A blood transfusion can be a life-saving intervention if you’ve lost a lot of blood due to illness or injury, but there are some limits. How many blood transfusions you can safely have depends on your condition.

There aren’t any guidelines currently for how many blood transfusions you can receive if you have a chronic condition or in an emergency. However, research has given doctors a good idea of who can benefit from a blood transfusion and whether there’s a limit to the amount of blood that should be used in each transfusion.

Many hospitals have policies regarding how low your blood cell counts must be before you may need a blood transfusion. These policies are often known as transfusion parameters.

Research has shown that restricting blood transfusions until a person has a hemoglobin level between 7 and 8 grams per deciliter (g/dL) is associated with reduced mortality, shorter hospital stays, and greater recovery. Another study found that restricting transfusions to the 7 to 8 g/dL parameter led to better outcomes as well as reduced costs.

You may require a blood transfusion after surgery, particularly when a surgeon has to make an incision and operate on an area that has a lot of blood flow. If your surgeon knows you may lose a lot of blood, they may request that you are “typed and crossed” before the procedure. This means blood bank professionals will test your blood for its type and crossmatch it to ensure it’s compatible with blood from a donor. Surgeons often ask for blood to be “on hold” or even available in the operating room.

Some medical conditions can result in chronically low blood counts. This includes acute kidney failure and cancers, especially when you’re receiving radiation or chemotherapy. In these cases, your doctors will expect you to have lower blood counts. They may be less likely to recommend a blood transfusion because your body is accustomed to a lower blood count.

Blood transfusions can be limited for a number of reasons aimed at keeping you safe. Blood is preserved with a compound called citrate to keep it from clotting. Exposure to citrate from repeated transfusions in a short amount of time can cause your potassium levels to go very high, while your calcium and magnesium levels dip. All of these changes can affect your heart.

Administering a massive transfusion is associated with a number of potential complications. A massive transfusion is classified as more than 4 units of packed red blood cells in an hour, or more than 10 units of packed red cells in 24 hours. This is enough blood to replace an average-sized person’s entire blood volume. Potential complications include:

  • electrolyte abnormalities
  • hypothermia (low body temperature)
  • blood that clots excessively or not enough
  • metabolic acidosis, in which your bodily fluids contain too much acid
  • air embolism, or air introduced into your veins that could cause a stroke or heart attack

Massive transfusions are usually given:

There aren’t guidelines as to the maximum number of blood products a doctor will give a person who is severely bleeding. However, research has shown the more blood given, the less likely a good outcome.

While doctors don’t limit the number of blood transfusions over a person’s lifetime, having to get a lot of blood in a short amount of time can result in greater risk for side effects. This is why doctors rely on transfusion parameters to decide when to use a blood transfusion.