Understanding Low Platelets

Quick summary

Think of platelets in the same way you'd think of cornstarch or flour when you mix it in a sauce or stew, and it's easy to see why they're so important: They're the clotting factors that make blood thicken and harden. Without them, bleeding becomes unstoppable and suddenly every minor cut or injury becomes dangerous.

Why does cancer make platelet counts drop?

In most cases, it's not the cancer itself but the treatment that causes low platelets . Chemotherapy can make platelet counts fall because it targets cells that grow rapidly. Tumor cells grow and divide quickly, but so do the cells in the bone marrow that produce red blood cells and platelets. Radiation can also cause a low platelet count (also called thrombocytopenia), especially radiation to the pelvic area, because there's a higher proportion of bone marrow in the pelvic bones. But some cancers, particularly lymphoma and leukemia, can lower platelet production if they spread to the bone marrow.

Can low platelet counts be prevented?

There are medications called cell growth factors that can be given along with chemo or radiation to prevent blood counts from dropping. The growth factor that works for low platelets is called oprelvekin (brand name Neumega). There's a risk of side effects with this medication, though, so the doctor will decide whether to prescribe it based on her assessment of the patient's risk of developing a low platelet count. The doctor will also consider whether he has heart problems, because Neumega's side effects include fluid retention and heart palpitations -- both of which can worsen heart conditions. Other side effects include diarrhea and other digestive issues.

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How long will it take platelet counts to rise again?

That's the big question, and the answer is: probably within three to four weeks. Doctors can't make an accurate prediction because platelet count depends on many factors, including the type of cancer, type of treatment -- particularly the type and dosage of chemo -- and a patient's general state of health. One thing to keep in mind is that a patient's platelet count generally won't drop immediately after chemo; it usually takes a week or two. This is because chemo doesn't kill off the platelets already in the bloodstream, which are mature and aren't dividing rapidly. It kills off the cells forming in the marrow, and therefore there's a delayed response, with the lowest platelet counts (called the nadir) usually occurring seven to 14 days after chemo.

After that, a patient's body will begin regenerating platelets at a rate of approximately 10 percent a day. (Platelets have a life span of eight to ten days, so, on any given day, approximately 10 percent are being lost and replaced.) But some types of cancer and some types of trea tment suppress the production of platelets, so the rebuilding process can be much slower.

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How low do platelet counts need to go before treatment is necessary?

The answer to this question, in most cases, depends on whether the patient is having bleeding problems, because most doctors will treat the symptoms rather than looking only at the platelet count. A normal platelet count is between 150,000 and 450,000 per cubic millimeter, but most people won't experience serious bleeding problems until their platelet count drops below 50,000, and some will function fine with a platelet count lower than that. "Doctors try not to treat to a number because everyone is different and reacts differently," says Andrew Putnam, director of the Palliative Care program at Lombardi Comprehensive Cancer Center and Georgetown University. "If you aren't having problems with bleeding, then the doctor will probably let it go lower and see if the counts recover."

What symptoms of low platelet count should I watch for?

Bruising and bleeding that won't stop are the two main signs of a low platelet count. A patient may have frequent nosebleeds or a nosebleed that won't stop. Women who are still menstruating need to watch out for heavy flow that seems like it won't let up. Less common symptoms of a low platelet count are blood in the stool or black, tarlike stools; blood in the urine; or a skin rash of pinprick-size red dots.

If there haven't been any problems with excessive bruising or bleeding, the doctor will probably wait to treat it, but there are still protective steps you should take.