In laboratory medicine, reference intervals play a central role when it comes to evaluating laboratory results and assessing a person’s health.

What are reference intervals?

A reference interval is a range of values that indicates what is considered “normal” for a particular laboratory value – for example blood sugar, cholesterol or red blood cells – in healthy people. This range is usually defined so that it covers 95% of the values of a healthy comparison group. This means that if a laboratory value is within this range, it is usually a sign that everything is in order. If it is above or below this range, this could indicate a health problem – although not necessarily, as we will come to later.

Think of the reference interval as a kind of guide: It’s a benchmark that doctors can use to compare your values to see if anything is abnormal. For example, the reference interval for blood glucose could be 70 to 100 mg/dl. If your value is 85, it fits into the “normal” range. If it is 120, it is higher and could be an indication of diabetes.

How are reference intervals determined?

Reference intervals are not simply made up – they are based on extensive examinations. Many healthy people are tested and their laboratory values are collected and analyzed. It is important that this reference group matches the person being tested as closely as possible. This is because factors such as age, gender, lifestyle or even origin can have an influence on the values. This is why there are often different reference intervals, for example for children, adults or pregnant women.

The scientists then look at how the values are distributed in this group and define the range so that the middle 95% are included. The remaining 5% – i.e. values that lie just outside this range – are not automatically “ill”, but are simply less common.

Why are reference intervals so important?

Reference intervals help doctors to classify laboratory results correctly. Without this benchmark, it would be difficult to say whether a value is “good” or “bad”. They are, so to speak, the compass in laboratory medicine. For example, if your cholesterol value is 250 mg/dl and the reference interval ends at 120 to 200 mg/dl, the doctor knows that there could be a risk of cardiovascular problems.

However, a value outside the interval does not automatically mean that you are ill. It is just an indication that needs to be investigated further. Some people naturally have values that are outside the range without there being a problem. The time of day, food or stress can also influence values. That’s why a doctor never just looks at the lab slip, but looks at the whole picture: your symptoms, your life circumstances and other examinations.

What reference intervals cannot do

Reference intervals are not a panacea. They are a guide, but not an absolute truth. For one thing, they can vary slightly depending on the laboratory because different devices or methods are used. Secondly, they are designed for average values – and not everyone fits into this average. A professional athlete may have different “normal” values than someone who does little sport. Diseases do not always show up immediately in the laboratory either: a value can be “normal” even though something is wrong.

Conclusion

Reference intervals are an indispensable tool in laboratory medicine. They give doctors a clear basis for evaluating laboratory values and identifying potential problems. At the same time, they are only one piece of the puzzle – the exact diagnosis only emerges through discussion and further examinations. For us patients, it is reassuring to know that these guidelines exist to help us keep an eye on our health. So the next time you have a lab report in your hands, take a look at the reference values – they tell you more than you might think at first glance!

Matching:

Vision loss and high cholesterol levels identified as dementia risk factors – MedLabPortal

Cholesterol-lowering drugs: What you should do if you have symptoms – MedLabPortal

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Gender note. The personal designations used in this text always refer equally to female, male and diverse persons. Double/triple references and gendered designations are avoided for the sake of better readability ected.