Thursday, September 23, 2010

3.3f Blood Clot, Platelets & Spleen

Physician's Notebooks 3  - - See Homepage
3f Continues Chapter 3, Notebooks 3: Platelets, Clotting, Spleen
The Blood Platelets or Thrombocytes
Update 25 November 2018

The platelets when disrupted initiate a chemical reaction in blood plasma that starts with the platelets' being attracted (aggregated) to breaks inside blood vessel walls. The attraction to roughened but intact inner artery is important in narrowing and blocking the arteries, ie, atherosclerosisIt starts a clotting reaction in the blood serum of 3 substances: 1) prothrombin a pro clot agent made in the liver from vitamin K; 2) a pro clot, anti-heparin factor; and 3) the calcium ion (Ca2+), which has an affect on blood clotting. 
   Aspirin in as low a dose as 30 mg a day disables the platelets' aggregating power sufficiently to slow the blood clot and speed its dissolution, so aspirin or like platelet-aggregation medications (clopidogrel, plavex) are popular, in a range of doses, in daily use to prevent blood clots and thrombotic strokes and myocardial infarction heart attacks and, possibly to slow the atherosclerotic process. But aspirin is also a risk for bleeding.
   Now let us consider the blood clot? Even when clotting is prompt, hemorrhage is possible because the clot, which acts to plug holes or tears in blood vessels, may break up and dissolve too quickly. Clot retraction in 6 to 10 minutes in test tube sample of freshly drawn blood is a useful, easy test to show adequate clot retention with time.
   The blood platelet is one quarter size of the RBC. It is squeezed off from the cell substance of a bone marrow cell and it circulates in blood for c.10 days. The normal platelet count is 150- to 450-thousand platelets per micro-Liter (cu. mm) blood. High platelet count is a cause of a hyper-coagulation state. (Shown by clotting in 5 minutes or less) and leads to stroke or heart attack. 
   When platelet count goes too low or if normal platelet count shows inability to prolong the clot, a hemorrhagic hypo-coagulation state exists. It may be from aspirin. Ideally, you should not take any drug within 72 hrs before testing for blood clotting.

The Role of Spleen in Blood Clotting: The spleen is a liver-like organ located under the ribs on your left side. Normally it cannot be felt by a doctor but after it doubles in size it can be felt and as it further enlarges it starts to bulge out the left upper abdomen and causes a dull pain made worse by coughing or at end of a deep breath. The spleen filters out and destroys old, damaged or abnormally shaped platelets, and old white and red blood cells. One who is either born without spleen or lost it surgically can live fairly well but at risk for blood clot in vein or artery that leads to emboli to lung or brain. Platelet count with no spleen is high (c.1 million). Another important effect of not having a spleen is loss of immunity to capsular cocci bacterial infections like pneumococci; so anyone without a spleen ought to have pneumovax immunization and access to good antibacterial antibiotic. In leukemia cases, immunoglobulin shots may be given.

When the spleen works excessively, in hyperimmune disease and leukemia, the platelets are low or function poorly and hemorrhage is a risk. Also the red blood cells are destroyed more rapidly by trapping or hemolysis. Result is anemia worsened by poor clotting hemorrhage risk.

Blood clot tests: Following is a Yes-No testing for simple observation of blood clotting in a tube: Does the blood sample clot within 6 to 15 minutes or not? Answer Yes, suggests normal initial clotting mechanism. But it still leaves out the clot's dissolving too fast because of platelet abnormality, so it leads to further question: Does clot contract and retract or not after one hour? The answer Yes, means normal clotting mechanism with normal platelet count and function but a No means platelet abnormality (either too low count or abnormality of function with normal platelet count). With the two opposites - either too quick or too slow clotting - by using the internet we may access a diagnostic list that tells us the diseases of too fast clotting or too slow clotting.  A No answer to the clot retraction test calls for a platelet count and microscopic analysis of platelet structure and may lead to diagnostic categories like coagulation factor diseases, bone marrow diseases or leukemia.

 Dealing with High and Low Platelet Counts  A high platelet count is almost always due a lack of spleen function, either from a splenectomy or damaged spleen. The count is 1 million or so and usually stays that way for life. I have experience with a patient like that and after 10 years now, no problems with abnormal blood clotting. Often doctors advise low dose daily aspirin to lower the risk of internal blood clot. Precautions against clotting are to be well hydrated by drinking lots of water and not get your body into a cramped position - like on an intercontinental jet - sitting too cramped, too long; get up and stroll the aisle frequently.
   Low platelet counts, or thrombocytopenia are more frequent than high. Although 150,000 is lower limit of normal we can tolerate down to 20,000 with no major hemorrhage, assuming we do not have surgery or trauma accident or bleeding GI ulcer. Below 20,000 needs platelet transfusions. If the cause is auto-immune or if it's a case of benign idiopathic thrombocytopenia (ITP), usually in kids, corticosteroids are often given for counts below 30,000 but that should be temporary treatment because of steroid side effects.
Tests of Abnormal Blood Clotting in Vein or Artery: The best blood test is D-dimer. If the D-dimer is negative it rules out deep vein thrombosis (DVT), pulmonary embolus, thrombotic stroke. When D-dimer is positive, with swelling and pain in calf muscle it confirms a diagnosis of DVT and calls for rapid anti-coagulation medicine. The D-dimer is reported as micrograms per ml (fibrinogen equivalent units, ) or ng (nanograms) per ml D-Dimer Units (DDU) of blood serum.
   Another important test of blood clotting is the INR (international normalized ratio). It is a measure of the vitamin K effect on assisting blood clotting and is used on all patients who take the anti-vitamin K coumadin, or Warfarin after a DVT or in atrial fibrillation. It monitors the anticoagulant (anti-clot) effect of the medicine and usually done once a week. Now there are good self testers. Using coumadin, an INR between 2 and 3 units is aimed for and generally achieved with 5 mg coumadin a day. Normal INR without medication should be 1 unit unless liver function is poor.

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