Serum is the liquid part of the blood that remains when the solid components such as red and white blood cells and clotting factors are removed. Think of blood like a soup: The cells are the deposits, and the serum is the clear broth around them. It makes up about half of the blood and contains water, proteins, salts, sugar, hormones and many other substances that circulate in the body. Unlike “plasma” – a similar term – serum does not contain any clotting substances such as fibrinogen because these fall out during the extraction process.

Serum is something like a mirror of the body: it shows how well organs such as the liver or kidneys are working, whether inflammation is present or whether important substances such as sugar or cholesterol are in balance. It is therefore a treasure trove of information for doctors.

How is serum obtained?

In Germany, the whole process is carried out by laboratory medicine – i.e. special laboratories that work with precise technology. It all starts with a blood sample, usually taken by a GP or in a practice. Blood is taken from the vein, often in a tube without additives or with a coagulation aid. The blood must then first “clot” – that is, the solid parts clump together. This takes around 20 to 30 minutes. A centrifuge then comes into play: the tube is rotated quickly so that the heavy cells settle at the bottom and the clear serum remains at the top. This serum is then aspirated and is ready for analysis.

Why is serum so important for laboratory medicine?

Serum is the star in laboratory medicine because it reveals so much about health – and without interfering cells that could falsify the measurement. Laboratories can determine hundreds of values with serum, for example:

• Liver values (such as ALT or GGT): tell you whether your liver is healthy or whether you have a fatty liver.
• Kidney values (such as creatinine): Check how well the kidneys are filtering.
• Cholesterol: Measures the risk of heart problems.
• Inflammation values (such as CRP): show whether something is burning somewhere in the body.

The list is long and the tests are usually carried out automatically using modern equipment. These machines measure how certain substances in the serum react to light or chemicals and display the values in units such as milligrams per deciliter (mg/dl) or millimoles per liter (mmol/l). In Germany, there are clear limits for many values – such as blood sugar, which should be below 100 mg/dl on an empty stomach. But the doctor always looks at the overall picture, because every person is a little different.

How does this work in Germany?

The process is well organized: The doctor sends the blood to the laboratory – often directly from the practice or via a laboratory service. There, the serum is precisely prepared and analyzed. The results are sent back to the doctor, who discusses them with the patient. If the values are conspicuous, tips such as dietary changes or medication follow – or further tests if something is unclear. Health insurance companies usually pay for such analyses, for example for routine checks from the age of 35 or if symptoms occur.

Laboratories in Germany must adhere to strict rules to ensure that the results are reliable. This means that the equipment is tested regularly and the employees are highly trained. This ensures that a test in Hamburg is just as accurate as one in Stuttgart.

Why serum and not whole blood?

Why not just take the whole blood? Because the cells and clotting substances could interfere with the measurements. Serum is clear and “clean”, so the devices measure exactly what they are supposed to. For some tests, such as blood group or blood cell count, you do need whole blood – but for most metabolic and organ values, serum is the best choice.

Conclusion: Serum as a health detective

Serum is like a window into the body – it shows what’s going on inside without you having to do much searching. In Germany, laboratory medicine makes this possible: the serum is obtained with a small blood test and provides answers to questions about health. Whether liver, kidneys or heart – serum helps to detect and treat problems at an early stage. If you are curious about your values, you should talk to your doctor – a simple test can provide a lot of clarity and protect your health.

Editorial office: X-Press Journalistenbüro GbR

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.