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Biomarker Reference
Interactive Reference Tool
The Longevity
Biomarker Guide
What each common marker measures, how it is read against clinical guidelines and reference ranges, and what results can mean. Every entry links to its sources, and markers without an agreed cut-off say so.
42
Biomarkers
7
Categories
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Entries Cited
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Cardiovascular & Lipid Markers
7ApoB
Apolipoprotein B
How it's read
No single cut-off; read it with your overall cardiovascular risk
ApoB counts atherogenic particles: each LDL, VLDL and Lp(a) particle carries one ApoB molecule. It can capture cardiovascular risk that LDL cholesterol misses when the two disagree.
How it's read
No single cut-off; read it with your overall cardiovascular risk
Measured in: mg/dL
What results can mean
A higher ApoB means more particles that can enter artery walls. Your clinician can weigh it alongside LDL cholesterol and your other risk factors.
What reliably changes it
StatinsEzetimibePCSK9 inhibitors
Sources: ApoB review · 2026 ACC/AHA dyslipidemia guideline
📖 ApoB: The Cholesterol Number Your Doctor Probably Is Not Ordering
Lp(a)
Lipoprotein(a)
How it's read
Measure at least once in adulthood. 50 mg/dL (125 nmol/L) or more is a risk-enhancing factor in the 2026 US dyslipidemia guideline
A cholesterol-carrying particle whose level is largely inherited and changes little with lifestyle. Genetic and epidemiological studies show that it causes cardiovascular disease, with risk rising continuously as levels rise.
How it's read
Measure at least once in adulthood. 50 mg/dL (125 nmol/L) or more is a risk-enhancing factor in the 2026 US dyslipidemia guideline
Measured in: mg/dL or nmol/L (not interchangeable)
What results can mean
A high Lp(a) adds to your cardiovascular risk even when LDL cholesterol is low, which is a reason to manage your other risk factors closely. Drugs that lower Lp(a) are being tested in outcome trials.
LDL Cholesterol
LDL-C
How it's read
Goals depend on risk: under 100 mg/dL at borderline or intermediate 10-year risk, under 70 mg/dL at high risk (2026 US guideline)
LDL cholesterol is the main target of cholesterol treatment. US guidelines base treatment decisions on your overall cardiovascular risk.
How it's read
Goals depend on risk: under 100 mg/dL at borderline or intermediate 10-year risk, under 70 mg/dL at high risk (2026 US guideline)
Measured in: mg/dL
What results can mean
Above 100 mg/dL, what the number means depends on your age, blood pressure, diabetes, smoking and family history.
What reliably changes it
StatinsEzetimibePCSK9 inhibitors
Triglycerides
TG (fasting)
How it's read
Normal under 150 mg/dL · borderline 150–199 · high 200+ · very high 500+ mg/dL
Fats carried in the blood that reflect diet, weight, alcohol and metabolic health.
How it's read
Normal under 150 mg/dL · borderline 150–199 · high 200+ · very high 500+ mg/dL
Measured in: mg/dL
What results can mean
High levels raise cardiovascular risk, and very high levels (500 mg/dL or more) can cause pancreatitis.
What reliably changes it
Weight lossLess alcoholLess added sugar
HDL Cholesterol
HDL-C
How it's read
Low under 40 mg/dL (men) or 50 mg/dL (women) · best 60 mg/dL or more
HDL carries cholesterol away from the arteries; low levels are linked to higher cardiovascular risk.
How it's read
Low under 40 mg/dL (men) or 50 mg/dL (women) · best 60 mg/dL or more
Measured in: mg/dL
What results can mean
Smoking lowers HDL cholesterol.
What reliably changes it
Not smoking
Sources: MedlinePlus: Cholesterol levels
📖 ApoB: The Cholesterol Number Your Doctor Probably Is Not Ordering
CAC Score
Coronary artery calcium
How it's read
0 means no detectable calcified plaque; higher scores (in Agatston units) mean more plaque
A CT scan that measures calcified plaque in the arteries of the heart.
How it's read
0 means no detectable calcified plaque; higher scores (in Agatston units) mean more plaque
Measured in: Agatston units
What results can mean
In a large US cohort followed for 10 years, people with a score of 0 had low rates of heart attacks and strokes, and rates rose steadily with higher scores, being highest above 300.
Sources: MESA 10-year study (Budoff 2018)
📖 Coronary Artery Calcium Scoring: What Your Score Means and When It Is Used
Blood Pressure
Systolic / diastolic
How it's read
Normal under 120/80 mmHg · elevated 120–129 and under 80 · stage 1: 130–139 or 80–89 · stage 2: 140+ or 90+ mmHg
High blood pressure makes the heart work harder and over time raises the risk of heart attack, stroke, heart failure and kidney failure.
How it's read
Normal under 120/80 mmHg · elevated 120–129 and under 80 · stage 1: 130–139 or 80–89 · stage 2: 140+ or 90+ mmHg
Measured in: mmHg
What results can mean
Categories are based on readings taken over time rather than a single measurement. Above 180/120, seek medical care right away.
Sources: MedlinePlus: High blood pressure
Metabolic Markers
9Fasting Insulin
Serum insulin, fasting
How it's read
No agreed cut-off; labs and assays differ
Fasting insulin rises as insulin resistance develops, but assays differ between labs and there is no agreed diagnostic cut-off. It is most useful alongside fasting glucose and tracked over time.
How it's read
No agreed cut-off; labs and assays differ
Measured in: µIU/mL
What results can mean
Most useful alongside fasting glucose (as HOMA-IR) and tracked over time.
Sources: HOMA-IR cut-offs vary · Whitehall II trajectories
📖 Fasting Insulin and HOMA-IR: The Biomarkers That Catch Metabolic Disease Decades Early
HOMA-IR
Insulin × glucose (mg/dL) ÷ 405
How it's read
No universal cut-off
HOMA-IR estimates insulin resistance from fasting insulin and glucose. Thresholds used in studies vary with age, sex and population, so there is no universal cut-off.
How it's read
No universal cut-off
Measured in: index (no unit)
What results can mean
Compare your own results over time rather than against a single threshold.
Sources: HOMA-IR cut-offs vary
📖 Fasting Insulin and HOMA-IR: The Biomarkers That Catch Metabolic Disease Decades Early
HbA1c
Glycated hemoglobin
How it's read
Normal under 5.7% · prediabetes 5.7–6.4% · diabetes 6.5% or higher
A measure of average blood sugar over the previous two to three months.
How it's read
Normal under 5.7% · prediabetes 5.7–6.4% · diabetes 6.5% or higher
Measured in: %
What results can mean
A diagnosis of diabetes requires two abnormal results. For many people who have diabetes, the treatment goal is below 7%.
Sources: MedlinePlus: HbA1c test · MedlinePlus: A1C test
📖 Continuous Glucose Monitoring for Non-Diabetics: What Your Blood Sugar Does All Day
Fasting Glucose
Fasting plasma glucose
How it's read
Normal under 100 mg/dL · prediabetes 100–125 mg/dL · diabetes 126 mg/dL or higher
Blood sugar measured after at least eight hours without food.
How it's read
Normal under 100 mg/dL · prediabetes 100–125 mg/dL · diabetes 126 mg/dL or higher
Measured in: mg/dL
What results can mean
A result in the diabetes range needs to be confirmed with a repeat test.
Sources: MedlinePlus: Prediabetes
📖 Continuous Glucose Monitoring for Non-Diabetics: What Your Blood Sugar Does All Day
Uric Acid
Serum urate
How it's read
Gout treatment target under 6 mg/dL
The end product of purine breakdown. High levels cause gout and kidney stones.
How it's read
Gout treatment target under 6 mg/dL
Measured in: mg/dL
What results can mean
High uric acid is associated with high blood pressure and kidney disease, but in two trials, lowering it with allopurinol did not slow kidney function decline.
Ferritin
Serum ferritin (iron stores)
How it's read
Used to diagnose iron deficiency; with infection or inflammation, below 70 ng/mL may indicate deficiency in adults; above 150 ng/mL (menstruating women) or 200 ng/mL (men and other women) may indicate a risk of iron overload
Ferritin reflects the body's iron stores.
How it's read
Used to diagnose iron deficiency; with infection or inflammation, below 70 ng/mL may indicate deficiency in adults; above 150 ng/mL (menstruating women) or 200 ng/mL (men and other women) may indicate a risk of iron overload
Measured in: ng/mL (same as µg/L)
What results can mean
Ferritin also rises with inflammation, infection and liver disease, so a normal or high level does not rule out iron deficiency when inflammation is present.
Sources: WHO 2020 ferritin guideline
📖 Air Quality and Longevity: The Invisible Environmental Factor Shortening Your Life
eGFR
Estimated glomerular filtration rate
How it's read
Below 60 mL/min/1.73 m² for 3 months or more indicates chronic kidney disease
An estimate of kidney function calculated from blood creatinine (and sometimes cystatin C), age and sex.
How it's read
Below 60 mL/min/1.73 m² for 3 months or more indicates chronic kidney disease
Measured in: mL/min/1.73 m²
What results can mean
A single low result should be repeated; kidney damage can also show up as albumin in the urine.
Sources: KDIGO definition of CKD
📖 Kidney Health and Longevity: The Organ That Predicts Your Cardiovascular Future
ALT
Alanine aminotransferase
How it's read
Healthy ALT range up to 33 U/L (men) and 25 U/L (women)
A liver enzyme that leaks into the blood when liver cells are irritated or damaged.
How it's read
Healthy ALT range up to 33 U/L (men) and 25 U/L (women)
Measured in: U/L
What results can mean
Fatty liver, alcohol, medicines and recent muscle injury can all raise ALT; persistent elevation should be evaluated.
Sources: ACG liver chemistry guideline
📖 Liver Health and Longevity: Fatty Liver, How It Is Detected and What Helps
PSA
Prostate-specific antigen
How it's read
No single normal value; screening men aged 55 to 69 is an individual decision
A protein made by the prostate that can rise with prostate cancer, but also with benign enlargement and inflammation.
How it's read
No single normal value; screening men aged 55 to 69 is an individual decision
Measured in: ng/mL
What results can mean
PSA screening may prevent about 1.3 prostate cancer deaths per 1,000 men aged 55 to 69 over about 13 years, but false positives and overdiagnosis are common, so the US Preventive Services Task Force recommends an individual decision.
Sources: USPSTF 2018 recommendation
📖 Longevity for Men: The Male-Specific Aging Timeline and What to Do About It
Inflammatory Markers
3hsCRP
High-sensitivity C-reactive protein
How it's read
Under 1 mg/L lower risk · 1–3 mg/L average · over 3 mg/L higher; over 10 mg/L suggests acute inflammation
A liver protein that rises with inflammation. The high-sensitivity test is used to refine cardiovascular risk.
How it's read
Under 1 mg/L lower risk · 1–3 mg/L average · over 3 mg/L higher; over 10 mg/L suggests acute inflammation
Measured in: mg/L
What results can mean
Infections, injuries and other inflammation raise CRP, so a high result should be repeated when you are well.
Homocysteine
Total plasma homocysteine
How it's read
Elevated above 15 µmol/L
An amino acid that rises when vitamin B12 or folate is low.
How it's read
Elevated above 15 µmol/L
Measured in: µmol/L
What results can mean
B vitamins lower homocysteine, but trials found that lowering it did not prevent heart attacks.
IL-6
Interleukin-6
How it's read
No agreed clinical range; mainly a research marker
A signalling protein that drives inflammation; chronic low-grade inflammation tends to rise with age ("inflammaging").
How it's read
No agreed clinical range; mainly a research marker
Measured in: pg/mL
What results can mean
IL-6 is not used to guide routine care.
Hormonal Markers
8TSH
Thyroid-stimulating hormone
How it's read
Usual range about 0.4–4.8 mIU/L (labs vary)
A pituitary hormone that tells the thyroid to make hormone; it is the main screening test for thyroid function.
How it's read
Usual range about 0.4–4.8 mIU/L (labs vary)
Measured in: mIU/L
What results can mean
A mildly raised TSH with normal free T4 is subclinical hypothyroidism; in adults 65 and over, levothyroxine did not improve symptoms in the TRUST trial.
Free T3
Free triiodothyronine
How it's read
Reference ranges vary by lab; usually read alongside TSH and free T4
T3 is the most active thyroid hormone; most of it is made from T4 in the body's tissues.
How it's read
Reference ranges vary by lab; usually read alongside TSH and free T4
Measured in: pg/mL
What results can mean
Thyroid status is judged mainly from TSH and free T4.
Sources: Subclinical hypothyroidism review
📖 Longevity Protocol with Thyroid Disorders: Hashimoto's, Graves', and Hypothyroidism
Total Testosterone (men)
Serum testosterone, morning
How it's read
Harmonized range for men 264–916 ng/dL
The main male sex hormone; levels fall gradually with age.
How it's read
Harmonized range for men 264–916 ng/dL
Measured in: ng/dL
What results can mean
Guidelines diagnose low testosterone only when there are symptoms and repeated morning tests are low.
IGF-1
Insulin-like growth factor 1
How it's read
Age-specific reference ranges; no agreed target
A growth factor driven by growth hormone.
How it's read
Age-specific reference ranges; no agreed target
Measured in: ng/mL
What results can mean
Lower IGF-1 signalling is linked to longer life in animals, and in a study of 184 people in their 90s, women with IGF-1 at or below 96 ng/mL lived longer; the same was true for men and women with a history of cancer.
Sources: Milman 2014
📖 mTOR: The Master Growth Switch and What Turning It Down Does
DHEA-S
Dehydroepiandrosterone sulfate
How it's read
Age- and sex-specific reference ranges
An adrenal hormone.
How it's read
Age- and sex-specific reference ranges
Measured in: µg/dL
What results can mean
In a two-year trial in older adults, DHEA supplements did not improve fitness, muscle strength or insulin sensitivity.
Sources: Nair 2006 trial
📖 Hormones and Longevity: The Complete Guide to Your Body's Aging Signals
Estradiol (women)
Serum estradiol
How it's read
Varies with the menstrual cycle and after menopause; no target
The main estrogen before menopause; levels fall after menopause.
How it's read
Varies with the menstrual cycle and after menopause; no target
Measured in: pg/mL
What results can mean
Hormone therapy is judged on symptoms and risks rather than on a blood level; guidelines support it for hot flashes and preventing bone loss in women under 60 or within 10 years of menopause.
Sources: Menopause Society statement 2022
📖 HRT for Women: What the Evidence Shows About Hormone Therapy After Menopause
Cortisol
Serum cortisol, morning
How it's read
Reference ranges vary by lab and time of day
The main stress hormone, produced by the adrenal glands.
How it's read
Reference ranges vary by lab and time of day
Measured in: µg/dL
What results can mean
Blood cortisol is measured mainly to diagnose adrenal disorders, such as adrenal insufficiency, rather than to track stress.
SHBG
Sex hormone-binding globulin
How it's read
Varies by sex and age
A protein that binds testosterone and estradiol in the blood.
How it's read
Varies by sex and age
Measured in: nmol/L
What results can mean
When SHBG is altered, or total testosterone is near the lower limit, guidelines recommend measuring free testosterone.
Nutritional Biomarkers
7Vitamin D (25-OH)
25-hydroxyvitamin D
How it's read
Sufficient for most people at 20 ng/mL (50 nmol/L) or more · risk of deficiency rises below 12 ng/mL (30 nmol/L) · above 50 ng/mL (125 nmol/L) can be associated with adverse effects
The blood test for vitamin D status.
How it's read
Sufficient for most people at 20 ng/mL (50 nmol/L) or more · risk of deficiency rises below 12 ng/mL (30 nmol/L) · above 50 ng/mL (125 nmol/L) can be associated with adverse effects
Measured in: ng/mL (or nmol/L)
What results can mean
In the VITAL trial, vitamin D supplements did not reduce cancer or cardiovascular events in generally healthy adults, and the NIH notes possible adverse effects above 50 ng/mL.
Sources: NIH ODS: Vitamin D · VITAL trial
📖 Vitamin D and Longevity: Separating Genuine Benefit from Wishful Thinking
Omega-3 Index
EPA + DHA in red blood cells
How it's read
Omega-3 index under 4% highest-risk zone · 8% or more lowest-risk zone
The share of EPA and DHA in red blood cell membranes, reflecting omega-3 intake over recent months.
How it's read
Omega-3 index under 4% highest-risk zone · 8% or more lowest-risk zone
Measured in: % of red blood cell fatty acids
What results can mean
The index was proposed as a cardiovascular risk marker; the original analysis linked 8% or more to the lowest risk of death from coronary heart disease.
Sources: Omega-3 index (Harris 2004)
📖 Omega-3 Fatty Acids and Longevity: What Decades of Research Actually Prove
Magnesium
Serum magnesium
How it's read
Normal serum level 1.7–2.2 mg/dL (labs vary slightly)
Magnesium is needed by hundreds of enzymes. Only a small share of the body's magnesium is in the blood, so a normal serum level does not rule out low stores.
How it's read
Normal serum level 1.7–2.2 mg/dL (labs vary slightly)
Measured in: mg/dL
What results can mean
About half of US adults consume less than the estimated requirement.
Sources: MedlinePlus: Magnesium blood test · Rosanoff 2012
📖 Magnesium: The Deficient Mineral at the Center of 300+ Enzymatic Reactions
Vitamin B12
Serum cobalamin
How it's read
Subnormal under 200–250 pg/mL
Needed for nerves and red blood cells.
How it's read
Subnormal under 200–250 pg/mL
Measured in: pg/mL
What results can mean
With symptoms such as numbness or anemia and a level between 150 and 399 pg/mL, a methylmalonic acid (MMA) test can confirm deficiency.
Sources: NIH ODS: Vitamin B12
📖 Folate vs Folic Acid: MTHFR, Methylfolate and What the Evidence Shows
Folate
Serum or red-cell folate
How it's read
Adequate: serum folate above 3 ng/mL, or red-cell folate above 140 ng/mL
Folate is needed to make DNA and red blood cells; when it is low, homocysteine rises.
How it's read
Adequate: serum folate above 3 ng/mL, or red-cell folate above 140 ng/mL
Measured in: ng/mL
What results can mean
Most people in the US have adequate folate status.
Sources: NIH ODS: Folate
📖 Folate vs Folic Acid: MTHFR, Methylfolate and What the Evidence Shows
Zinc
Plasma zinc
How it's read
Reference ranges vary by lab
Zinc is essential for immune function, growth and wound healing.
How it's read
Reference ranges vary by lab
Measured in: µg/dL
What results can mean
Ask your clinician how to interpret your result against your lab's range.
Sources: Prasad 2013
📖 Zinc and Immune Aging: Why This Mineral Is Critical After 60
Selenium
Serum selenium
How it's read
Reference ranges vary by lab; no target
An essential trace mineral.
How it's read
Reference ranges vary by lab; no target
Measured in: µg/L
What results can mean
More is not better: in a randomized trial, long-term selenium supplements increased the risk of type 2 diabetes.
Sources: Stranges 2007 trial
Fitness & Performance Markers
4VO₂ Max
Maximal oxygen uptake
How it's read
Compared with age- and sex-specific norms; higher is better
The most direct measure of cardiorespiratory fitness.
How it's read
Compared with age- and sex-specific norms; higher is better
Measured in: mL/kg/min
What results can mean
In a study of more than 122,000 patients, those with the lowest fitness had about five times the mortality of the fittest.
What reliably changes it
Aerobic exerciseInterval training
Sources: Mandsager 2018 · Helgerud 2007
📖 VO2 Max Testing: How to Measure Your Cardiorespiratory Fitness
Grip Strength
Handgrip dynamometry
How it's read
Compared with age- and sex-specific norms
Low muscle strength, usually measured by grip, is the first step in diagnosing sarcopenia.
How it's read
Compared with age- and sex-specific norms
Measured in: kg
What results can mean
In a study across 17 countries, each 5 kg lower grip strength was associated with 16% higher all-cause mortality (hazard ratio 1.16).
Resting Heart Rate
Beats per minute, at rest
How it's read
Normal 60–100 beats per minute for adults; 40–60 in well-trained athletes
Your heart rate when sitting or lying down but awake.
How it's read
Normal 60–100 beats per minute for adults; 40–60 in well-trained athletes
Measured in: beats per minute
What results can mean
Below 60 is common in fit people. In a large meta-analysis, a higher resting heart rate was associated with higher mortality.
HRV
Heart rate variability
How it's read
Highly individual; compare with your own baseline
The variation in time between heartbeats, shaped by the autonomic nervous system.
How it's read
Highly individual; compare with your own baseline
Measured in: ms
What results can mean
Used to track stress, fitness and recovery; norms depend on the measurement method.
Sources: Shaffer 2017 review
📖 Heart Rate Variability: The Real-Time Window Into Your Autonomic Nervous System
Biological Aging Clocks
4DunedinPACE
Pace-of-aging clock
How it's read
Reported as a pace of aging; higher values mean faster aging
A DNA methylation measure designed to estimate the current pace of biological aging.
How it's read
Reported as a pace of aging; higher values mean faster aging
Measured in: years of biological aging per calendar year
What results can mean
A research measure; it is not used to guide routine care.
Sources: Belsky 2022
📖 Biological Age Testing: Which Epigenetic Clocks Are Worth Using
GrimAge
Epigenetic clock
How it's read
Reported as an estimated age; the gap from your chronological age is called age acceleration
Built to predict time to death using DNA methylation stand-ins for smoking history and several blood proteins; it strongly predicted lifespan and healthspan in its developers' validation cohorts.
How it's read
Reported as an estimated age; the gap from your chronological age is called age acceleration
Measured in: years
What results can mean
A research measure; it is not used to guide routine care.
Sources: Lu 2019
📖 Biological Age Testing: Which Epigenetic Clocks Are Worth Using
Telomere Length
Leukocyte telomere length
How it's read
No clinical use; results vary by method
Telomeres shorten as cells divide, but telomere length has not been established as a reliable biomarker of aging.
How it's read
No clinical use; results vary by method
Measured in: kilobases or T/S ratio (method-dependent)
What results can mean
Longer is not simply better: genetically longer telomeres are linked to a higher risk of several cancers.
Sources: Mather 2011 review · Haycock 2017
📖 Epitalon: The Telomere Peptide — What the Evidence Actually Shows
PhenoAge
Biological age from blood tests or methylation
How it's read
Reported as an estimated age; compare with your chronological age
PhenoAge was trained on a blood-test measure of physiological age. Its DNA methylation version outperformed earlier clocks at predicting mortality.
How it's read
Reported as an estimated age; compare with your chronological age
Measured in: years
What results can mean
You can calculate the blood-based PhenoAge from nine routine tests with our biological age calculator.
Sources: Levine 2018
📖 Biological Age Testing: Which Epigenetic Clocks Are Worth Using
Related Reading
The Complete Longevity Lab Testing Guide →
ApoB: The Number Your Doctor Probably Isn't Ordering →
Fasting Insulin and HOMA-IR →
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