The 7 blood tests everyone should know about

Your lab report tells you whether you're inside the lines. These seven blood tests help you see where you are inside them.

There are a handful of blood tests everyone should know about by name, because the "normal" range on your lab report answers a different question than the one most of us are asking. Labs build reference ranges from large populations. They basically take the middle 95 percent of results and call it normal. That's a useful line. But the question I care about is a different one: at what level does this number go along with the best long-term health? That's optimal, and it's often a long way from normal.

Normal is the speed limit, not the safe speed

I explain it with the speed limit. The legal limit keeps you out of trouble with the law. It doesn't mean that speed is safe on every road, in every kind of weather. Lab reference ranges are the legal speed limit for your blood work. Staying inside them keeps you out of a diagnosis. It doesn't mean you're thriving.

Modern medicine is organized around diagnosis codes, and a number that's inside the range but not optimal has no code, so it often gets no comment. That's not a knock on doctors. I'm one myself. It's just that a lot of the system is built for sick care.

None of this replaces your doctor. The goal is to become an informed partner in your own care, because these numbers belong to you. For each test, I'll tell you what the number reflects, where the lab draws its line, and, where I have one, the range I like to see in my own patients.

The fire and the master key

1. hs-CRP (high-sensitivity C-reactive protein)

Think of hs-CRP as a smoke detector. Your liver makes CRP whenever the immune system sends out an SOS. The standard test catches big fires, like an infection. The high-sensitivity version picks up the low, smoldering inflammation you can't feel, the kind I wrote about in chronic inflammation explained.

Why it matters: a large analysis that pooled 54 long-term studies and about 160,000 people found that higher CRP went along with higher heart risk, and the link held up after accounting for the usual risk factors, though it got smaller (Emerging Risk Factors Collaboration, 2010). That's an association, not proof that CRP causes anything. But it's why I think of hs-CRP as the most direct window into inflammation we have. The number I like to see is under 1.

2. Vitamin D

Vitamin D isn't really a vitamin. It's a hormone because it gets released, travels, and hits receptors inside your cells, and those receptors are in almost every tissue of your body. I think of it as a master key that unlocks function almost everywhere.

Many labs only flag a level below 20 or 30. The range I like to see is around 40 to 50. So your doctor may say nothing at 22, well under where I'd want you.

A key needs a working lock, though. Magnesium helps convert vitamin D into its active form (think dark leafy greens). Vitamin K2 is the traffic director that tells the calcium where to go (natto, or fermented soybeans, is the richest food source). And zinc helps the receptors work (pumpkin seeds, beans). If you supplement vitamin D, ask your doctor about these partners too.

The engine: how you handle sugar

3. Fasting insulin

This is my favorite test to get on your own, and one of the least ordered, because a moderately high insulin with normal blood sugar has no diagnosis attached.

I use the nightclub picture here. Insulin is the bouncer at the door of every cell, letting blood sugar in. Over time, some cells start ignoring the bouncer. So the pancreas sends out more bouncers. Your body can keep up with that for a long while, which means your blood sugar stays completely normal while your insulin quietly climbs. By the time fasting glucose finally rises, the pancreas has often been working overtime for years. Fasting insulin can show you that early, while it tends to respond well to diet, movement, and sleep.

Years ago, a woman in one of my classes went out and got her fasting insulin, and her doctor was upset that she'd ordered it herself. But it lit a fire in her. She ordered more labs and made real changes. I've seen that pattern many times: walking into a lab for your own number is often the moment someone goes from passive recipient to active participant.

More recently, a patient in my practice told me his primary care doctor had called all his labs normal. His fasting insulin was 15. That's inside many labs' ranges, and I read it as elevated. That's the gap between normal and optimal in one number. You can also ask your doctor about a HOMA-IR, which uses fasting insulin and glucose together to estimate insulin resistance.

4. Hemoglobin A1c

A1c is your roughly three-month blood sugar average. It measures how much sugar has bound to the protein in your red blood cells. I think of it as rust forming on a pipe: the higher and longer blood sugar runs, the faster the rust builds, and that same binding is happening on proteins throughout the body, including the collagen in your skin. Once sugar binds a protein that way, it essentially doesn't come back off. More on that mechanism and why your blood sugar spikes.

The standard cutoffs doctors use are 5.7 for the prediabetes range and 6.5 for diabetes. The range I like to see is under 5.4, as close to 5 as you can get. The way I look at it, A1c is also a rough speedometer for how quickly sugar is aging your proteins. I check mine every six months; more often than every three doesn't make sense, since that's the window it reflects.

The trucks on the road: your cholesterol risk

5. ApoB (apolipoprotein B)

A standard cholesterol panel counts the cargo. ApoB counts the trucks. And it's the trucks that cause the accidents.

Every particle that can carry cholesterol into your artery walls has exactly one ApoB molecule on it, while the cholesterol inside each one varies. So ApoB counts the trucks. A review in JAMA Cardiology concluded that ApoB reflects this risk more accurately than LDL cholesterol does (Sniderman et al., 2019). Most authorities are comfortable under 100. The range I like to see is 60 to 90, or lower.

6. Lipoprotein(a)

This is one you only need once in your life, because your level is essentially set by your genes. A 2022 European consensus statement recommends that every adult have it measured at least once, and describes high Lp(a) as a risk factor even when LDL cholesterol is very low (Kronenberg et al., 2022).

It's rarely ordered, partly because there's no medication designed specifically to lower it yet. But a high result isn't a sentence. It means everything else matters more for you: your ApoB, your blood pressure, your blood sugar, your inflammation. That same consensus recommends managing those risk factors early. If yours comes back high, or there's heart disease in your family that never quite made sense, a preventive cardiologist is worth seeing.

What's actually in your cells

7. Omega-3 index

This one isn't about how much fish oil you take. It's about how much omega-3 has made it into your cells. It measures the long-chain omega-3s (EPA and DHA) in your red blood cells, so it reflects roughly the last three to four months, not yesterday's dinner.

The people who first proposed the index found that 8 percent or higher went along with the most heart protection and 4 percent or lower with the least (Harris and von Schacky, 2004). I want everyone above 6 at the very least, and above 8 if you can get there.

Why test instead of guess? Flax, chia, and walnuts carry a shorter plant omega-3, and your body converts only a small, variable fraction into the long-chain forms. If you don't eat fish, checking is the only way to know. It's a finger stick you can do at home and mail in.

The one I almost left out

As I was preparing this class, I added a genetic marker: APOE4. Like Lp(a), you only need it once. It's associated with a higher risk of Alzheimer's disease, and two copies carry more risk than one.

I hesitated because some people would rather not know. But a positive result is not a diagnosis, and it doesn't mean you'll get the disease. It's a reason to sit down with your doctor or a genetic counselor, especially if Alzheimer's runs in your family.

How to get these tests yourself

In most states, you can order these tests without a referral through direct-to-consumer services that use the big national labs. You pay online, bring your order confirmation, get your blood drawn, and the results come straight to you. A few states restrict self-ordering (New York and New Jersey among them), so check yours. Fasting insulin often runs around $20.

Then bring your numbers to your doctor. Be the educated patient. You'll get better care, and good doctors enjoy that conversation.

Questions I get about this

Do I need to fast for these?

Fasting insulin requires an overnight fast. hs-CRP, the omega-3 index and APOE4 don't. For the rest, ask the lab when you book, since instructions vary.

Will insurance cover tests I order myself?

Usually not. But you can ask your doctor to add them to your yearly blood work, and then they're typically covered. "I've been reading about fasting insulin and ApoB; can we add those?" goes a long way.

Why not just order a giant panel?

Those panels can be good. But I like to start with a short list you can understand and act on. Learn these seven first.

What about hormone panels?

I do recommend a yearly male or female hormone panel, including after menopause. But I don't manage hormones in my practice, and I only teach what I've followed with real patients, so that's a conversation for a doctor who specializes in it.

References

1. Emerging Risk Factors Collaboration, Kaptoge S, et al. C-reactive protein concentration and risk of coronary heart disease, stroke, and mortality: an individual participant meta-analysis. The Lancet. 2010. PubMed
2. Sniderman AD, et al. Apolipoprotein B particles and cardiovascular disease: a narrative review. JAMA Cardiology. 2019. PubMed
3. Kronenberg F, et al. Lipoprotein(a) in atherosclerotic cardiovascular disease and aortic stenosis: a European Atherosclerosis Society consensus statement. European Heart Journal. 2022. PubMed
4. Harris WS, von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease? Preventive Medicine. 2004. PubMed