A practical guide to the blood tests that matter for aging well

The Numbers That Matter

Blood tests are windows into your body's internal state. They can reveal problems years before symptoms appear and track whether interventions are actually working.

But here's the challenge: standard lab ranges are designed to identify disease, not optimize health. A result marked "normal" often just means "not sick enough to diagnose." As Steve Horvath, the UCLA and Altos Labs researcher who pioneered epigenetic aging clocks, has noted based on recent 2025 research, "conventional clinical biomarkers capture disease states, but we're now learning that molecular signatures can reveal biological age decades before disease manifests." For healthy aging, we need to think differently about these numbers.

This guide covers the key biomarkers relevant to aging: what they measure, why they matter, and what ranges to aim for. We'll focus on tests most people can get through their regular doctor, with context on how to interpret the results.

This connects directly to the science of measuring biological age. While biological age clocks provide a composite measure, individual biomarkers give you specific, actionable information about what's happening inside your body.

Understanding Lab Ranges

Before we get to specific markers, an important concept: the difference between "normal" and "optimal."

Standard reference ranges are typically set to include 95% of the population tested by a given lab. If you fall within that range, you're "normal." But normal includes a lot of people who are metabolically unhealthy, chronically inflamed, or on the path to disease.

Research consistently shows that values at the edges of normal ranges often predict worse health outcomes. Someone with fasting glucose of 99 mg/dL (technically normal) has meaningfully different risk than someone at 80 mg/dL.

Optimal ranges aim for where healthy, metabolically fit people actually land, not where the general (often unhealthy) population averages out. Throughout this guide, we'll provide both standard and optimal ranges where the research supports a distinction.

Metabolic Health Markers

These markers tell you how well your body is handling glucose and metabolic function. They're particularly important because metabolic dysfunction underlies many age-related conditions.

Fasting Glucose

What it measures: Blood sugar level after overnight fasting. Reflects your baseline glucose regulation.

Standard range: Below 100 mg/dL is normal; 100-125 is prediabetic; 126+ is diabetic.

Optimal range: 70-85 mg/dL. Being at the high end of "normal" isn't benign. Values consistently above 90 mg/dL, while technically normal, are associated with higher risk over time.

Why it matters: Chronically elevated glucose damages blood vessels, promotes inflammation, and accelerates aging processes. Even modestly elevated levels in the "normal" range predict higher cardiovascular risk.

HbA1c (Glycated Hemoglobin)

What it measures: Average blood sugar over the past 2-3 months. More useful than fasting glucose alone because it captures glucose control over time, including after meals.

Standard range: Below 5.7% is normal; 5.7-6.4% is prediabetic; 6.5%+ is diabetic.

Optimal range: Below 5.5%, with some longevity researchers suggesting below 5.0% as ideal. Studies show that glycemic control is a causal mechanism for healthspan maintenance. Morgan Levine, Principal Investigator at Altos Labs who developed the PhenoAge biological age clock, emphasizes that current evidence as of 2026 shows "metabolic markers like HbA1c aren't just disease indicators. They're fundamental components of biological aging that we can measure and modify."

Why it matters: HbA1c is one of the most validated predictors of age-related disease. Higher values, even within normal range, predict cardiovascular disease, cognitive decline, and mortality.

Fasting Insulin

What it measures: Insulin level after overnight fasting. Unlike glucose, which stays normal until disease is advanced, insulin rises early in the process of metabolic dysfunction.

Standard range: 2.6-24.9 μIU/mL is the typical reference range, though this varies by lab.

Optimal range: Below 8 μIU/mL, and ideally below 5-6 μIU/mL. Values consistently above 10-12 μIU/mL suggest developing insulin resistance even when glucose looks normal.

Why it matters: Fasting insulin can identify metabolic problems 10-20 years before type 2 diabetes diagnosis. It's one of the earliest warning signals of metabolic dysfunction.

HOMA-IR

What it measures: Homeostatic Model Assessment of Insulin Resistance. A calculation from fasting glucose and insulin that estimates insulin sensitivity.

Standard range: Below 2.5 is considered normal by most standards, though cutoffs vary.

Optimal range: Below 1.0 indicates excellent insulin sensitivity. Values above 2.0-2.5 suggest insulin resistance; above 3.0 is significantly elevated.

Why it matters: HOMA-IR integrates glucose and insulin data to give a more complete picture of metabolic health. It can detect subtle insulin resistance before other markers change.

Inflammatory Markers

Chronic low-grade inflammation, sometimes called "inflammaging," is one of the key drivers of biological aging. These markers help you track inflammatory status.

C-Reactive Protein (hs-CRP)

What it measures: An acute-phase protein produced by the liver in response to inflammation. The high-sensitivity version (hs-CRP) is needed to detect low-grade chronic inflammation.

Standard range: Below 3.0 mg/L is considered normal for cardiovascular risk assessment.

Optimal range: Below 1.0 mg/L, with below 0.5 mg/L being ideal. Research shows that participants in the highest CRP quartile (above 3.06 mg/L) had nearly double the mortality risk compared to the lowest quartile (below 0.41 mg/L).

Why it matters: Chronic systemic inflammation underlies many chronic diseases, including cardiovascular disease, cancer, diabetes, kidney disease, liver disease, and neurodegenerative disease. CRP is a general marker that can detect this low-grade inflammatory state.

Context note: CRP is non-specific. It can be elevated from acute infection, injury, or temporary inflammation. One elevated reading isn't conclusive. Look for patterns across multiple tests.

Other Inflammatory Markers

If CRP is elevated, additional testing may help identify sources:

ESR (Erythrocyte Sedimentation Rate): Another general inflammation marker, useful in combination with CRP
Ferritin: While primarily an iron marker, high ferritin can indicate inflammation
Homocysteine: Elevated levels are associated with cardiovascular inflammation and cognitive decline

Lipid Panel

Heart disease remains a leading cause of death. Lipid markers help assess cardiovascular risk, though interpretation has evolved beyond simple LDL targets.

LDL Cholesterol

What it measures: Low-density lipoprotein cholesterol, the primary carrier of cholesterol in blood. Often called "bad cholesterol," though the picture is more nuanced.

Standard range: Below 100 mg/dL is optimal by conventional guidelines; below 70 mg/dL is recommended for those with existing heart disease.

Optimal range: Below 100 mg/dL (2.6 mmol/L), with some longevity-focused practitioners targeting below 80 mg/dL in low-risk individuals and below 50-70 mg/dL in higher-risk individuals.

Why it matters: LDL cholesterol contributes to atherosclerotic plaque formation. Lower is generally better from a cardiovascular standpoint, though the benefit of aggressive lowering in healthy individuals without risk factors is debated.

HDL Cholesterol

What it measures: High-density lipoprotein cholesterol. Involved in reverse cholesterol transport, moving cholesterol from arteries back to the liver.

Standard range: Above 40 mg/dL for men, above 50 mg/dL for women.

Optimal range: Above 60 mg/dL (1.5 mmol/L), with 60-80 mg/dL often cited as ideal. Very high HDL (above 100 mg/dL) doesn't appear to provide additional benefit and may even be harmful in some contexts.

Why it matters: Higher HDL is associated with lower cardiovascular risk, though the relationship is complex and HDL function matters more than just the number.

Triglycerides

What it measures: Fat in the blood, primarily influenced by recent diet (especially carbohydrates and alcohol) and metabolic health.

Standard range: Below 150 mg/dL is normal.

Optimal range: Below 100 mg/dL, with below 70 mg/dL being excellent. Elevated triglycerides are often an early sign of metabolic dysfunction.

Why it matters: High triglycerides, especially in combination with low HDL, indicate metabolic dysfunction and increased cardiovascular risk.

Triglyceride/HDL Ratio

Why it matters: This ratio is particularly predictive of cardiovascular risk and insulin resistance. Optimal is below 2.0; above 3.0 suggests metabolic problems.

ApoB and Lp(a)

Standard lipid panels are being supplemented by more predictive markers:

ApoB (Apolipoprotein B): Measures the actual number of atherogenic (plaque-forming) particles rather than just cholesterol content. May be more predictive of cardiovascular risk than LDL-C alone. Optimal is below 80 mg/dL.

Lp(a) (Lipoprotein a): A genetic risk factor that standard lipid panels miss. If elevated (above 30-50 mg/dL depending on units), it significantly increases cardiovascular risk regardless of other lipid numbers. This is largely genetically determined and doesn't respond much to lifestyle intervention, but knowing your level helps inform overall risk assessment.

Kidney and Liver Function

These organs are critical for metabolism, detoxification, and overall health. Function declines with age, but severe decline is preventable and early detection matters.

Creatinine and GFR

What it measures: Creatinine is a waste product filtered by kidneys. GFR (glomerular filtration rate) is calculated from creatinine and estimates kidney function.

Standard range: GFR above 60 mL/min/1.73m² is normal; below 60 indicates chronic kidney disease.

Optimal range: Above 90 mL/min/1.73m². GFR naturally declines with age, but values above 90 in older adults indicate excellent kidney function.

Cystatin C

What it measures: An alternative marker of kidney function that may be more accurate than creatinine, especially in older adults.

Why it matters: Research shows cystatin C has the largest standardized effect size of all blood biomarkers for mortality risk. A 22% increase in mortality hazard was found for each standard deviation increase in cystatin C.

Liver Enzymes (ALT, AST)

What it measures: Enzymes released when liver cells are damaged.

Standard range: ALT below 33 U/L for men, below 25 U/L for women; AST below 40 U/L.

Optimal range: ALT below 20 U/L suggests healthy liver function. Elevated ALT, even within normal range, can indicate fatty liver disease, which is increasingly common and accelerates metabolic aging.

Albumin

What it measures: The most abundant protein in blood, produced by the liver.

Standard range: 3.5-5.5 g/dL.

Optimal range: Higher albumin levels in well-hydrated individuals are associated with younger biological age. Low albumin can indicate liver disease, kidney disease, inflammation, or malnutrition, and is a robust marker of frailty.

Hormones

Hormones regulate nearly every bodily function. Several key hormones change with age, affecting metabolism, muscle mass, energy, and cognition.

Testosterone (Men)

What it measures: Primary male sex hormone. Declines gradually starting around age 30, with free testosterone declining faster than total testosterone.

Standard range: 300-1,000 ng/dL for total testosterone (varies by lab and age).

Optimal range: Context-dependent. Some men feel best at higher-normal levels (600-800 ng/dL), while others function well at lower levels. Symptoms matter more than numbers alone.

Why it matters: Low testosterone is associated with reduced muscle mass, bone density, energy, and cognitive function. However, testosterone replacement therapy has trade-offs and isn't appropriate for everyone.

DHEA-S

What it measures: Dehydroepiandrosterone sulfate, an adrenal hormone that serves as a precursor to other sex hormones. Declines significantly with age in both men and women.

Standard range: Varies widely by age and sex.

Why it matters: DHEA-S is associated with immune function, stress response, and overall vitality. Low levels correlate with frailty and mortality in older adults. Exercise can help maintain DHEA-S levels.

Thyroid (TSH, Free T4, Free T3)

What it measures: Thyroid function, which regulates metabolism.

Standard range: TSH 0.4-4.0 mIU/L (though this range is debated).

Optimal range: Many practitioners suggest TSH 1.0-2.5 mIU/L represents optimal thyroid function. Both hypothyroidism (high TSH) and hyperthyroidism (low TSH) affect energy, weight, heart function, and cognition.

Cortisol

What it measures: Primary stress hormone.

Why it matters: While basal cortisol may remain stable or slightly increase with age, the circadian rhythm flattens, leading to prolonged tissue exposure to glucocorticoids. This contributes to metabolic dysfunction, cognitive decline, and immune suppression.

IGF-1 (Insulin-like Growth Factor 1)

What it measures: A growth hormone mediator involved in tissue growth and repair. Declines approximately 1-2% per year after puberty.

Why it matters: The relationship with longevity is complex. Very high IGF-1 may accelerate aging and increase cancer risk, while very low IGF-1 is associated with frailty and muscle loss. Middle-range values are likely optimal.

Practical Recommendations

What to Test

For most adults interested in tracking aging-relevant biomarkers, a reasonable panel includes:

Essential (ask your doctor):

Complete metabolic panel (glucose, kidney function, liver enzymes, electrolytes)
Lipid panel (total cholesterol, LDL, HDL, triglycerides)
HbA1c
Complete blood count
Thyroid (TSH, ideally free T4)

Highly valuable additions:

hs-CRP (high-sensitivity C-reactive protein)
Fasting insulin
ApoB
Vitamin D

Consider based on risk factors:

Lp(a) (test once; it's genetic and doesn't change much)
Cystatin C
Homocysteine
Hormone panels (testosterone, DHEA-S) if symptoms suggest deficiency

Testing Frequency

For most healthy adults: annually for basic panels, with additional testing if results are concerning or interventions are being tracked.

More frequent testing (every 3-6 months) may be appropriate when:

Actively intervening to change a marker
Tracking response to medication
Managing a chronic condition

How to Get Tested

Through your doctor: Most primary care physicians will order basic panels. You may need to specifically request markers like fasting insulin, hs-CRP, or ApoB.

Direct-to-consumer labs: Companies like Quest, Labcorp, and various startups allow ordering tests without a doctor's order, though insurance may not cover them.

Interpretation: Getting numbers is the easy part. Interpreting them in context requires understanding trends over time, your individual circumstances, and the limitations of any single measurement.

The Bigger Picture

Biomarkers are tools, not endpoints. A low HbA1c is only valuable because it reflects (and predicts) good metabolic health. The goal isn't to optimize numbers for their own sake.

Several important caveats:

One test doesn't tell the story. Trends over time matter more than any single value. A temporarily elevated CRP during an infection means something different than chronically elevated CRP.

Normal isn't optimal. Standard reference ranges capture what's common in a population that includes many unhealthy people. Optimal ranges aim for where healthy people actually land.

Context matters. A marathon runner may have temporarily elevated inflammatory markers. A person recovering from illness may have temporarily abnormal values. Don't over-interpret single data points.

Lifestyle first. The same interventions that improve biomarkers also improve health by every other measure: exercise, nutrition, stress management. As Nir Barzilai, Director of the Institute for Aging Research at Albert Einstein College of Medicine who has studied centenarians for decades, observes, "in our studies of people who live to 100, we find that favorable biomarker profiles often reflect lifelong healthy behaviors more than genetics or supplements." If you're not doing those, focusing on biomarkers is putting the cart before the horse.

The value of biomarker tracking is catching problems early, confirming that interventions are working, and having objective data to guide decisions. They're part of understanding what's happening as you age, alongside how you feel, how you function, and how you're living.

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