Thursday, October 21, 2010

What are Platelets?

Platelets, along with red cells and plasma, form a major proportion of both human and animal blood. Microscopically, they look like little thorned or spiky ovals, and they can only be viewed microscopically, as the average size is about four hundred thousandths of an inch (1 to 3.5 um).
Platelets are actually fragments of the cells in bone marrow, called megakaryocytes. Stimulated by the hormone thrombopoietin, platelets break off the megakaryocytes and enter the blood stream, where they circulate for about 10 days before ending their short lives in the spleen.

Normal Results
150,000 to 400,000 platelets per microliter (mcL)
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

According to some studies, almost 95% of healthy people have platelet values within this range. Even though a platelet count which is above or below this range is considered abnormal, some people with small variations are found to be perfectly healthy

Specifically, platelets provide the necessary hormones and proteins for coagulation. Collagen is released when the lining of a blood vessel is damaged. The platelet recognizes collagen and begins to work on coagulating the blood by forming a kind of stopper, so further damage to the blood vessel is prevented.

Bleeding in the skin may be the first sign that the platelet count is low. Often, many tiny red dots appear in the skin on the lower legs. People may bruise easily. Slight injuries sometimes cause small scattered bruises. The gums may bleed, and blood may appear in the stool or urine. Bleeding due to injuries may be hard to stop. Bleeding worsens as the platelet count decreases. When the count is below 20,000, bleeding in the digestive tract or brain may occur even when there is no injury. This bleeding may be life threatening.

A level which is below 50,000 or above 1,000,000 is considered as critical. In short, drastic variations in the normal platelet count can be considered as serious conditions, which have to be addressed as soon as possible. While these variations can be indications of diseases, serious health problems may also arise from such variations. As such, any variation in platelet count should be brought to the notice of a medical professional immediately.

A higher than normal count of platelets, known as thrombocytosis, can cause serious health risks. Too much clotting of the blood can lead to formation of blood clots that can cause stroke. Conversely, lower than normal counts can lead to extensive bleeding.

However, in some cases, inducing a lower platelet count is desirable, for instance if a person has susceptibility to strokes or has had extensive heart repair. Platelet counts can be lowered by a daily intake of aspirin or other clot reducing drugs. Additionally, when a patient has an intravenous drip (IV), heparin is used to keep the IV from clotting so fluids can be either taken from or added to the body.

While disease or a genetic disorder can cause a lower number of platelets, other times, they are depleted because of a specific treatment or surgery. Burn victims, organ transplant patients, marrow transplant patients, those undergoing chemotherapy, and those who have undergone heart surgery often require not only blood transfusions but platelet transfusions as well.

An infection of the hepatitis C virus and cirrhosis is another cause of low platelets. Most are familiar with the blood's ability to coagulate should one receive a cut or bruise. When the liver slows or stops producing the proteins needed for blood clotting, a person will bruise or bleed easily. Normally, blood from the intestines and spleen is carried to the liver through the portal vein. But cirrhosis slows the normal flow of blood, which increases the pressure in the portal vein. This condition is called portal hypertension. If your spleen enlarges due to cirrhosis of the liver or portal hypertension occurs, the spleen frequently holds white blood cells and platelets, reducing the numbers of these cells in the blood. A low platelet count may be the first evidence that a person has developed cirrhosis.

Spleen Geography 101:

A part of the lymphatic system, the dark purplish spleen lies in the upper left abdomen protected by the lower ribs. (Our unscientific, people-on-the-street survey suggests wide gaps in anatomy knowledge.

"Where is the spleen?" was met with, "Uh, it's somewhere in the main part of the body--not in the extremities.")

My, What a Fine Looking Spleen:

Size and weight can vary greatly, but in healthy adults the spleen is often about 5 inches long by 3 inches wide and 1 1/2 inches thick. A typical spleen weighs in at about 6 ounces in a healthy adult. But when it becomes enlarged--from malaria or other diseases--it can weigh a hefty 4 pounds or so.

They're Not Just for Venting:

Not that you've noticed, but the spleen is a busy little part. Its main tasks are to remove worn-out and damaged red blood cells and platelets and to help the body fight off infection.It filters foreign substances from the blood and produces white blood cells called lymphocytes, which help boost immunity.

Whose Spleen Is It, Anyway?

Spleens are handled by internists, though hematologists (physicians specializing in blood and blood-producing organs) and oncologists (physicians specializing in tumors) also provide spleen care, depending on the exact problem.

Spleens Gone Bad:

So what can go wrong with the spleen?

It can get too big, sometimes producing a soreness. Besides malaria, a host of other disorders are accompanied by enlargement of the spleen. A partial list:infectious mononucleosis, chronic liver problems, rheumatoid arthritis, lupus, the early stages of AIDS. In sickle cell anemia patients, the spleen enlarges and then patients lose spleen function, says Dr. Andrew Saxon, professor of medicine and chief of the division of clinical immunology at UCLA.

Patients with Gaucher's disease (a disorder of fat metabolism) have enlarged spleens, as do people with lymphomas and people with idiopathic thrombocytopenic purpura (ITP), a systemic illness marked by low platelet counts, weakness and anemia.The spleen can also get ruptured in car accidents, falls or stabbings.If the spleen is injured seriously, or otherwise causes too much trouble, it's likely to get yanked, although in some instances it is repaired.

Spleenless Wonders:

Yes, you can live a full life without your spleen.

About 1% of the population is spleenless, estimates Dr. Lawrence May, an internist at Encino-Tarzana Medical Center.Among the spleenless is talk show host Jay Leno. In his book "Leading With My Chin" (HarperCollins, 1996), he describes his childhood trip down the banister that ended at the hospital, where he and his spleen parted company.

Spleen Understudies:

The spleen's tasks are largely taken over by other parts of the lymphatic system and the liver. Oddly, some people--no one's quite sure how many--have a spare spleen. An accessory spleen, as it's known, is not rare, Saxon says.

Spleened Versus Spleenless:"On paper, spleenless is not as good as someone who has a spleen," Saxon says, referring to overall health. "They are more susceptible to infection," he says.

Those who have lost a spleen to rupture are generally healthier than those who are spleenless due to lymphoma, for instance, Saxon notes. Folks without a spleen should take some precautions, experts concur.

Among them:

Get vaccinated against pneumonia and always alert a new doctor or dentist to your condition. When fever strikes, people without a spleen can get sicker quicker, May says.And dentists may want to take extra precautions to minimize infection risks, says Dr. Eric Sung, a dentist and program director of the UCLA hospital dentistry program.People without spleens might also want to note that fact on a medical information bracelet.

Low platelet counts can usually be traced to one of the following:

Disorders that reduce platelet production by bone marrow: Various medical problems can affect bone marrow function, such as certain cancers, leukemia, bone marrow failure syndromes such as aplastic anemia, and some viral infections (such as HIV). Heavy alcohol use may also be a factor. There's also a long list of medications that can decrease platelet production. Since the chemical signal for the bone marrow to make platelets, thrombopoietin, is made in the liver, liver failure can also reduce platelet production.

Destruction of platelets: Several medical conditions are associated with premature loss of platelets from the circulation. These include immune system disorders such as lupus, rheumatoid arthritis, and idiopathic thrombocytopenic purpura (ITP), which occurs when antibodies mistakenly attack platelets.

There are also non-immune mechanisms for platelets to get destroyed, such as accelerated clotting due to cancer, or a loose-fitting mechanical heart valve.If the low count is due to an identifiable cause, treatment of that condition will usually result in improvement in the thrombocytopenia. Should the problem be related to an adverse drug effect, low platelet counts usually improve once medication changes are made as directed by your doctor.If the cause is ITP, treatment may include the use of corticosteroids, immune globulin infusions or medications -- such as cyclophosphamide

Many people with ITP do well without bleeding for many years despite a chronically low platelet count. A new class of drugs, romiplostim (Nplate) and eltrombopag (Promacta), act like thrombopoietin to stimulate increased bone marrow production of platelets. These new drugs may be useful in patients with ITP whose condition does not respond well to other treatments.Platelet concentrates may be given to help raise platelet numbers temporarily, especially if cancer or chemotherapy is related to the low count, or to prevent bleeding if you need surgery. Routine use of platelet transfusions may be limited by the formation of antibodies that can destroy new platelets. -- David Steensma, M.D., Hematology, Mayo Clinic, Rochester, Minn. / Mayo Clinic

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