The 12 Most Important Blood Tests, Explained by a Physician

What your annual physical misses and what comprehensive testing actually reveals

By Dr. Eve Henry, Internal Medicine Physician and Chief Medical Officer at Hundred Health

Most people get a blood test once a year, look at the little "H" or "L" next to their results, and assume everything is fine if their doctor doesn't call. 

Here's the problem with that: standard lab panels were designed to catch disease, not necessarily to optimize health. It’s part of a reactive model; waiting to find the problem until  it’s already causing symptoms or has pushed biomarkers well out of the normal range. 

That's not the same as understanding how your body is actually functioning.

I've spent years in primary care because I believe the gap between "not sick" and "thriving" is enormous and that gap is measurable. Blood biomarkers are one of the most powerful tools we have to close it. But only if you're testing the right things, in the right context, with someone who can help you understand what the numbers actually mean for your life.

So let me walk you through the blood tests that matter most — what they measure, why they matter, and what we look at inside Hundred Health's comprehensive testing protocol.

Why Most Annual Bloodwork Isn't Enough

Your annual physical typically includes a complete blood count, a basic metabolic panel, and maybe a lipid panel. That's roughly 14 to 20 markers. It's a starting point. But it leaves enormous blind spots.

It won't tell you whether your insulin or Hba1c is creeping up years before your glucose becomes a problem. It won't catch thyroid dysfunction if your TSH looks "normal" but your free T4 or free T3 is suboptimal. It won't show you that your ApoB — one of the most predictive markers for cardiovascular risk — is elevated even when your LDL looks fine on paper.

The reality is that the standard panel was designed for population-level screening, not individual optimization. And if you're someone who wants to understand what's actually happening in your body — not just whether you've crossed a clinical threshold — you need more.

At Hundred, we test 100+ biomarkers across every major system. Here's what that looks like in practice, and why each category matters.

The 12 Essential Blood Tests for Longevity and Disease Prevention

TL;DR — The 12 Essential Blood Tests include:

1. ApoB (Heart)

2. Lp(a) (Heart)

3. LDL-P (Heart)

4. Fasting Insulin (Metabolism)

5. HbA1c (Metabolism)

6. Leptin (Metabolism)

7. Free T3 (Thyroid)

8. Free T4 (Thyroid)

9. ALT/AST (Liver)

10. GGT (Liver)

11. eGFR (Kidney)

12. Uric Acid (Metabolic/Kidney)

Advanced Heart Health: Moving Beyond Basic Cholesterol

The lipid panel most people get checks total cholesterol, LDL, HDL, and triglycerides. That's useful. But it's a bit like checking whether your car has gas without looking at the engine.

Here's what I mean. LDL-C — the number on your standard lipid panel — is a measure of cholesterol mass or weight.  What it doesn't tell you is the number of LDL particles circulating in your blood, or how small and dense those particles are. Small, dense LDL particles are more likely to penetrate arterial walls and contribute to plaque formation than large, buoyant ones. Two people can have identical LDL-C numbers and wildly different cardiovascular risk profiles.

ApoB (Apolipoprotein B): The Best Predictor of Heart Risk

ApoB is arguably the single best predictor of cardiovascular risk that exists — and it's almost never included in a standard lipid panel. Here's why it matters: every atherogenic particle (the kind that causes plaque) carries exactly one ApoB molecule. So rather than estimating cholesterol mass, ApoB gives you a direct count of the dangerous particles circulating in your blood. 

Think of LDL-C as measuring how heavy a crowd of people is. ApoB tells you how many people are actually in the room. 

At Hundred, we test ApoB as a core cardiovascular marker in every panel — because getting your LDL-C "normal" while missing elevated ApoB is exactly the kind of false reassurance that leads to surprise heart attacks.

Lp(a) and LDL Particle Size: Identifying Hidden Cardiovascular Stress

Lipoprotein(a), or Lp(a), is genetically determined — you can't change it with diet or exercise — and about 20% of the population has dangerously elevated levels without knowing it. It's an independent risk factor for cardiovascular disease that the standard cholesterol panel completely misses.

We also measure LDL Particle Number (LDL-P) and Small LDL Particle Number — because particle size matters as much as particle count. Small, dense LDL particles oxidize more easily and penetrate arterial walls more readily than large, buoyant ones. Two people with identical LDL-C readings can have very different actual risk once you look at particle size and count.

Rounding out heart health: we also test Non-HDL Cholesterol, HDL Particle Size, and Triglycerides, because elevated triglycerides combined with low HDL is a pattern that signals metabolic dysfunction — often years before diabetes develops.

Metabolic Health: Detecting Insulin Resistance Early

This is the one that surprises people most in my practice. Insulin resistance — the root cause of type 2 diabetes, metabolic syndrome, and a significant driver of cardiovascular disease — can be present for a decade or more before your fasting glucose becomes abnormal.

By the time your blood sugar is elevated, you've often already lost significant insulin sensitivity. The window for easy intervention has narrowed considerably.

Fasting Insulin vs. Glucose: Why Your Annual Lab Misses Early Warning Signs

Your standard panel tests fasting glucose. What it almost never tests is fasting insulin — and that's the critical gap.

Here's the mechanism: when your cells start becoming resistant to insulin, your pancreas compensates by producing more of it to keep blood sugar in check. So your glucose looks normal. Your A1c looks normal. But underneath, your insulin is elevated — working overtime to maintain the appearance of metabolic health.

Elevated fasting insulin is often the earliest detectable sign of insulin resistance, appearing years before glucose rises. Once you know your fasting insulin is trending up, you have a meaningful window to intervene through dietary changes, exercise timing, sleep optimization, and targeted protocols — before the problem becomes structurally harder to reverse.

We test both at Hundred, every cycle, because you cannot understand your metabolic health from glucose alone.

HbA1c and Leptin: Mapping Your Long-Term Blood Sugar Health

Hemoglobin A1c (HbA1c) gives you your average blood sugar over the past two to three months — a far more informative picture than a single fasting glucose reading, which can vary based on what you ate the night before, how well you slept, and your stress level that morning.

Leptin is the piece most people have never heard of. It's a hormone produced by fat cells that regulates hunger and metabolism. Leptin resistance — where your brain stops responding to leptin's satiety signals — is closely intertwined with insulin resistance and is a reliable early marker of metabolic dysfunction. It's rarely tested in conventional settings because it doesn't fit neatly into the "diagnose disease" framework. But if you're trying to understand why weight loss feels harder than it should, or why your energy crashes after meals, leptin is part of the picture.

Comprehensive Thyroid Panels: Why TSH Isn't the Whole Story

Your thyroid is running the background processes of your entire body — metabolism, energy, mood, body temperature, heart rate, cognitive function. When it's off, everything feels off. And yet the standard thyroid test most people get is just TSH.

TSH is the signal your brain sends to your thyroid. It tells you whether your brain thinks your thyroid needs to work harder. What it doesn't tell you is whether your thyroid is actually producing adequate hormones, or whether your body is converting those hormones into their active form.

Free T3 and Free T4: Measuring Active Hormone Levels

Here's the mechanism that gets missed: your thyroid produces mostly T4 (thyroxine), which is essentially an inactive form. Your body then converts T4 into T3 (triiodothyronine) — the active hormone that actually does the work at the cellular level. Some people have normal TSH and normal T4 but poor T4-to-T3 conversion, meaning their cells are functionally hypothyroid even though the standard test looks fine.

Free T4 tells you how much of the unbound, available inactive thyroid hormone you have circulating. Free T3 tells you how much active hormone your cells are actually receiving. TSH alone tells you neither.

If you've been told your thyroid is "normal" but you're still exhausted, gaining weight, struggling with brain fog, or feeling cold all the time — a full thyroid panel including Free T3 and Free T4 is worth having. We test all four markers at Hundred: TSH, Free T4, Free T3, and Total T4, because the short answer is that TSH alone doesn't complete the story.

Liver and Kidney Function: Monitoring Your Body's Filtration System

These organs are doing constant, unglamorous work — filtering toxins, metabolizing medications, regulating fluid balance, producing proteins your blood needs to function. They're also remarkably resilient, which means dysfunction can be well underway before you feel it.

ALT, AST, and GGT: Essential Markers for Liver Health

ALT (Alanine Transaminase) and AST (Aspartate Transaminase) are enzymes that leak into the bloodstream when liver cells are damaged. Elevated levels can indicate fatty liver disease, medication effects, or alcohol-related damage — and non-alcoholic fatty liver disease in particular can progress silently for years before causing symptoms.

GGT (Gamma-Glutamyl Transferase) is often the more sensitive early warning. It responds to alcohol intake and oxidative stress and may rise before ALT and AST do. If your GGT is trending up while your ALT and AST still look normal, that's a signal worth paying attention to.

We also test Alkaline Phosphatase (ALP), Albumin, Total Protein, and Total Bilirubin — because liver health isn't a single number. It's a pattern across multiple markers that together tell you how well your liver is both processing waste and performing its synthetic functions.

eGFR and Creatinine: Assessing Kidney Filtration Efficiency

Creatinine and BUN (Blood Urea Nitrogen) are waste products that your kidneys filter out. When kidney function declines, they accumulate in the blood. The problem is that creatinine doesn't rise above the normal range until you've already lost roughly 50% of kidney function — so catching problems early requires going further.

eGFR (Estimated Glomerular Filtration Rate) is calculated from creatinine, age, and sex, and is the standard measure of kidney filtration capacity. We also test Uric Acid — elevated levels are associated with gout, kidney stones, and increasingly recognized as an independent marker of metabolic dysfunction and cardiovascular risk — and Microalbumin in urine, which detects tiny amounts of protein leaking into the urine before creatinine or eGFR show any abnormality.

That last one matters. Microalbuminuria is often the earliest detectable sign of kidney stress, and standard lab panels almost never include it.

We also run a comprehensive urinalysis — 30+ urine markers — because urine tells a story that blood alone can't.

Hormones: The Conversation Your Body Is Having With Itself

Hormones are the signaling molecules that coordinate virtually everything — energy, mood, libido, muscle mass, bone density, sleep quality, cognitive function. They change with age, stress, sleep, nutrition, and a dozen other variables. And they interact with each other in ways that make single-hormone testing genuinely incomplete.

For women, we test:

• Estradiol — the primary estrogen; critical for bone health, cardiovascular protection, cognitive function, and mood

• Progesterone — often overlooked, but essential for sleep quality, anxiety regulation, and estrogen balance

• Total and Free Testosterone — yes, women need testosterone too. It affects energy, libido, muscle mass, and motivation

• FSH and LH — pituitary hormones that regulate the menstrual cycle and signal reproductive status

• SHBG (Sex Hormone Binding Globulin) — the protein that binds sex hormones; high SHBG can leave you with low free hormone levels even when total levels look adequate

• Prolactin — elevated levels can suppress ovulation and cause symptoms that mimic other hormonal imbalances

• IGF-1 (Insulin-Like Growth Factor 1) — reflects growth hormone activity; important for muscle maintenance, metabolism, and cellular repair

For men, we test the same panel with the addition of PSA (Prostate Specific Antigen) for prostate health monitoring because men's hormonal health is equally complex and equally undertested.

The pattern I see most often: people with symptoms that have been dismissed or attributed to "just getting older" — fatigue, weight gain, mood changes, low libido, poor sleep — who have hormonal imbalances that are entirely addressable once you actually look.

Inflammation: The Slow Fire

Chronic low-grade inflammation is implicated in virtually every major chronic disease — cardiovascular disease, type 2 diabetes, Alzheimer's, cancer, autoimmune conditions. It's also one of the most modifiable risk factors we have.

High-Sensitivity CRP (hs-CRP) is the most clinically validated marker of systemic inflammation. Standard CRP tests aren't sensitive enough to detect the low-level inflammation that predicts cardiovascular risk. The high-sensitivity version is — and the difference matters enormously for catching risk early.

We also test ANA (Antinuclear Antibodies), which screens for autoimmune activity. A positive ANA can precede clinical autoimmune disease by years, giving you a window for intervention well before symptoms become disruptive.

Elevated hs-CRP in the absence of acute infection is a signal worth taking seriously. It often reflects dietary patterns, sleep quality, gut health, or chronic stress — all of which are addressable with the right direction.

Nutrient Levels: What Your Body Is Actually Working With

You can eat a "healthy diet" and still be deficient in key nutrients — because absorption varies enormously based on gut health, genetics, medications, and age. Deficiencies in these nutrients don't just cause symptoms; they impair the function of every other system we've discussed.

What we test:

• Vitamin D — functions more like a hormone than a vitamin, with receptors in virtually every tissue. It affects immune function, mood, bone density, cardiovascular health, and cancer risk. Optimal levels are not the same as "not deficient" — and most people with "normal" vitamin D are well below the range associated with health benefits

• Ferritin — the storage form of iron. Low ferritin causes fatigue, hair loss, poor exercise tolerance, and cognitive fog — often before hemoglobin drops enough to show anemia on a standard CBC. It's one of the most commonly missed causes of exhaustion I see in practice

• Iron, TIBC, and Iron Saturation — the full iron picture, not just a single number

• Magnesium — involved in over 300 enzymatic reactions. Most people are mildly deficient, and standard serum magnesium is a poor indicator of true body stores because magnesium is tightly regulated in the blood even when tissue levels are depleted

• Zinc — essential for immune function, wound healing, testosterone production, and taste and smell

• Homocysteine — an amino acid that, when elevated, is an independent risk factor for cardiovascular disease and cognitive decline. It's also a sensitive marker of B vitamin status (B6, B12, folate) — and a target that responds reliably to supplementation

Stress, Aging, and Biological Age

This is where Hundred's approach gets genuinely different from anything you'll find in a standard lab panel.

Cortisol — your primary stress hormone — affects virtually every system in your body. Chronically elevated cortisol suppresses immune function, promotes fat storage (particularly visceral fat), impairs sleep, and accelerates cellular aging. Most people know stress is bad for them. Far fewer have actually measured what their cortisol is doing.

IGF-1 reflects growth hormone activity, which declines with age and affects muscle maintenance, fat metabolism, and cellular repair. Tracking it gives you insight into one of the key biological mechanisms behind how we age.

And then there's biological age — a composite score calculated from eight specific biomarkers that research has shown to correlate with actual aging rate, independent of chronological age. At Hundred, we calculate this from white blood cell count, alkaline phosphatase, glucose, lymphocytes, creatinine, mean corpuscular volume (MCV), red cell distribution width (RDW), and albumin.

This isn't a gimmick. The biological age calculation is based on validated research, and it gives you something genuinely useful: a number that reflects how your body is aging, and that changes in measurable ways in response to the interventions you make. I've seen people improve their biological age by years within a single 100-day cycle by addressing the specific markers that were driving the score.

Heavy Metals: The Exposure You Didn't Know You Had

We also test for lead — because lead exposure isn't just a historical problem. It accumulates in bone over a lifetime and can be remobilized during periods of bone loss, including menopause and osteoporosis. Elevated lead levels are associated with cardiovascular disease, cognitive decline, and kidney dysfunction.

This is the one that surprises people most. Most assume they haven't been exposed. Many have been — through older housing, certain occupational environments, imported goods, or simply cumulative lifetime exposure that adds up over decades.

What Makes Hundred Different

Here's what I want you to understand about how we use all of this data.

A list of 100+ biomarkers is only useful if someone helps you make sense of it. The problem with most lab testing — even comprehensive panels — is that you get a PDF full of numbers with reference ranges, and you're left to figure out what it means for you.

At Hundred, your results don't exist in isolation. They're interpreted in the context of your medical history, your lifestyle, your goals, your wearable data, and the evidence base for what actually moves the needle for people like you. That's the decision layer that's been missing from health optimization.

Your annual physical tests 14 markers and sends you home. Hundred tests 160+, connects your wearables and medical history, and gives you a 100-day protocol built from all of it.

The goal isn't to give you more data. It's to give you clarity about what to do next.

A Note on Testing Frequency

We test twice a year at minimum, no sooner than a 100-day cycle — at the beginning and at the end. This isn't arbitrary. It's enough time for meaningful biological change to occur in response to interventions, and it gives you a before-and-after picture that makes your progress visible and measurable.

Health is not a one-time event. It's an iterative process. And the data should reflect that.

The Bottom Line

Blood testing is one of the most powerful tools we have for understanding what's happening inside your body. But the standard annual panel was designed for a different purpose — catching disease, not optimizing health.

If you want to understand your cardiovascular risk beyond basic cholesterol, catch metabolic dysfunction before it becomes diabetes, optimize your hormones, identify nutrient deficiencies that are quietly limiting your energy and cognition, and track your biological age over time — you need a more comprehensive approach.

That's what we built Hundred to do.

Stop Guessing. Start Optimizing.

Your annual physical typically tests 14 markers and sends you home with a "normal" bill of health. At Hundred Health, we believe you deserve a more complete picture.

We test 100+ advanced biomarkers — from ApoB and fasting insulin to full thyroid and hormone panels — and combine them with your medical history and wearable data to build your baseline.

Ready to see what's actually happening inside your body?

See Our Full List of 160+ Biomarkers — Explore every system we measure, from heart health to metabolic function.

Join Hundred Health Today — Get two comprehensive lab draws per year, clinician-reviewed insights, and a personalized 100-day action plan for just $1.37/day ($499/year).

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Dr. Eve Henry is an internal medicine physician and Chief Medical Officer at Hundred Health. She specializes in evidence-based approaches to healthspan optimization, hormonal health, and metabolic function.

Hundred Health is HIPAA Compliant, CLIA Certified, CAP Accredited, and a Quest Diagnostics Partner. Testing is HSA/FSA eligible.