Small Dense Low-Density Lipoprotein Subfraction 4

sdLDL-4 is the smallest and most harmful form of LDL cholesterol, known for increasing the risk of heart disease.

📋 About This Biomarker

Small Dense LDL 4 (sdLDL-4) represents the smallest and most harmful type of LDL (“bad”) cholesterol particles found in the blood. While all LDL particles carry cholesterol to cells, the problem lies in how small and dense these particular particles are. sdLDL-4 is tiny enough to easily slip into artery walls, where it can become oxidised (damaged), causing inflammation and plaque build-up. Over time, this can lead to narrowed arteries, high blood pressure, heart attack, or stroke. These particles often show up in people with metabolic issues, such as type 2 diabetes, insulin resistance, obesity, and high triglycerides. Even if your total LDL looks normal, high sdLDL-4 can mean you're carrying a high hidden risk. It’s like looking beyond the big numbers to find out if the passengers in your bloodstream are the sneaky kind that cause the most damage.

🎯 Why We Test This

Testing sdLDL-4 helps uncover hidden cardiovascular risks that don’t appear on standard cholesterol tests. Even if your LDL or total cholesterol looks fine, having high sdLDL-4 means you're at higher risk for heart attacks and stroke. This test is especially important for people with diabetes, metabolic syndrome, or a strong family history of heart disease.

⚠️ What Affects It

sdLDL-4 levels can be increased by a diet high in sugar, refined carbohydrates, and ultra-processed foods. Lack of physical activity, overweight or obesity (especially around the belly), insulin resistance, and chronic inflammation all contribute. Genetics, low HDL (“good cholesterol”), smoking, alcohol, and menopause can also impact levels.

📈 How to Improve

To lower high or borderline sdLDL-4, cut back on sugary and processed foods, increase fibre-rich foods, include healthy fats like omega-3s, and aim for regular exercise (particularly cardio and strength training). Manage stress and stop smoking if applicable. If your level is low or near the low end, that’s fantastic - keep doing what works to maintain a low-risk cholesterol pattern.

📊 Understanding Your Results (mmol/L)

Low (< 0 mmol/L)
Low sdLDL-4 levels are excellent, showing that your blood cholesterol is mostly in a safer form. This usually reflects a healthy diet, regular exercise, and low inflammation. No action needed - just keep up your current habits!
Optimal (0 - 0.15 mmol/L)
A normal sdLDL-4 result means your body is producing relatively few of these dangerous small LDL particles, which is a positive sign for heart health. It suggests a healthier cholesterol pattern and better metabolic balance.
High (> 0.15 mmol/L)
High sdLDL-4 is a strong red flag. These small particles are considered highly atherogenic, meaning they’re strongly linked to artery damage and heart disease. If your sdLDL-4 is high, you're at increased risk for cardiovascular problems - even if your total cholesterol looks fine. Immediate action is often needed to reduce this risk.
Also known as: Small Dense LDL 4, sdLDL-4