What is a unit of blood?

Blood is collected in plastic bags which contain a fluid which prevents blood from getting coagulated. Blood banks usually draw 450ml of blood when the blood donation is in the blood bank and 350ml when the blood donation is in a blood donation camp (outside the hospital). This blood, along with the anti coagulant present in the bottle or bag, is known as one unit of blood.

In which situations is blood transfusion required?

There are many situations in which patients need blood to stay alive:

  • A patient needs blood after a major accident in which there is loss of blood.
  • No major surgery is performed without blood as there is bound to be blood loss. (On an average, for every open heart surgery about 6 units of blood is required.)
  • In miscarriage or childbirth, the patient may need a lot of blood to be transfused to saving her life and also the child’s.
  • For patients with blood diseases like severe Anaemia (especially Aplastic Anaemias), Leucaemias (blood cancer), Hemophilia (bleeding disorder), Thalassemia etc. repeated blood transfusions are the only solution.
  • In many other situations like poisoning, drug reactions, shock, burns, blood transfusion is the only way to save precious human life.

Is the collected blood tested before transfusion?

Yes. ALL the blood collected in the blood bank is tested for the following diseases:

  • Hepatitis B & C
  • Malarial parasite
  • HIV I & II (AIDS)
  • Venereal disease (Syphilis)
  • Blood Group Before issuing blood, compatibility tests (cross matching) is also done. The results of these tests are kept highly confidential and not shared with anyone. Only in case of major ailments found in the donated blood, is the donor informed about it.

Can we separate blood into its components?

Yes! Now with technical advancements, we can make components of blood and store them. For example, plasma can be separated from whole blood and stored up to one year in frozen state at -80 deg C temperature or below. This is called Fresh Frozen Plasma. Similarly there are other components like Platelet Rich Plasma; Platelet Concentrate (can be stored as a life saving measure up to 5 days now at 22-24 degrees C in a platelet incubator and agitator); Cryoprecipitate (which is very useful in treating bleeding disorders due to the deficiency of factor VIII and IX); Factor VIII and IX; Albumin, Globulin and many others.
Now days, many blood banks convert the blood in its components and store it. This is because many patients do not require whole blood. For example, a patient whose haemoglobin is low (anaemic), may just require Packed Cells i.e. only red cells; a patient with burns may need more of plasma than cells; a patient with hemophilia may require only Factor VIII.
With the advent of cell-separators, we can also directly draw just a particular component from the donor.

How long can blood be stored?

If the blood has not been segregated in its components, it can be stored for up to 35 days, when kept in CPDA anti coagulant solution and refrigerated at 2-4 deg C. For segregated components, the storage time varies as mentioned below:

  1. Platelet Concentrate - 5 days
  2. Platelet Apherises – 5 days
  3. Platelet Rich Plasma - 5 days
  4. Packed Cells – 35 days
  5. Fresh Frozen Plasma - 1 year
  6. Cryo Anti Hemophilic Factor – 1 year
  7. Cryo Poor Plasma – 5 years

Can blood of animals be transfused to human beings?

There has been a lot of research in this field, but it has not led to any success till now. Only the blood of a human being can be transfused to another human being.

Can a person with 'A' group donate blood to a person with 'B' group?

No, it cannot be done. This is due to the reason that the blood of A Group people contains anti-B antibodies. In B group people there are anti-A antibodies. If we give A group blood to a B group patient, it can lead to serious consequences.
AB+ is the universal recipient because AB Group contains both anti-A, anti-B antibodies.
O- is the universal donor because O Group contains neither anti-A and anti-B antibodies.

Why are Rh-negative and Rh-positive incompatible?

'Rh-negative' and 'Rh-positive' refer to whether your blood has Rh factor. Rh factor is a protein on red blood cells. If you have Rh factor, you're Rh-positive. If you don't have it, you're Rh-negative. If you are Rh-negative and you are injected Rh-positive blood, your body will create antibodies for the Rh-positive factor. This can lead to destruction of red blood cells in your body faster than the speed with which they are replaced.

Do blood banks use 'O-' as a universal donor to transfuse blood to people with other blood groups?

For all practical and routine purposes, it is ideal and preferable to transfuse to the patient the same group of blood which he belongs to. It is only under very dire emergencies that the blood banks take O group as universal donor and AB groups as universal recipient. Also, under no circumstances O group can get any other blood except O. Similarly A group patient cannot be given B group blood and vice versa.

What happens to patients who are given incompatible blood (mismatched blood)?

The following symptoms may occur after only a few ‘ml’ of blood have been given:

  • Patient complains of shivering, restlessness, nausea and vomiting. There is precardial and lumbar pain.
  • Cold, clammy skin with cyanosis.
  • Pulse rate increases, respiratory rate increases. Temperature increases to 38 to 40 deg C. [101 to 105 F].
  • Blood pressure falls and patient passes into a state of shock.
  • Haemoglobinaemia, haemoglobinurea (urine turns red); oliguria (urine becomes scanty or the urinary output is reduced) and anuria (total output of urine becomes 200 ml. a day)
  • Jaundice appears after a few hours and in some cases anuria persists and uremia develops. This may lead to death.


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Who can donate blood?

There are various criteria associated with donating blood. The major ones being:

  • Eligible age: 18-60 years old
  • Weight: The weight criteria varies with hospitals, however the govt. guidelines require the min. weight to be 45 kgs
  • Haemoglobin: The minimum haemoglobin content required is 12.5 gm%
  • Not donated blood in the last 3 months
  • Not consumed alcohol, taken any antibiotics within last 2 days
  • Taken a meal within the last 2 hours
Besides these, there are various other criteria. Click on the tab "Blood Donation Criteria" above to know more about those criteria.

What are the different kind of blood donors?

There are three kinds of blood donors: -

  • Professional Donors: They donate blood for benefits (money, gifts, etc.). Such donations are very risky, as there are chances that the donor might not reveal the disease/ailment he is suffering from. It is illegal to take blood from any professional donor.
  • Replacement Donors: In case of requirement of blood for someone known, family and friends come together to help meet the requirement. Such donations, received from a relative or friend of the patient are replacement donations. The blood bank issues blood to the patient in lieu of these replacement donations.
  • Voluntary Donors: Voluntary donation is considered to be the highest act of selfless service. In this, a donor donates blood without knowing the identity of the patient for whom he/she is donating. Motivated individuals who donate blood in blood donation camps or by going to blood banks without knowing about any requirement, fall in this category.

Is it safe to donate blood? What is the process of blood donation?

Yes, donating blood is very safe. Blood banks use totally sterile disposable blood bags and needles while taking your blood. You can also confirm this with the doctor who is taking your blood, he/she will happily clarify all your doubts about the safety.
Find below, the process followed for blood donation in general:

  1. Complete the donor registration form that includes your name, address and a few other details.
  2. Go to the doctor, who will do a simple medical checkup. You will be asked a few questions about your health. The doctor will also take your Haemoglobin test by either physical examination or by a prick on your finger tip.
  3. Proceed to a donor bed where your arm will be cleaned with antiseptic. The donation process will start after that
  4. During the blood donation process, you will be donating either 350ml or 450ml depending on factors like venue where you are donating, your weight, etc..
  5. Rest for about 15 minutes after the process is over. Apply a band-aid at the place of the prick.
  6. Eat the refreshments provided by the blood bank. Do not forget to take your donor card when you leave the venue.
How long does the process take?

The procedure is done by skilled, specially team from a blood bank. While the blood donation process just takes about 10-15 minutes, the full process from start to finish (filling form, post donation rest, etc) takes about 30 to 40 minutes.

Does the needle hurt?

There may be a little sting when the needle is inserted, but after that there should be no pain during the donation.

Does the donor suffer from any harmful effects post blood donation?

Generally, No. There are no harmful effects of blood donation, however in 1% cases you might face the following issues:

  • Weakness/ Fainting/ Nausea: A person may feel week after donating blood. This generally happens if a person did not have proper food, sleep before donating blood. It is important to have proper rest and refreshments after blood donation in order to avoid this. Anyhow, if you do feel weak, lay down and raise your feet above, keep moving them so as to maintain the circulation of blood.
  • Red Marks/ Swelling/ Blue patch on the arm: While removing the needle, there are chances of blood getting under the skin, which then reacts and leads to the red marks/blue patch. Such a patch can also pain sometimes. Apply cold pack for first 24 hours and thereafter a warm pack. The pain goes in 1-2 days, however the patch can take around 2-3 weeks to settle/disappear, however. If you feel excessive pain, take a pain killer (acetaminophen). Besides all this, we do recommend, that you consult a doctor/talk to the blood bank people. They will offer the best possible solution.
  • Bleeding: Sometimes the wound opens up again and starts bleeding (can even happen an hour after the donation). This happens if the donation site on the arm experiences strain and the newly repaired skin breaks (could be due physical stress/ hurry in removing the bandaid etc.). If it happens, clean the open wound, put cotton/ band-aid, fold the arm and wait for it to repair again- adopt the same procedure that is followed after donation.
Can the donor work after donating blood?

Yes! Take it easy for the first 30minutes- 1 hour after donation. After that, routine work is absolutely fine. Rigorous physical work should be avoided for a few hours.

How long will it take for the body to replenish the blood?

The body replaces blood volume or plasma within 24 hours. Red cells need about 21 days for complete replacement.

How frequently can someone donate blood?

The Indian govt. rules state that a person can only donate blood once in three months. Always have a minimum 3 months gap for your own safety. This condition is only for blood donation, platelet donation conditions are different. For details on platelet donation, click here


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The various criteria associated with donating blood are:

Basic Criteria

  • Eligible age: 18-60 years old
  • Weight: The weight criteria varies with hospitals, however the govt. guidelines require the min. weight to be 45 kgs
  • Haemoglobin: The minimum haemoglobin content required is 12.5 gm%
  • Not donated blood in the last 3 months
  • Not consumed alcohol, taken any antibiotics within last 2 days
  • Taken a meal within the last 2 hours

Criteria for Female
Females cannot donate blood:

  • While lactating
  • During menstrual period (6 to 7 days)
  • Post delivery (within 1 year)

Temporary deferrals
One cannot donate blood if the person has faced any of the below mentioned problems within the time period mentioned alongside each issue:

  • Major Surgery (1 year)
  • Typhoid (1 year)
  • Dog bite/Rabies Vaccination (1 year)
  • Unexplained weight loss/ continuous low grade fever (1 year)
  • Dental extraction or root canal treatment (6 months)
  • Dengue or Yellow jaundice (6 months)
  • Tattooing or body piercing (6 months)
  • Intravenous drug abuse (6 months)
  • Malaria (3 months)
  • Vaccination (2 weeks)

Permanent deferrals
One cannot donate blood ever, if he/she has faced/is facing the following problems:

  • Abnormal bleeding disorder
  • Heart/ Kidney/ Liver/ Thyroid Disorder
  • Epilepsy or mental disorders
  • Tuberculosis or Leprosy
  • Asthma
  • Cancer
  • Insulin dependent diabetics, Uncontrolled High BP.


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