The Components of Blood

The components of blood are frequently used for transfusion, separately in different medical conditions. Many times whole blood may not be indicated and one component is sufficient for treating the patient.

Packed Cell Volume (PCV)

  • Among the components of blood, Packed Cell Volume is the most important and commonly transfused component.
  • These are used when volume replacement is not necessary like in anemic patients.
  • Haematocrit of PCV is 70%.
  • Volume of PCV is 250 ml.
  • 1 unit of PCV raises hemoglobin by 1.5 to 2 g%.
  • The half life of transfused RBCs is less (60 days).
  • These are to be diluted in normal saline before infusion.

The advantages of packed cells are:

  • Infectious and allergic problems related to plasma can be avoided.
  • Cardiac overload due to whole blood can be avoided.

Frozen RBCs

These are expensive but the chances of reaction and disease transmission are very low.

The frozen RBCs can be stored for years. Intercellular 2,3 DPG can be retained for years in frozen RBCs.

Fresh Frozen Plasma (FFP)

  • In FFP, plasma is frozen within 6 hours of collection.
  • Volume is 225 ml.
  • FFP contains all coagulation factors and plasma proteins among all the components of blood.

Indications

  • Treatment of coagulopathies associated with liver diseases, blood transfusion.
  • Reversal of warfarin therapy.
  • Antithrombin III deficiency.
  • Plasma protein deficiency (fresh frozen plasma is poor man’s albumin).
  • Each unit of FFP increases the level of each clotting factor by 2 to 3%.
  • ABO compatibility with FFP may not be necessary but desirable.

Platelet Concentrates

  • Volume: 50 ml.
  • Platelets are the only among the components of blood which are stored at room temperature. Survival at room temperature is 4 to 5 days while at 4°C it is 24 to 48 hours.
  • 1 unit of platelet increases the count by 5,000- 10,000.
  • Count < 50,000 are associated with increased blood loss during surgery so these patients should be given platelets preoperatively to increase the count to 1,00,000 before accepting for surgery.
  • Transfused platelets generally survive for 2 to 7 days following transfusion.
  • ABO compatibility is desirable but not necessary (if large numbers of platelets are to be given then ABO compatibility becomes necessary).

Cryoprecipitate

Volume: 10 mI.

1 unit of cryoprecipitate contains 80 to 145 units, factor VIII and 250mg of fibrinogen. Cryoprecipitate also contains factor XIII and Von Willebrand’s factor. Cryoprecipitate is pooled from many donors so there is maximum chance of disease transmission among all the components of blood.  Better pre-donor screening and availability of newer methods of testing have virtually eliminated the risk of disease transmission with cryoprecipitate in western countries.

Granulocyte Precipitate

The Granulocyte Precipitate is the preferred among the components of blood for neutropenic patients.

Thus in clinical practice the components of blood that are encountered are the PCV, Frozen Blood, Fresh Frozen Plasma, Platelet Concentrate, Granulocyte Precipitate and Cryoprecipitate.

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