Vitamin K is an inconspicuous but vital vitamin that plays a key role in the body – especially when it comes to blood clotting. It ensures that wounds can close and bleeding can stop. Vitamin K is therefore a recurring topic in laboratory medicine, for example in tests such as the thromboplastin time or in patients with certain diseases.

What is vitamin K?

Vitamin K is a fat-soluble vitamin, which means that it is absorbed and stored in the body with the help of fat, especially in the liver. There are different forms: Vitamin K1 (phylloquinone) comes from plants such as green vegetables – spinach, broccoli or kale are real vitamin K bombs. Vitamin K2 (menaquinone) is produced by bacteria, for example in fermented foods such as cheese or sauerkraut, but also by our own intestinal bacteria. Both forms are important for the body, especially for blood clotting.

The role in blood clotting

The main function of vitamin K is to help the liver produce certain proteins called clotting factors. These include factors II (prothrombin), V, VII, IX and X – names that sound complicated, but simply put ensure that blood clots when it needs to. Vitamin K activates these factors by chemically modifying them. Without this vitamin, they would not be able to do their job and the blood would simply continue to flow in the event of injury. That would be life-threatening.

Why vitamin K is important in laboratory medicine

In laboratory medicine, vitamin K is often looked at indirectly, namely via tests such as the thromboplastin time or the Quick value. These tests measure how quickly the blood clots, and this depends directly on the clotting factors that vitamin K needs. If someone has too little vitamin K – for example due to a poor diet, illness or medication – clotting takes longer. This is then reflected in the laboratory values: the Quick value falls and the INR value rises. Doctors can thus recognize whether there is a vitamin K deficiency or whether something else is interfering with coagulation.

What influences the vitamin K level?

Vitamin K levels in the body can fluctuate due to various things. Diet is a big factor: if you hardly eat any green vegetables, you risk a deficiency. Diseases also play a role. In the case of liver problems, such as cirrhosis, the body cannot use vitamin K properly because the liver no longer produces the clotting factors well. Intestinal diseases, such as Crohn’s disease, can interfere with the absorption of vitamin K. And then there are medications: Blood thinners such as Marcumar (a so-called vitamin K antagonist) deliberately block the effect of vitamin K in order to slow down clotting. This is done in patients at risk of thrombosis, but must be closely monitored in the laboratory.

Vitamin K in everyday laboratory work

In Germany, vitamin K itself is not often measured directly – that would be complicated and expensive. Instead, people look at the coagulation tests to draw conclusions. If the thromboplastin time is prolonged and there are no other causes such as medication, this could be due to a vitamin K deficiency. In such cases, the doctor can administer vitamin K, for example as an injection or tablet, and then check whether the values improve. This is a simple trick to test whether the vitamin is really missing.

Special cases: Newborns and vitamin K

Newborn babies are an exciting example from laboratory medicine. Babies are born with very little vitamin K because it hardly reaches the mother via the placenta and their intestinal bacteria do not yet produce enough K2. As a result, they may initially have problems with blood clotting, which would show up in laboratory values. In Germany, newborns are therefore given vitamin K immediately after birth as a prophylaxis to prevent dangerous bleeding – a small intervention with a big effect.

Conclusion

Vitamin K may seem inconspicuous, but without it nothing works when it comes to blood clotting. In laboratory medicine, it helps doctors to identify and treat problems such as deficiencies, liver disease or the effects of medication. It is not measured directly, but is revealed via the coagulation values – a bit like a detective working in the background. Whether through spinach on the plate or an injection in hospital, this vitamin ensures that our blood coagulates at the right moment – and laboratory medicine helps to keep an eye on this.

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