You need to think of the clotting process hemostasis) as two different physiological processes. The formation of the platelet plug is one, the other is the fibrin clot. In this article, we will explore the platelet plug.
Now, there are two main problems with platelets, either 1) a decreased number or 2) bad (broken) platelets that have poor function. There are two tests that we need to evaluate for platelet function.
One is the platelet count as seen on the red blood cell count. So, we are looking at the absolute number, or we are looking at a test called the bleeding time. When a platelet count is decreased, this is known as thrombocytopenia. This is seen if there is a problem in the bone marrow such as decreased production of platelets which you can see in some malignancies, most commonly seen in chemotherapy that suppresses bone marrow, increased destruction such as a hyperactive spleen where the only potential solution to this is to have a splenectomy, or from idiopathic thrombocytopenia which is typically a child after a viral syndrome where the treatment is steroid removal immunoglobulin or spleen removal. When I was in my pediatric rotation, I remember seeing a young child for a well child visit, and this was actually my first rotation as a physician assistant student. When the physician came in, the child clearly responded adversely to the pediatrician who was a bit older with a beard, and the mom said that he looked kind of like his father. The child was really kind of frightful of the physician. When he looked over the child, the child had a number of bruises especially on his lower legs. I believed this child was being abused by his father. The doctor sent him off for blood work, and I was quite upset with the physician which I talked about wondering how he could not see how apparent abuse was. Well, when the blood work came back, this child had idiopathic thrombocytopenia, and it was not child abuse.
Sepsis, in the setting of a low platelet count, is a red flag for a patient requiring intensive care. If the platelet count is less then 50K, they have an increased risk of post traumatic bleeding. If you have platelet counts of less than 20,000, you can have increased spontaneous bleeding. It was common to transfuse platelets in a patient when their count falls below 10K.
The bleeding time is a test of platelet function. The bleeding time is a small abrasion in the skin, and the time it takes to stop is a measure known as bleeding time. I may have only ordered this test once in my life. It is pretty rare. The most common reason why platelets would not clot well is aspirin, someone who takes aspirin, their blood is a little bit thin. Or uremia. Hypothermia can do this as well.
The lifespan of a platelet is 7 days. Aspirin deactivated the platelet for that length of time. We will exclude genetic coagulopathies here. But, I do want to talk about medications that affect the platelets. The most common one by far is aspirin. The dose can vary between 81 mg to 1,000 mg daily. Plavix is typically 75 mg once per day, and has been used with success in people with known coronary artery disease or atherosclerotic disease such as a past myocardial infarction or stroke. GB 2B/#a inhibitors are used in ACS. It is kind of like a fancy IV aspirin.