Platelet Count

What is a platelet count?

A platelet count is a quick, common test that measures how many platelets are in your blood. Platelets, or thrombocytes, are tiny cell fragments that form clots when there’s damage to a blood vessel. For example, if you cut your finger, platelets mix with clotting factors (proteins in your blood). Together, they form a “glue” that stops the bleeding. There are tens of thousands of platelets in a single drop of blood.

A platelet count is usually part of a larger test called a complete blood count (CBC). This test measures the number of platelets, white blood cells and red blood cells in a blood sample. “PLT” is short for “platelets” on blood test results.

When is a platelet count needed?

Your healthcare provider may order a platelet count during a routine physical examination. They may do this test if they think you have:

• Thrombocytopenia (low platelet count).
• Thrombocytosis (high platelet count).

How does the test work?

A healthcare provider (typically a nurse or a phlebotomist) will collect a blood sample. Afterward, healthcare providers in a lab will test the sample to determine your platelet count.

How do I prepare for a platelet count?

Most people don’t need to do anything to prepare for a platelet count. If your provider plans on running other tests on the sample, they may ask you to fast (not eat or drink) beforehand.

Be sure to ask your provider if there are any instructions you should follow or medications to avoid before your blood test.

What happens during a platelet count?

Giving blood for a platelet count only takes a few minutes. You may get the test at your healthcare provider’s office, a hospital or a lab.

During your blood draw, a healthcare provider:

1. Selects a vein on the inside of your arm, near your elbow.
2. Places a tourniquet (tight band or cord) around your upper arm. (The tourniquet pushes blood down into your veins, making it easier to draw blood.)
3. Cleans the skin around your vein and inserts the needle. (You might feel a quick, light sting when the needle goes in.)
4. Fills a small collection tube with blood.
5. Removes the needle and tourniquet and applies a small bandage to your arm.

Some people feel nervous around needles or before having their blood drawn. It’s OK if you feel this way. Take deep breaths to relax. It may help to look away from the needle as the provider draws your blood.

What should I expect after the test?

The actual platelet counting (analysis) happens behind the scenes, after you’ve given blood. In a lab, a healthcare provider puts your blood sample in a small machine. The machine counts the platelets and other blood cells in about one minute.

In some cases, a healthcare provider may do a peripheral blood smear (PBS). This test examines a small sample of blood under a microscope. A blood smear assesses the size and shape of blood cells and platelets. Abnormal-looking cells may be a sign of certain conditions that a platelet count alone can’t detect. For example, some conditions involve both high or low platelet counts and other abnormalities, like giant platelets.

Are there any risks with a platelet count?

A platelet count is a simple, common test. There aren’t significant risks.

After the test, you may have light bleeding where the needle went into your vein. You might also see some light bruising or feel soreness on the inside of your arm. But these side effects typically disappear the same day of your blood draw.

What do platelet count results mean?

Platelet count results compare your number of platelets per microliter of blood to a reference range for a normal platelet count. Platelet counts outside of the normal range are considered “low” (thrombocytopenia) or “high” (thrombocytosis):

• Normal platelet count range: Between 150,000 and 400,000 platelets per microliter.
• Low platelet count (thrombocytopenia): Fewer than 150,000 platelets per microliter.
• High platelet count (thrombocytosis): More than 450,000 platelets per microliter.

If your platelet counts are outside of the normal range, you’ll likely need more tests to determine the cause. Lots of things can cause high or low platelet counts. Not all causes are serious or require treatment.

What if I have a low platelet count?

If your platelet count is low, you may not have enough platelets to clot a wound. If you’re injured, you may bleed too much. This could lead to excessive blood loss (hemorrhage) and internal bleeding, which is life-threatening.

But not everyone with low platelets experiences serious or long-term issues. In mild cases, you may not have symptoms at all. Much depends on what’s causing your low platelets and how low your count is. Some of the most common causes of low platelets are:

• Autoimmune diseases that destroy platelets.
• Cancers that slow platelet production or cancer treatments, like chemotherapy.
• Medication side effects.

What if I have a high platelet count?

If your platelet count is high, your platelets may stick together and cause unnecessary clotting in your blood vessels. Blood clots can lead to heart attack and stroke. Your risk depends on what’s causing high platelets.

Often, a high platelet count is temporary. For example, your body may make too many platelets in response to a certain situation that stresses your body, like surgery or an infection. If your provider suspects your high levels are short-term, they may test you again to see if your levels go down.

Some people are born with rare blood disorders that cause their bodies to make too many platelets. If this is the case, your provider will work with you to keep your platelet levels in a safe range.

When should I call my healthcare provider?

Contact your healthcare provider if you have questions about when you should expect results and/or what they mean.

Most people receive results as soon as that same day or within a few days of their blood draw. But you may need to wait up to a week for the lab to complete its analysis and share the results.

What is a normal platelet count by age?

A platelet count between 150,000 and 400,000 platelets per microliter of blood is considered normal, regardless of age. That’s a wide range, with lots of room for healthy variety. For example, it’s normal for platelet counts to decrease with age, especially after age 60. But decreased platelets that are still within the normal range don’t necessarily mean there’s a problem.

Your healthcare provider may choose to monitor your platelets more closely if they’re concerned that your counts are decreasing.

What level of platelets is concerning?

Whether or not you should be concerned depends on what’s causing the abnormal levels. Platelets outside of the normal range don’t necessarily mean you’re at immediate risk of blood loss or dangerous blood clots.

Having platelets below 50,000 per microliter of blood does increase your risk of bleeding even when you’re doing everyday activities. Your provider will monitor you closely if your platelets reach this level.