Metabolic syndrome (syndrome X): the 5 criteria, symptoms, and what your labs show

Metabolic syndrome (also called syndrome X or insulin resistance syndrome) is diagnosed by a count. When any 3 of 5 measures cross a cutoff, the combined risk of heart disease, stroke and type 2 diabetes rises more than any one of them suggests. ¹⁴ The five are a large waist, high triglycerides (a blood fat), low HDL cholesterol (the "good" cholesterol that carries fat away from arteries), blood pressure of 130/85 or higher, and a fasting blood sugar of 100 mg/dL or higher. ² Most of these cause no symptoms, which is why it so often shows up first on a routine fasting blood test rather than in how someone feels. What to do next: if your lab report flags triglycerides, HDL or fasting glucose, count how many of the five you meet using the table below, and bring that count, with your waist size and blood pressure, to your clinician.

What is metabolic syndrome (syndrome X)?

The NHLBI (National Heart, Lung, and Blood Institute) describes metabolic syndrome as “a group of conditions that together raise your risk of coronary heart disease, diabetes, stroke, and other serious health problems.” ⁴ The older name, syndrome X, comes from researchers noticing that high blood pressure, high triglycerides, low HDL and high blood sugar turned up together in the same people. The 2009 harmonized statement, agreed by the International Diabetes Federation, the NHLBI, the American Heart Association and three other bodies, calls it “a cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus, which occur together more often than by chance alone.” ¹

The thread connecting the five is usually insulin resistance: muscle, fat and liver cells respond poorly to insulin, the hormone that moves sugar out of the blood. The pancreas compensates by making more insulin, and that extra insulin, together with the fat stored around the organs in the belly, pushes the liver to make more triglycerides, lowers HDL and raises blood pressure. ⁵ Blood sugar is often the last of the five to climb, because the extra insulin holds it down for years.

The reason the count matters is that the risks stack. Pooling 87 studies, a 2010 meta-analysis in the Journal of the American College of Cardiology found that metabolic syndrome was linked to about 2.35 times the risk of cardiovascular disease, 2.4 times the risk of cardiovascular death, 2.27 times the risk of stroke and 1.58 times the risk of death from any cause. ⁹ People with metabolic syndrome who did not have diabetes still carried a high cardiovascular risk. ⁹

What are the 5 criteria for metabolic syndrome?

Before 2009, groups disagreed about whether a large waist had to be present. The harmonized definition settled it: no single criterion is required, any three of five qualify, and one set of blood cutoffs applies to everyone, while waist cutoffs can follow national or regional standards. ¹ The US cutoffs below are the ones MedlinePlus and the NHLBI use. ²³

Two details trip people up. First, the medicine rule: a person whose triglycerides read 120 on a prescription that lowers them still meets the triglyceride criterion, because the medicine is masking the number. ³ Second, waist cutoffs depend on ancestry. People of Asian ancestry develop insulin resistance and type 2 diabetes at smaller waist sizes, so MedlinePlus lists 35 inches for men and 30 inches for women. ³ The NHLBI notes that clinicians may use different waist values depending on race and ethnicity. ⁴

A worked example: counting the criteria

Take a 52-year-old man whose fasting lipid panel shows triglycerides of 180 mg/dL and HDL of 38 mg/dL, with a fasting glucose of 104 mg/dL. His blood pressure at the visit is 126/82 and nobody has measured his waist. From the blood test alone he meets three criteria: triglycerides (180 is above 150), HDL (38 is below 40 for a man) and fasting glucose (104 is above 100). That is enough for metabolic syndrome under the harmonized definition, before the tape measure or the blood pressure cuff come into it. ¹² His clinician would confirm the numbers, check his waist and blood pressure again, and look at the full picture, including his LDL cholesterol, smoking and family history.

Who gets metabolic syndrome, and why

The NHLBI names overweight and obesity as the main risk factors, with risk rising with age. ⁵ Other risk factors it lists are a family history of diabetes, inactivity, an eating pattern with large portions, poor sleep including sleep apnea, shift work, smoking and heavy drinking, and, in older adults, being a woman. ⁵ PCOS (polycystic ovary syndrome) raises the risk through the same insulin resistance, and some medicines used for allergies, bipolar disorder, depression, HIV and schizophrenia raise it too. ⁵ A normal weight does not rule it out: in US survey data, fewer than a third of normal-weight adults had every measure in the healthy range. ¹⁰

Metabolic health vs metabolic syndrome

Searches for “what is metabolic health” have grown alongside searches for metabolic syndrome, and the two sit far apart. Metabolic health usually means every one of the five measures is in its optimal range without medicine. Using recent guideline cutoffs, Araujo and colleagues at the University of North Carolina found in national survey data from 2009 to 2016 that only 12.2% of US adults met that bar. ¹⁰ Fewer than a third of normal-weight adults were metabolically healthy, and the share fell to 8.0% among adults with overweight and 0.5% among adults with obesity. ¹⁰

The blood tests and markers to check

Three of the five criteria are blood tests, and a handful of add-on markers help explain why the numbers are off and how much risk they carry. If you want a refresher on the lipid results first, LifeFrom's guide on how to read your lipid panel walks through each line, and blood sugar explained covers fasting glucose and A1C.

Your lipid panel already holds the numbers for two ratios that track insulin resistance and heart risk. The tool below turns total cholesterol, HDL and triglycerides into those ratios, and the cholesterol ratio calculator does the same with a fuller explanation.

Interactive

Your cholesterol ratios, in context

Two ratios that say more than any single number. Nothing leaves your browser.

Total cholesterolmg/dLHDL-Cmg/dLTriglyceridesmg/dL

Enter all three numbers to see your ratios.

Educational, not a diagnosis. TG/HDL thresholds are population-dependent and a surrogate for insulin resistance, not a diagnosis of it. Bands describe the values, not you.

Have your own numbers?Add your result. LifeFrom reads it free.Add the lab results you already have, and LifeFrom reads each marker next to the others it moves with, in plain language, with the sources it used. Free, on the web or in the app.Start on the web

How the markers read together

Triglycerides 150, HDL 40 or 50, glucose 100: what the numbers mean

Each metabolic syndrome cutoff is a line drawn on a sliding scale of risk. A triglyceride level of 150 mg/dL counts toward the syndrome, but a level of 148 does not mean all is well, and triglycerides rise after a big meal or a few drinks, so the criterion uses a fasting level and a high nonfasting result is often repeated fasting. ³ HDL uses different lines by sex: below 40 mg/dL counts for men and below 50 mg/dL for women. ² A fasting glucose of 100 mg/dL is both the metabolic syndrome cutoff and the start of the prediabetes range; 126 mg/dL or higher on two tests is the diabetes range. ⁷ Blood pressure counts at 130 systolic (top number) or 85 diastolic (bottom number), whichever comes first. ²

If your HOMA-IR or fasting insulin is high but you meet fewer than three criteria, that is insulin resistance without the full syndrome, and LifeFrom's HOMA-IR calculator shows how the score is built from your fasting insulin and glucose. The inflammation markers guide explains why hs-CRP is read with the rest of your heart risk rather than on its own.

Conditions that overlap with or look like metabolic syndrome

Several conditions share parts of the picture, and some can cause it. The test in the right column is what usually tells them apart.

A newer label also turns up in searches: cardiovascular-kidney-metabolic (CKM) syndrome. A 2023 American Heart Association presidential advisory describes it as reflecting “the interplay among metabolic risk factors, chronic kidney disease, and the cardiovascular system,” and stages it from early risk to established disease. ¹³ In practice it adds kidney tests to the picture metabolic syndrome starts, so people with metabolic syndrome are often also checked for chronic kidney disease.

What can help metabolic syndrome, with the evidence

Lifestyle change is first-line because it is the one approach that moves all five numbers at once. ⁶ In a 2012 meta-analysis of randomized trials, lifestyle programs roughly doubled the share of people whose metabolic syndrome resolved within a year compared with usual care, and lowered systolic blood pressure by about 6 mmHg, triglycerides by about 12 mg/dL, waist by about 2.7 cm and fasting glucose by about 11 mg/dL; HDL did not change significantly. ¹¹ When medicine is needed, there is no single drug for metabolic syndrome. A clinician treats the part that needs it, which is why each row below carries its own evidence.

Medicines are named here as facts about how the condition is managed, not as a suggestion for you. Whether any of them fits is a decision for the clinician who knows your history, and the compound guides for metformin, statins and omega-3 explain how each works and what to watch.

Monitoring and retesting

Because the criteria are numbers, progress shows up as numbers. Waist and blood pressure can be checked at home; the blood markers need a lab. LifeFrom's guide on why trends beat single readings explains why two or three results in a row tell you more than one.

When to see a doctor

For everything else, metabolic syndrome is a reason for a planned appointment. Bring your latest lipid panel, glucose and A1C, home blood pressure readings and a waist measurement.

Questions to ask your clinician

• How many of the five criteria do I meet, counting any medicines I take?
• Which of my numbers is furthest from the cutoff, and which should we work on first?
• Should we add fasting insulin, apoB or hs-CRP to understand my risk better?
• Is my ALT high enough to look for fatty liver?
• What is my 10-year heart risk, and does it change whether a statin makes sense?
• What weight change and activity target is realistic for me?
• When should we recheck my labs, and which ones?

If heart risk is your main worry, LifeFrom's heart page gathers the cholesterol and blood pressure markers in one place.

This guide is general education, not medical advice or a diagnosis. The clinician who knows your history reads your results and makes decisions with you.