7 myths about blood testing (and what's actually true)

Your blood results come in, you spot one red arrow and your heart skips a beat. Sound familiar? Blood testing is surrounded by stubborn assumptions, and those are exactly what cause needless worry or false reassurance. A number next to a reference range says very little on its own.

That is why a doctor never looks at a single figure, but at the pattern and your story. At VitalCheck every result comes with a review by a BIG-registered doctor, for exactly that reason. Below we debunk the seven myths we run into most often, and explain what is actually true.

In short, these are the seven myths we debunk:

1. You always have to fast before a blood draw.
2. One abnormal value means something is wrong.
3. A normal result means you are completely healthy.
4. The more blood values you test, the better.
5. Within the reference range is automatically fine.
6. You will feel a vitamin deficiency or high cholesterol.
7. A blood test picks up almost everything.

Myth 1: you always have to fast before a blood draw

False. For most tests you do not need to fast. Fasting mainly matters for your fasting glucose and sometimes your blood lipids, because eating temporarily raises those values. For vitamins, thyroid and most hormones, a sandwich beforehand makes no difference.

What is true: always follow the advice for your specific test. In doubt, read when fasting is and is not needed in our article on fasting before a blood test.

Myth 2: one abnormal value means something is wrong

False. Reference ranges are set so that about five percent of healthy people fall just outside them by definition. Many values also fluctuate from day to day. One slightly abnormal result without symptoms is more often a reason to calmly repeat the test than to panic.

What is true: context determines the meaning. A value just outside the range in someone with symptoms calls for a different conclusion than the same value in someone without. That is why every VitalCheck result comes with a professional review.

Myth 3: a normal result means you are completely healthy

False. A blood test is a snapshot of a number of substances in your blood, not a full health scan. A reassuring result does not rule everything out. Many conditions, including early cancer and much of mental health, do not show up in your blood values.

What is true: a broad check gives a valuable picture of your main systems. Combine the result with your symptoms, your lifestyle and, in doubt, your GP's judgement.

Myth 4: the more blood values you test, the better

False. More markers do not automatically mean more insight. Both the Dutch College of General Practitioners and the Health Council point out that measuring many values without a clear reason often produces incidental findings, which lead to unnecessary follow-up and worry.

What is true: a targeted panel that fits your question is more useful than a list of forty random markers. Start broad with the basic health checkup, or go deeper with the extended health checkup.

Myth 5: within the reference range is automatically fine

False, or at least too simple. A reference range shows where most healthy people fall, not necessarily your personal optimum. A ferritin at the low end of the range can already drain your energy, even though you are technically within the norm.

What is true: your personal trend across several measurements often says more than a single snapshot. A value that drops every year tells a different story than a one-off low-normal result.

Myth 6: you will feel a vitamin deficiency or high cholesterol

False. Many abnormalities build up slowly and silently. A raised LDL cholesterol causes no symptoms for years, and a vitamin deficiency often starts with vague fatigue that you easily blame on something else.

What is true: precisely because you do not feel it, measuring is the only way to catch it in time. Read how to recognise a deficiency in our article on vitamin deficiency, or more about cholesterol.

Myth 7: a blood test picks up almost everything

False. Blood testing is powerful, but it has limits. It gives data on specific substances, not a ready-made diagnosis. Many conditions need additional investigation, and a blood test does not replace a visit to your GP when you have symptoms.

What is true: blood testing is excellent for following trends, spotting risks early and looking further in a targeted way. Want to start yourself without a referral? Read our complete guide.

Frequently asked questions

Do I need to fast for a blood test?

Usually not. Only certain values, such as fasting glucose and sometimes your blood lipids, require fasting. Follow the advice for your specific test.

Is one abnormal blood value a reason to worry?

Not necessarily. Many values fluctuate, and about five percent of healthy people fall just outside the range. The combination with your symptoms and the pattern over time weighs more than a single number.

How often is a blood test useful?

For healthy adults without symptoms, once every one to two years is a reasonable basis for following trends. With symptoms or risk factors, your doctor may advise more often.

In short: do not let one red arrow scare you, and do not expect more from a blood test than it can offer. The value lies in the pattern over time, in the combination with your symptoms and in a good interpretation. Every blood test result at VitalCheck includes a professional review by a BIG-registered doctor. A blood value is not a diagnosis: always discuss symptoms and treatment decisions with your GP.

Sources

• Dutch College of General Practitioners (NHG), on preventive blood testing without a specific reason.
• Health Council of the Netherlands (Gezondheidsraad), on caution in screening people without symptoms.
• RIVM, on the reliability of health tests.