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Blood transfusion is typically recommended when hemoglobin levels reach 70 g/L (7 g/dL) in those who have stable vital signs. For those with heart disease it is recommended at 80g/L (8 g/dL).

RBCs are used to restore oxygen-carrying capacity in people with anaemia due to trauma or other medical problems, and are by far the most common blood component used in transfusion medicine. Historically they were transfused as part of whole blood, are now typically used separately as RBCs and plasma components. The process of identifying a compatible blood product for transfusion is complicated.

High red blood cell count may be caused by low oxygen levels, kidney disease or other problems.

Low oxygen levels

Your body may increase red blood cell production to compensate for any condition that results in low oxygen levels, including:

• Heart disease (such as congenital heart disease in adults)
• Heart failure
• A condition present at birth that reduces the oxygen-carrying capacity of red blood cells (hemoglobinopathy)
• High altitudes
• COPD (chronic obstructive pulmonary disease)
• Pulmonary fibrosis (scarred and damaged lungs)
• Other lung diseases
• Sleep apnea
• Nicotine dependence (smoking)

Performance-enhancing drugs

Certain drugs stimulate the production of red blood cells, including:

• Anabolic steroids
• Blood doping (transfusion)
• Injections of a protein (erythropoietin) that enhances red blood cell production

Increased red blood cell concentration

• Dehydration (If the liquid component of the blood (plasma) is decreased, as in dehydration, the red blood cell count increases. This is due to the red blood cells becoming more concentrated. The actual number of red blood cells stays the same.)

Kidney disease

Rarely, in some kidney cancers and sometimes after kidney transplants, the kidneys might produce too much erythropoietin. This enhances red blood cell production.

Bone marrow overproduction

• Polycythemia vera
• Other myeloproliferative disorders
  

Extensive testing is done to prevent tainted blood from reaching the blood supply. An initial screening is done to make sure the donor has no medical conditions or high-risk behaviors that make blood donation unwise. The donor is also screened for current illnesses, such as having a cold or the flu or having an infection (a risk for spreading an infection to the recipient). Once the blood has been collected, it is tested for infectious diseases, including hepatitis and HIV.

The blood supply in the United States is among the safest in the world, however, if you are in a country outside of the US, the level of safety may vary widely. Abroad, you may have difficulty obtaining a blood transfusion (limited supply), the supply may not be considered safe, or testing may not be adequate.

Whole blood is not typically transfused, instead, the component the patient needs is given. The patient may receive plasma, or packed red blood cells, or if there is a need both may be given.

After donated blood is collected, the components are separated in a centrifuge, then a small amount of an anticoagulant is added to keep the packed red blood cells from clotting. The blood is kept in a refrigerator and is good for approximately 42 days from the date of donation.

PRBCs must be matched to the recipient, meaning that the blood type of the donor and the recipient must be compatible. If the blood is not properly matched, the result can be a life-threatening reaction, so the match is typically double checked by lab staff and nursing staff at the minimum.

Approximately one in seven hospitalized patients needs a transfusion. The chances of needing a transfusion are higher when having surgery, and you may be told prior to the procedure that you will require blood. Some patients prefer to avoid a transfusion when possible or have religious beliefs that forbid transfusions. For this reason, bloodless surgery, a group of techniques that help patients avoid or minimize the need for blood is often performed for these patients.