL-C, low-density lipoprotein cholesterol; Lp(a), lipoprotein(a); MEDPED, Make Early Diagnosis to Prevent Early Deaths; and TG, triglycerides.

Triglycerides

A triglyceride measurement reflects the concentration of triglycerides in the plasma, the majority of which are carried on VLDL particles. After a meal, triglyceride levels increase due to the presence of chylomicrons; peaking 3-4 hours postprandially and returning to baseline by ~ 8 hours in healthy individuals.³ Fasting is not required for lipid panel measurement, though non-fasting patients with elevated triglycerides ≥400 mg/dL (≥4.5 mmol/L) mg/dL should have a fasting lipid panel repeated.

Elevated triglycerides (150-499 mg/dL, 1.7-5.6 mmol/L) are associated with increased ASCVD risk and is therefore considered a “risk-enhancer” to support lipid lowering therapy initiation in individuals at intermediate risk.¹ Secondary causes of hypertriglyceridemia (e.g., obesity, uncontrolled diabetes, alcohol use, hypothyroidism) should also be assessed.¹ Individuals with ASCVD or high-risk diabetes and persistently elevated triglycerides on maximally tolerated statin therapy may benefit from icosapent ethyl (Table 1).¹

In severe hypertriglyceridemia (triglycerides ≥500 mg/dL [5.7 mmol/L]) and particularly extreme hypertriglyceridemia (≥1000 mg/dL (11.3 mmol/L), short-term priority shifts to preventing acute pancreatitis. Management includes addressing secondary causes and dietary interventions to eliminate alcohol and reduce or eliminate added sugar, refined carbohydrates, saturated and total fat, and initiation of triglyceride-lowering therapy (e.g., fibrates or prescription omega-3 fatty acids) if dietary interventions are insufficient. Treatment-resistant extreme hypertriglyceridemia may be due to familial chylomicronemia syndrome (FCS) and should prompt specialist evaluation for potential therapy (plozasiran or olezarsan).

High-Density Lipoprotein Cholesterol

HDL-C represents the cholesterol content in HDL particles. Exercise and alcohol increase HDL-C, while obesity, metabolic syndrome, and diabetes are associated with lower HDL-C. Although low levels (<40 mg/dL [1.4 mmol/L] in men, <50 mg/dL [1.3 mmol/L] in women) are associated with increased ASCVD risk, clinical trials of HDL-raising therapies have generally failed to demonstrate ASCVD risk reduction.⁴ Therefore, HDL-C should be interpreted as a marker of risk rather than a modifiable target.

Non-High-Density Lipoprotein Cholesterol

Non-HDL-C is calculated by subtracting the HDL-C from the total cholesterol and represents the cholesterol content of all apoB-containing, atherogenic lipoproteins, including LDL, VLDL, remnants, and Lp(a). Non-HDL-C measurement is unaffected by fasting status.

Non-HDL-C is a stronger predictor of ASCVD than LDL-C, particularly in statin-treated patients, and is thus included in the PREVENT-ASCVD equations.⁵ In most individuals, non-HDL-C is approximately 30 mg/dL higher than LDL-C. A larger difference suggests an increased burden of triglyceride-rich remnant particles, commonly seen in obesity, diabetes, and hypertriglyceridemia. The 2026 ACC/AHA Dyslipidemia Guideline recommends treatment goals for both LDL-C and non-HDL-C (Table 2).¹

Table 2:

2026 ACC/AHA Dyslipidemia Guideline Treatment Targets¹

Treatment Group	LDL-C	Non- HDL-C	ApoB
PREVENT-ASCVD Risk Low 10-year ASCVD risk (<3%) with LDL-C ≥160 mg/dL or 30-year risk ≥10% Borderline-to-intermediate 10-year ASCVD risk (3 to <10%) Comorbidity-specific Diabetes age 40-75 years without ASCVD or diabetes-specific risk enhancers* Imaging CAC 1-99 AU and <75th percentile for age, sex, and race Mild CAC on nongated CT	<100 mg/dL	<130 mg/dL	<90 mg/dL
PREVENT-ASCVD Risk High 10-year ASCVD risk (10%) Comorbidity-specific FH without ASCVD Diabetes age 40-75 years without ASCVD but with diabetes-specific risk enhancers* Imaging CAC 100-999 AU or ≥75th percentile for age, sex, and race Established ASCVD ASCVD not at very high risk	<70 mg/dL	<100 mg/dL	<70 mg/dL
Imaging CAC ≥1000 AU (optional if CAC 300-999 AU) Established ASCVD ASCVD at very high risk† (optional if ASCVD not at very high risk) ASCVD + FH	<55 mg/dL	<85 mg/dL	<55 mg/dL

Treatment targets shown for LDL-C and non-HDL-C are in mg/dL; to convert to SI units, divide by 38.6.

^*Diabetes-specific risk-enhancers include long duration of diabetes (≥10 years for type 2 diabetes, ≥20 years for type 1 diabetes), albuminuria (≥30 μg of albumin/mg creatinine), eGFR <60 mL/min/1.73m², retinopathy, neuropathy, and ankle-brachial index <0.9.

^†Very high risk is defined as ≥2 major ASCVD events or 1 major ASCVD event and ≥2 high-risk conditions (age ≥65 years, coronary revascularization, current smoker, diabetes, heart failure, hypertension, LDL-C ≥100 mg/dL despite maximally tolerated statin and ezetimibe.

ASCVD indicates atherosclerotic cardiovascular disease; ApoB, apolipoprotein B; AU, Agatston units; CAC, coronary artery calcium; CKD, chronic kidney disease; CT, computed tomography; eGFR, estimated glomerular filtration rate; FH, familial hypercholesterolemia; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol; non–HDL-C, non–high-density lipoprotein cholesterol; and PREVENT, Predicting Risk of Cardiovascular Disease EVENTs.

Low-Density Lipoprotein Cholesterol Calculation

LDL-C reflects the cholesterol content within LDL particles. As the main endpoint for most lipid lowering clinical trials, LDL-C remains the primary target for lipid-lowering therapy. LDL-C is not directly measured in the standard lipid panel, but is estimated using an equation based on measured HDL-C, triglycerides, and total cholesterol. Either the Martin-Hopkins or the Sampson formula should be used; the older Friedewald equation is less accurate.¹ All LDL-C-estimating equations have limitations at very low LDL-C levels. While direct LDL-C assays can be used to isolate LDL particles, results are variable and generally no more accurate than calculated estimates.⁶ LDL-C levels above 190 mg/dL should prompt evaluation for secondary causes and familial hypercholesterolemia (Table 1). LDL-C goals for lipid-lowering range from <55 mg/dL to <100 mg/dL depending on risk of ASCVD events (Table 2).

Lipid Ratios

Although current guidelines do not use lipid ratios to guide therapy or risk assessment, some lipid reports contain them nevertheless. Higher triglyceride-to-HDL-C ratios have been associated with insulin resistance and an atherogenic metabolic phenotypes.{Quispe, 2015 #8} Higher total cholesterol:HDL-C ratios are associated with reduced ASCVD risk, but does not eliminate the risk of elevated LDL-C or non-HDL-C {Arsenault, 2009 #15} Treatment decisions should be based on individual lipid components parameters (e.g., LDL-C), regardless of the ratio.

BEYOND THE STANDARD LIPID PANEL

Apolipoprotein B

Every atherogenic lipoprotein (LDL, VLDL, remnants, and Lp[a]) has a single apoB protein. Chylomicrons also contain apoB but contribute minimally to circulating apoB levels, even in the postprandial state. Whereas LDL-C and non-HDL-C quantify the mass concentration of cholesterol within lipoproteins, apoB reflects the total number of circulating atherogenic particles. ApoB is more strongly associated with ASCVD risk than LDL-C or non-HDL-C.⁹

In most individuals, LDL-C, non-HDL-C, and apoB are directionally (i.e. high vs low) concordant. However, discordance can occur, with normal LDL-C or non-HDL-C but elevated apoB, indicating increased atherogenic particle burden and ASCVD risk.¹⁰ Discordance is more common in (but not exclusive to) individuals with hypertriglyceridemia, cardio-kidney-metabolic syndrome, or diabetes.¹⁰ In these individuals, apoB measurement is recommended to refine risk assessment.¹

Guidelines also recommend measurement of apoB in individuals on lipid-lowering therapy once LDL-C and non-HDL-C goals are met (Table 2). If apoB is above target, therapy should be intensified.

Lipoprotein(a)

Lp(a) is composed of an LDL-like particle with an apolipoprotein(a) covalently bound to apoB. Elevated Lp(a) is associated with an increased risk of ASCVD and calcific aortic stenosis. Lp(a) levels are approximately 90% genetically determined, remain stable across the lifespan, and follow a pattern of autosomal dominant inheritance.¹¹

Because Lp(a) particles contain cholesterol within an LDL-like particle, they contribute to measured LDL-C. However, LDL particles are far more numerous, so in most individuals, the proportion of LDL-C from Lp(a) particles is low [average ~3%, ~15% in those with high Lp(a)].¹²

Every individual should undergo Lp(a) testing at least once in their lifetime.¹ Given its genetic determination and stability, repeat testing is usually unnecessary. If elevated, cascade screening of first-degree relatives should be performed, as ~50% will also have a high Lp(a). Lp(a) should be measured using a validated molar (nmol/L) assay, which are preferred over mass-based assays for accuracy.¹ While Lp(a)-lowering therapies remain under investigation,¹³ management currently focuses on intensifying LDL-C lowering and lifestyle measures to reduce global ASCVD risk.

“Advanced” lipid testing

Nuclear magnetic resonance (NMR) spectroscopy can be used to measure the number and size of lipoprotein particles. However, prospective studies have not demonstrated meaningful improvement in risk reclassification when NMR-derived measurements are added to standard lipid parameters. As a result, the current Guidelines recommend against NMR and other forms of “advanced lipoprotein testing” beyond the traditional lipid panel, apoB, and Lp(a).¹

CASE FOLLOW-UP

The patient’s duration of diabetes places him at higher risk with an LDL-C target of <70 mg/dL (Table 2). Having met this goal, the patient undergoes additional testing for apoB to assess residual atherogenic burden, as well as Lp(a) for further risk stratification, since his has never been checked previously. His apoB level is 85 mg/dL—above the <70mg/dL goal for high-risk diabetes—supporting intensification of lipid-lowering therapy. His Lp(a) level is 221 nmol/L, which also independently elevates his ASCVD risk and warrants cascade screening of first-degree relatives. After lipid therapy is intensified, repeat lipid testing should be performed in 4-12 weeks to evaluate efficacy and then every 6-12 months for ongoing monitoring.