Causes
Heparin-induced thrombocytopenia are either formed as a non-immunological, harmless early form (type I) or are based on the formation of antibodies against platelet factor 4/heparin complex (type II). These cause the blood to clump together and the platelets are, so to speak, “caught away” or “trapped”, they can no longer perform their natural function.Unfractionated heparins have a higher risk of triggering HIT than, for example, Clexane, a low-molecular-weight fractionated heparin.
Symptoms
No symptoms usually occur in heparin-induced thrombocytopenia type I, the drop in platelets returns to normal spontaneously. Therefore, this type of thrombocytopenia usually proceeds in such a way that the affected person does not even notice it. The massive decrease in the number of platelets in type II heparin-induced thrombocytopenia often leads to pronounced symptoms of deficiency.
At the injection site of heparin, skin necrosis can be noticed, the skin turns a bluish-black color. It is an expression of cell death at this site. Due to the heparin-induced thrombocytopenia, the thrombocytes are activated and clump together, resulting in thromboses (clots) in the blood vessels.
As a result, the tissue to be treated can no longer be properly supplied with blood and nutrients from the blood and suffers massive damage as a result. If action is not taken in time, it may become necessary to amputate the affected limbs. If the thromboses manifest themselves in organs, strokes, heart attacks or a pulmonary embolism can occur, which are life-threatening. The spectrum of symptoms shows how dangerous heparin-induced thrombocytopenia type II can become.
Diagnostics
A heparin-induced thrombocytopenia is detected mainly in the blood count. There the drop in platelets can be measured. A drop of more than 50 percent is alarming; the values usually fall below 100,000 thrombocytes per microliter.
A more precise estimate of whether type II HIT is present can be made with the aid of the so-called 4 T-score. Important parameters here are the remaining number of thrombocytes (thrombocytopenia), the time elapsed between the start of heparin administration and the start of the drop-off (timing of drop-off), how serious the complications are, i.e. whether thrombosis, necrosis of the puncture site or other manifestations are present, and whether other possible causes of thrombocytopenia are considered. Zero to two points are awarded.
The higher the total number of points, the more likely the presence of heparin-induced thrombocytopenia type II is. New methods, the so-called ELISA or HIPA test, allow the detection of antibodies. A positive test result indicates a HIT with a simultaneous drop in platelets, whereas a negative test excludes it. In Germany, the HIPA test (Heparin-induced platelet activation assay) is mainly used.
