The thromboplastin time, often referred to as the “quick value” or “prothrombin time” (PT), is an important test in medicine that shows how well the blood clots. It measures how quickly the blood turns into a solid clot after the addition of certain substances. This is particularly important to check whether blood clotting is functioning normally – for example in people taking medication such as Marcumar, in the case of liver disease or before operations. In Germany, this test is a standard procedure in laboratory medicine and is carried out daily in doctors’ surgeries, hospitals and laboratories.

Why is the thromboplastin time important?

Blood clotting is a complicated process in which various proteins – known as clotting factors – work together to stop bleeding. The thromboplastin time primarily checks the so-called “external coagulation pathway” and the “common pathway”, i.e. certain sections of this system. These include factors that are produced in the liver and for which vitamin K plays a role. If these factors are not working properly – for example due to liver disease, vitamin K deficiency or medication that affects coagulation – it takes longer for the blood to clot. This can be determined using the thromboplastin time.

How is the thromboplastin time measured?

In Germany, the determination of the thromboplastin time in the laboratory usually follows a standardized principle. First, blood is taken from the patient, usually from a vein in the arm. This blood is placed in a tube containing a substance called citrate, which prevents it from clotting before the test. The tube is then sent to the laboratory.

The blood plasma – i.e. the liquid part of the blood without cells – is prepared in the laboratory. To do this, the blood is rotated in a centrifuge until the solid components settle out. Now comes the actual test: a mixture of thromboplastin and calcium is added to the plasma. Thromboplastin is a substance that triggers clotting, and calcium helps with this because it is necessary for the reaction. A device then measures how many seconds it takes for the plasma to clot. This device, known as a coagulometer, detects the change automatically, for example by light or mechanical measurement.

The Quick value and the INR value

The results of the thromboplastin time are often given in two forms in Germany: as a Quick value (as a percentage) or as an INR (International Normalized Ratio). The Quick value compares the patient’s clotting time with that of a healthy person. A value of 100 % means that clotting is normal, while a lower value (e.g. 20 %) indicates that the blood is clotting more slowly. The INR value is an international standard value that is mainly used for patients on blood thinners such as Marcumar. The following applies here: an INR of 1 is normal, values between 2 and 3 are often the target for anticoagulant therapies.

What influences the thromboplastin time?

The results can be changed by various things. Medications such as Marcumar or heparin make the clotting time longer because they influence the clotting factors. Diseases such as liver cirrhosis can also change the value, as the liver produces fewer coagulation factors. Even diet plays a role: people who eat little vitamin K – for example due to a one-sided diet – can also have abnormal values because vitamin K is important for the factors.

Quality and standards in Germany

Laboratory medicine is very strictly regulated in Germany. Laboratories must adhere to strict guidelines, for example the guidelines of the German Medical Association. In addition, the thromboplastin time is often measured using standardized reagents (test substances) so that the results are comparable – regardless of whether the test is carried out in Munich or Hamburg. Many laboratories also use the INR value because it is internationally standardized and doctors can work with it worldwide.

Conclusion

The thromboplastin time is a simple but extremely useful test to check blood clotting. In Germany, it is carried out in the laboratory using modern technology and clear standards – from blood collection to evaluation. For patients, it means safety, for example when checking medication or diagnosing illnesses. Even if the details sound complicated, the idea behind it is simple: it is about understanding how quickly the blood can clot to protect the body.

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