A Science-Based Look at Direct-to-Consumer Blood Testing 

Imagine walking into a store and buying a machine that could tell you everything about your car: every tiny scratch, every minor rattle, every bolt that might someday wiggle loose. Sounds helpful, right? But what if that machine scared you about problems that would never actually cause trouble? What if it made you spend thousands of dollars fixing things that weren’t really broken? 

That’s basically what’s happening with companies like Function Health, which offer extensive blood testing directly to consumers. For about $500 a year, you can get more than 100 different blood tests, far more than your doctor would ever order. It sounds like a dream for anyone who wants to take charge of their health. But as scientists and doctors are discovering, more information isn’t always better information.  

What Exactly Are These Companies Selling? 

Direct-to-consumer (DTC) testing companies let you order blood tests without going through your doctor. You sign up online, visit a lab to have your blood drawn, and get your results through an app or website. The companies promise to help you catch health problems early, track your wellness over time, and become a more informed patient. 

These aren’t fake tests. Many use the same labs your doctor would use. The blood work itself is often legitimate. The problem isn’t the testing technology. The problem is what happens when healthy people go hunting for problems in their bodies without proper guidance about what those numbers actually mean. 

The Biggest Problem: Finding Things That Aren’t Really Problems 

Here’s where things get complicated. When you test for 100+ different things in your body, something is almost guaranteed to come back “abnormal.” This is just how statistics work. If a “normal range” is defined as what 95% of healthy people have, then by pure chance, about 5% of any test result will fall outside that range, even in perfectly healthy people. 

Research has found that DTC testing services flag abnormal results about 1.6 times more often than traditional medical laboratories. That’s a lot of red flags popping up for people who may be completely fine. 

Scientists call this “overdiagnosis,” which means finding and labeling conditions that would never have caused any symptoms or harm. One doctor shared a cautionary tale: his patient had a full-body scan that found a cyst. Even though the patient felt fine and had no symptoms, the cyst had to be investigated. He ended up in the hospital for five days with complications from a surgery to remove something that turned out to be completely harmless. 

What Does Science Actually Say About Comprehensive Testing? 

Here’s the surprising truth that most people don’t want to hear: large scientific studies have repeatedly shown that giving healthy people comprehensive health screenings doesn’t actually help them live longer or stay healthier. 

A major Cochrane review, one of the gold standards in medical research, analyzed 15 large clinical trials involving nearly 252,000 people. The conclusion? General health checks had essentially no effect on whether people died from any cause, from heart disease, or from cancer. People who got regular comprehensive screenings didn’t live any longer than people who didn’t. 

The screenings did find more diagnoses. People who got checked discovered more “problems.” But having those problems discovered didn’t translate into living longer or better lives. As the researchers put it: “Systematic offers of health checks are unlikely to be beneficial and may lead to unnecessary tests and treatments.” 

Most of These Tests Aren’t Recommended by Medical Guidelines 

When researchers looked at 92 laboratory screening tests marketed by DTC companies, they found that only 12% were actually recommended by evidence-based medical guidelines, and even those were only recommended for specific groups of people, not everyone. Zero of the tests were recommended for general screening of the entire population. In fact, medical guidelines actually recommended against nearly one quarter of the tests being sold. 

Why would guidelines recommend against a test? Because sometimes knowing something creates more harm than not knowing it, especially when there’s nothing useful you can do with that information, or when the test is unreliable in people without symptoms. 

The Real Harms: More Than Just Wasted Money 

The most common risks associated with frequent blood biomarker testing by DTC companies include: 

Overdiagnosis and false-positive results: As mentioned, casting a wide net catches a lot of things that don’t matter. Each “abnormal” result can lead to more testing, specialist visits, and sometimes even unnecessary procedures, all carrying their own risks. 

Anxiety and confusion: Getting a concerning result without proper context is stressful. Studies show that 56% of DTC testing products don’t offer consultation services to help people understand their results. Users report feeling overwhelmed by data, with “borderline” results creating worry about problems that may never materialize. 

Inappropriate testing: Many tests simply aren’t designed for screening healthy people. A test that works well for diagnosing someone who’s sick may perform poorly in someone without symptoms. 

Cascade effects: One slightly abnormal result leads to more tests, then maybe a specialist visit, then maybe a procedure, creating a domino effect of medical interventions that may have started from something meaningless. 

Quality concerns: Research has found significant differences between testing services, with 68% of common lab measurements showing significant variation between providers. About half of DTC products don’t even report their laboratory accreditation. 

The Supplement Trap: Throwing Pills at Numbers 

Here’s where the business model gets particularly questionable. Many DTC testing companies don’t just show you your results and wish you luck. They recommend supplements to “fix” your abnormal numbers. Function Health has faced criticism for aggressively cross-promoting supplements alongside test results. See a low number? Here’s a pill for that. Yellow flag on your dashboard? There’s a supplement that might help. 

This sounds logical on the surface. Low vitamin D? Take vitamin D. Low magnesium? Pop some magnesium. But there’s a fundamental problem with this approach: there’s often no proof that raising a number with supplements actually improves your health. 

Remember what we said about “normal ranges”? They’re statistical constructs based on population averages. What’s normal for one person might be slightly different for another based on genetics, age, diet, activity level, and countless other factors. A value that falls just outside the reference range might be perfectly normal for you. Taking supplements to push that number into the “green zone” on your app doesn’t mean you’ve made yourself healthier. You’ve just changed a number. 

The harsh truth is that for most biomarkers, we simply don’t have evidence that supplement interventions improve actual health outcomes like living longer, having fewer heart attacks, or avoiding disease. The supplement industry is a $50+ billion market built largely on the assumption that more nutrients equals better health, but clinical trials frequently fail to support this idea. 

There are a few legitimate exceptions among the biomarkers that companies like Function Health test. Omega-3 fatty acids have decent evidence for improving triglycerides and omega-3 index assuming you have the right phenotype that responds well. No onme tests your pheniotype so you don’t know. One phenotype actually sees cholesterol increase with fish oil. B vitamins can help lower elevated homocysteine levels. Vitamin D supplementation makes sense for true deficiency states. If only doctors could agree if it’s below 20 or 50? Magnesium may help with specific conditions like pregnancy complications, migraines, and muscle cramps. But here’s the thing: your primary care physician can order all of these tests, they’re typically covered by insurance, and your doctor can interpret the results in the context of your actual symptoms and medical history. 

For most other biomarkers? The story is very different. Elevated LDL cholesterol, apolipoprotein B (ApoB), and lipoprotein(a) are serious cardiovascular risk markers, but they’re not effectively treated with supplements. These require prescription medications like statins, lifestyle modifications such as diet and exercise, or in some cases have no proven interventions at all. Lp(a), for instance, is largely genetic, and no supplement is going to meaningfully change it. Throwing fish oil capsules at a high ApoB level instead of talking to your doctor about a statin isn’t just ineffective; it could delay treatment that actually works. 

And then there’s the safety issue. Supplements aren’t harmless just because they’re “natural” or sold without a prescription. They can interact with medications, worsen certain conditions, and cause problems you’d never anticipate. Vitamin E supplements increase bleeding risk, which is dangerous if you’re on blood thinners. High-dose vitamin A can cause liver damage. Iron supplements can be harmful if you don’t actually have iron deficiency. Calcium supplements may increase cardiovascular risk in some people. St. John’s Wort interferes with dozens of prescription medications, including birth control pills and antidepressants. 

When a DTC testing company recommends supplements based solely on your lab values, they don’t know what medications you’re taking. They don’t know about your kidney function, your liver health, or your family history. They don’t know if you’re pregnant or planning to be. They’re making recommendations without a full medical history, and that’s not just unhelpful; it’s potentially dangerous. 

So before you spend hundreds of dollars on supplements to “optimize” your biomarkers, ask yourself: Is there actual evidence this will make me healthier, or am I just trying to turn red numbers green? In most cases, you’d be better off saving that money for a gym membership or a few sessions with a registered dietitian. 

But Wait: Are There Any Benefits? 

In fairness, these services do offer some potential upsides. They’re convenient, with no doctor’s appointment required. They give people a sense of control over their health. And some users find the motivation helpful: if you can track your cholesterol over time, you might be more motivated to stick with healthy eating. 

Some specific biomarkers do have value for certain people. Tests like high-sensitivity C-reactive protein (hs-CRP) and NT-proBNP can help predict heart disease risk in people who already have risk factors. The American College of Cardiology has recommended hs-CRP screening, but in the context of proper medical evaluation, not as a standalone consumer product. 

The key difference is context. When a doctor orders a test, they’re considering your full health picture, your symptoms, your family history, and what they’ll actually do with the result. When you order 100 tests yourself, you’re fishing, and you might not like what you catch. 

What Actually Works: Evidence-Based Screening 

Medical organizations like the U.S. Preventive Services Task Force spend years studying which screening tests actually help people. Their recommendations are based on hard evidence from large trials. Only a handful of screenings have been proven to reduce death from disease: mammograms for breast cancer, colonoscopies for colorectal cancer, and a few others, each for specific age groups and risk levels. 

The screenings that work share something in common: they’ve been tested in rigorous studies that measured actual health outcomes, not just whether they found more diagnoses. Finding more stuff isn’t the goal. Finding stuff that, when treated, makes people healthier is the goal. 

If You Decide to Test Anyway: Get a Second Opinion 

Look, we get it. Some people are going to use these services no matter what the research says. Maybe you’re the type who likes having data. Maybe you have a family history that makes you nervous. Maybe you just want to feel like you’re doing something proactive. If you’ve weighed the costs and disadvantages and still choose to go ahead with comprehensive DTC testing, there’s one critical step you should take: don’t interpret those results alone. 

At minimum, run your test results through a service like Medome.ai to get a second opinion. Why does this matter? Because raw lab numbers mean almost nothing without context. A single “abnormal” value could be completely normal for you based on your age, sex, medications, recent meals, hydration status, time of day, and dozens of other factors. An AI system trained on medical data can help flag which results actually warrant attention and which are likely just statistical noise. 

More importantly, tools like Medome.ai can interpret your results within the context of your full medical history. That’s the piece that DTC testing companies typically miss. Your cholesterol numbers mean something very different if you’re a 25 year old marathon runner versus a 55 year old with diabetes and a family history of heart attacks. A slightly elevated liver enzyme could be meaningless, or it could be significant depending on whether you take certain medications or had a few drinks the night before your test. 

The goal isn’t to replace your doctor. The goal is to avoid the anxiety spiral that comes from staring at a dashboard full of yellow and red flags without knowing which ones actually matter. A second opinion, whether from an AI tool or a real physician, can help you separate the signal from the noise and decide which results, if any, are worth discussing with your healthcare provider. 

The Bottom Line 

Here’s the clear conclusion from the science: routine comprehensive blood biomarker testing in healthy people, the kind sold by companies like Function Health, has not been shown to make people live longer or healthier lives. The evidence shows these tests are more likely to cause harm through overdiagnosis, anxiety, and unnecessary follow-up procedures than to catch problems that would have been missed otherwise. 

If you’re feeling healthy and want to stay that way, the best approach is still the boring one: eat well, exercise, don’t smoke, limit alcohol, get enough sleep, and see your doctor for recommended age-appropriate screenings. It’s not as exciting as a dashboard full of 100+ biomarkers, but it’s what actually works. 

And if you do decide to test anyway? Don’t go it alone. Get your results interpreted by someone, or something, such as Medome.ai, that understands your full health picture. Skip the supplement upsells. And remember: more data isn’t always better data, but data with context is at least a step in the right direction. 

Sources and Further Reading 

• Krogsbøll LT, et al. “General health checks in adults for reducing morbidity and mortality from disease.” Cochrane Database of Systematic Reviews, 2019. 

• Schwartz LM, Woloshin S. “Medical Marketing in the United States, 1997-2016.” JAMA, 2018. 

• Kidd BA, et al. “Evaluation of Direct-to-Consumer Low-Volume Lab Tests in Healthy Adults.” Journal of Clinical Investigation, 2016. 

• Shih P, et al. “Direct-to-Consumer Tests Advertised Online in Australia: Systematic Online Review.” BMJ Open, 2023. 

• Ayala-Lopez N, Nichols JH. “Benefits and Risks of Direct-to-Consumer Testing.” Archives of Pathology & Laboratory Medicine, 2020. 

• Fiala C, et al. “Benefits and Harms of Wellness Initiatives.” Clinical Chemistry and Laboratory Medicine, 2019. 

• U.S. Preventive Services Task Force. Screening Recommendations. uspreventiveservicestaskforce.org