A unit of blood, also known as a pint of blood, refers to the standard volume of blood that is donated or transfused. On average, one unit of blood is around 450-500 milliliters (or roughly a pint, which is 16 ounces or 473 ml). However, the exact volume of blood contained in a unit can vary slightly depending on the collection system used by the blood bank or transfusion service.
When donating or receiving blood, it is important to understand how blood volumes and units are measured in order to ensure patients are receiving the necessary amount of blood products. Tracking the number of units collected and transfused also allows blood banks and hospitals to efficiently manage their blood product inventories.
How Blood Volume is Measured
Blood volume measurement starts with the average adult, who has about 5 liters (10 pints or 20 units) of blood in their body. Here is how those units are broken down:
– 1 liter = approximately 2 pints or 4 units of blood
– 5 liters = 10 pints or 20 units of blood total in the average adult
For donation and transfusion purposes, blood is commonly separated into different components, like red blood cells, platelets, and plasma. This allows specific components to be given to patients based on their needs.
Red blood cells carry oxygen and the majority of a blood unit is composed of red cells. A standard unit contains about 200-250 ml of red blood cells.
Platelets help blood clot and a single unit of platelets is around 50-60 ml.
Plasma is the liquid part of blood and makes up about 180-220 ml of one unit.
So in summary:
– 1 unit of WHOLE BLOOD = about 450-500 ml
– 1 unit of RED BLOOD CELLS = about 200-250 ml
– 1 unit of PLATELETS = about 50-60 ml
– 1 unit of PLASMA = about 180-220 ml
The exact volumes needed for transfusion are carefully calculated based on each patient’s body size, health status, and clinical situation.
How Much Blood is Donated
In the United States, around 13.6 million units of whole blood are donated per year by approximately 6.8 million people. This blood is processed into different components like red cells, plasma, and platelets.
– Red blood cells: about 11.5 million units
– Plasma: about 13.6 million units
– Platelets: about 2.2 million units
The American Red Cross provides about 40% of the country’s blood supply, collecting over 4.5 million units of blood annually. Other organization like America’s Blood Centers and independent blood banks collect the remainder of donated blood.
Globally, around 112.5 million blood donations are collected worldwide based on data from 2016. High-income countries account for about 66% of donations but only 19% of the world’s population. Therefore, increasing donations in low and middle-income countries is an important goal to ensure adequate blood supplies are available for patients in need around the world.
Blood Donation Eligibility
Donating blood is a simple process that only takes about 10 minutes for the actual donation. To be eligible to donate blood in the U.S., donors must:
– Be at least 16 or 17 years old, depending on the state (additional parental consent required for 16-17 year old donors)
– Weigh at least 110 pounds
– Be in good health overall
Some key factors that may disqualify someone or require a waiting period before donating include:
– Recent tattoos or piercings within the past 4 months
– Travel to certain areas where malaria is endemic
– Blood transfusion within the past year
– Pregnancy or breastfeeding (must wait at least 6 weeks after birth before donating)
Other medical conditions like cancer, heart disease, bleeding disorders, or taking certain medications can also impact eligibility. Donors undergo a screening process before donating when these risks can be identified and assessed.
Blood Types
There are 8 main blood types that are categorized based on the presence of specific antigens on red blood cells. The main ones are:
ABO Blood Group System
– Type A: Has A antigens on red cells
– Type B: Has B antigens on red cells
– Type AB: Has both A and B antigens
– Type O: Has neither A nor B antigens
Rh Factor:
– Rh Positive: Has Rh antigen on red cells
– Rh Negative: Does not have Rh antigen on red cells
So someone may have A+ or O- blood for example. It is important to receive blood that is compatible with your blood type. Type O- blood can be transfused to patients with any ABO type since it lacks the A and B antigens.
| Blood Type | Compatible Types | Can Donate To | Can Receive From |
|---|---|---|---|
| A+ | A+, AB+ | A+, AB+ | A+, O+ |
| O+ | O+, A+, B+, AB+ | All Rh+ types | O+, O- |
| B+ | B+, AB+ | B+, AB+ | B+, O+ |
| AB+ | All Rh+ types | All Rh+ types | All types |
| A- | A-, O- | A-, AB- | A-, O- |
| O- | All types | All types | O- |
| B- | B-, O- | B-, AB- | B-, O- |
| AB- | AB-, A-, B-, O- | AB-, A-, B-, O- | All types |
Other Blood Group Systems
Beyond the ABO and Rh groups, there are over 30 other known human blood group systems. A few examples include:
– Duffy group: Fy(a+b-) is known as Duffy negative and is common among African populations. It conveys some resistance to malaria.
– Kidd group: JK(a+b+) and JK(a-b-) are the most common.
– MNS group: M+N+S-s+ is the most common type in this system.
– Lewis group: Le(a-b+) is common among most populations.
While these other systems are useful for research purposes, ABO and Rh factor are most important for blood transfusions.
Blood Types – Distribution Among Population
The frequency of different blood types varies globally based on ancestry and ethnicity of populations:
| Blood Type | US | Asia | Europe |
|---|---|---|---|
| O+ | 37% | 39% | 37% |
| O- | 6% | 1% | 7% |
| A+ | 36% | 27% | 44% |
| A- | 6% | 1% | 4% |
| B+ | 8% | 25% | 11% |
| B- | 2% | 1% | 2% |
| AB+ | 3% | 6% | 4% |
| AB- | 1% | 0.5% | 1% |
This distribution is related to the frequency of the alleles that code for the A, B, and O blood types. Populations where type O is more common likely had an evolutionary advantage against severe malaria infection in the past.
Rhesus negative blood types are much less common globally, especially in Asian populations. Only about 15% of Europeans and 7-10% of African Americans are Rh negative.
Uses of Donated Blood
Donated blood has a wide variety of critical uses, including:
– Transfusions: Over 21 million blood components are transfused each year in the US. This involves red blood cells, platelets, and plasma given to trauma victims, surgery patients, newborns, cancer patients, and those with blood disorders.
– Medications: Special proteins in plasma called clotting factors are processed into treatments for bleeding disorders like hemophilia. Immunoglobulins to treat immune conditions are also made from plasma.
– Research: Blood cells and samples are hugely valuable for medical research on the human genome, infectious diseases, cancer biology, and diagnostics.
– Tissue grafts: Components of blood like stem cells and platelets can help regenerate bone and soft tissues in graft procedures.
– Educational purposes: Blood is used to demonstrate laboratory techniques and train medical and biomedical students.
Without generous blood donors, none of these lifesaving and health-promoting applications would be possible. Donated blood is an absolutely vital resource in healthcare.
Cost of Blood
While blood donors are not paid for giving blood (except in rare cases), there are processing and administrative costs involved in collecting, testing, and providing blood. Overall, estimates place the cost to produce one unit of red blood cells around $200 to $300.
This includes costs for:
– Blood collection supplies: Needles, bags, tubing, etc.
– Testing: Screening blood donations for infectious diseases like HIV and hepatitis.
– Processing and storage: Handling, separating, and preserving blood components.
– Hospital expenses: Like specialized blood refrigerators and transfusion administration costs.
– Staffing: Phlebotomists, nurses, technicians, and other personnel.
Despite these behind-the-scenes costs, blood itself is not sold for a profit. Patients are billed based on the cost of processing and transfusing the blood received. A unit of red blood cells is around $200-300, platelets about $500-800, and plasma around $30-50.
Insurance policies normally cover most blood transfusion expenses, but uninsured patients can face heavy medical bills without this coverage. This highlights the importance of widespread healthcare reform to decrease costs and financial barriers to receiving life-saving blood.
Blood Shortages
Although around 38% of the US population is eligible to donate blood, less than 10% of those eligible actually donate annually. This can lead to frequent blood shortages, when blood supplies drop to dangerously low levels.
Both predictable factors and unexpected events can cause shortages, including:
– Lower donations during summer months and holidays when people are busy or traveling. Also lower turnout at high school and college blood drives.
– Increased demand after natural disasters, mass shootings, or other crises increasing the need for transfusions.
– Weather closures making it difficult for donors to reach blood drives safely.
– Infectious outbreaks like COVID limiting eligible donors and blood drive sites.
Shortages are often for specific blood types like O negative and O positive. Type O blood is universally compatible with all patients.
Blood banks attempt to mitigate shortages by importing blood products between regions and engaging in campaigns to increase donations. But shortages can still impact the availability of blood for essential procedures.
Blood Management Strategies
Since blood is a scarce resource, the WHO recommends these blood management strategies:
– Appropriate clinical use of blood – give patients evidence-based transfusion guidelines. Avoid over- or under-transfusion.
– Patient blood management – use techniques to reduce blood loss during surgery like hemodilution and cell salvage.
– Optimize blood supply management – use information systems to track inventories and distribute to areas of need.
– Improve accessibility of transfusion – provide adequate refrigeration, transportation, and trained staff.
– Screen all donated blood -mandatory infectious disease testing to ensure safety.
– Increase voluntary donations – engage communities and replace family/paid donation.
Following these best practices allows available blood units to be used judiciously and equitably.
Conclusion
A single unit of donated blood can save up to 3 lives through components like red blood cells, plasma, and platelets. But only a small fraction of eligible individuals donate regularly to meet this need. While each unit costs around $200-300 to collect and process, donated blood itself is a free but precious gift to patients in need. Improving awareness about donating, along with optimizing clinical use and supply management, are key to ensure blood shortages do not cost additional lives that could be saved.