What happens to your blood after you donate it? Demystifying blood donation.

Seven small glass refrigerators in the back room of a large office building just off Interstate 10 and Loop 410 hold the entire donated blood supply for San Antonio and South Texas.

The milk sections at most local H-E-Bs are larger and more stocked.

Sorted by blood type and waiting to be shipped out to one of the dozens of hospitals in the South Texas Blood and Tissue Center’s service area, this is the entire blood supply for not just San Antonio, but also the Rio Grande Valley and much of the Hill Country.

“This is what we have for all our communities, right? This is it for over 100 hospitals and 48 counties,” said Roger Ruiz, the organization’s senior communications specialist. “This is what they rely on.”

Staff members responsible for collecting, sorting, testing, mixing, packaging and shipping the blood-filled bags — which they refer to as “units” — continue with their work, accustomed to seeing the meager supply in these fridges.

With the clock ticking on how long each donation lasts from extraction to transfusion, lives depend on them working quickly and diligently.

Celebrating its 50th year in San Antonio this month, South Texas Blood and Tissue was born out of events that followed blood shortages of the 1970s, spurred on by hepatitis outbreaks and the introduction of the National Blood Bank Act of 1972.

Today, it sits under the parent company BioBridge Global, a San Antonio-based family of nonprofits that also includes QualTex Laboratories, GenCure and The Blood and Tissue Center Foundation.

While many San Antonio residents have donated blood to the center at some point in their lives — whether at their high school’s annual blood drive or a quarterly blood drive at one of the city’s largest employers, like USAA — it may surprise San Antonians how much work goes on behind the scenes after the needle comes out of their arm.

Here’s an inside look at what happens after you get up from the chair sporting a cotton ball armband.

‘Whole blood,’ platelets or red cells

Blood drives take place all over San Antonio — often at high schools, colleges and businesses — but the South Texas Blood and Tissue Center also has nine donation sites collecting blood year-round.

How much blood comes in each day varies largely, depending on the time of year and need, with summer tending to have fewer donations as students are out of school, Ruiz said.

When giving blood to the South Texas Blood and Tissue Center, a donor can donate “whole blood,” platelets or double red cells. While the first two are more common, all three types have far-reaching impacts, Ruiz said.

“Whole blood” is blood in which the red blood cells, platelets and plasma are left mixed together and intact, Ruiz explained. This is blood drawn straight from the vein and put into a bag. This blood can be separated into components that can each be used to help save a life, depending on what the receiving patient needs, he said. Whole blood donation takes about an hour.

Donors can also give platelets, the tiny components in blood that help with clotting. Platelets are most often used by cancer patients and others facing life-threatening illnesses and injuries. Platelet donation typically takes about three hours.

During platelet donation, the blood is drawn from the donor and centrifuged — put into a machine and spun extremely quickly — with the donor’s red blood cells and plasma going back into their other arm, while the platelets are separated into their own bag. Plasma is the component of blood that carries water, salts and enzymes.

A double red cell donation is similar to a whole blood donation, except a different machine is used to allow the donor to safely donate two units of red blood cells during one donation while returning their plasma and platelets to them. Red blood cells are typically given to people with sickle cell anemia or who suffer significant blood loss due to trauma or surgery.

Donors who participate in a double red cell donation are not allowed to donate again for 16 weeks in order to naturally let their own cell levels recover, while those who donate whole blood can donate every eight weeks and those who donate platelets can do so once a week.

Filling orders

After the blood is collected, it is put into a cooler or ice chest for transportation to the South Texas Blood and Tissue Center’s components and manufacturing lab where manufacturing associates — a type of lab tech — will sort it into components.

The blood or pre-sorted components need to be labeled and organized within eight to 10 hours after a donation occurs, said Julian Salcido, the component manufacturing manager for the South Texas Blood and Tissue Center.

The manufacturing associate takes each bag of whole blood, gives it a unique barcode, scans it into the center’s computer system and puts it into a special cup to be centrifuged to be broken down into its components.

Hospitals place daily orders for blood and its components that Salcido and his staff work to fulfill, using a daily production plan.

It’s then the manufacturing associate’s job to make sure the blood bags are separated into the proper components to fill each of these orders, he explained. Some bags will remain as whole blood, while others will undergo a rigorous separation process.

Once all the bags of blood have been placed into the special cups, the centrifuge is loaded up, and the bags are spun at incredible speeds — roughly 1,000 rotations per minute or more — for about four to six minutes, explained manufacturing associate Rudy Rodriguez.

This separates the blood into plasma, platelets and red blood cells, with the latter being the most dense and sinking to the bottom of the bag.

The white layer between the red blood cells and plasma is known as a buffy coat. This coat can also be separated to be used for research, Salcido noted.

These spun bags are handled extremely gently as they are loaded into an automatic blood component separator, or “expressor,” to go through the process called apheresis, or the separation of plasma and platelets from the red blood cells, which only takes about three to four minutes.

The plasma and platelets are sealed off into separate bags. The plasma is flash-frozen and can be stored and used for up to a year, Salcido said.

The platelets, on the other hand, are immediately taken to a separate lab across the hall where they will be tested for bacterial growth over the course of 48 hours. Once cleared, the platelets are ready to be used for transfusions, said Taika Gutierrez, a lead tech in the platelet lab. Platelets are only viable for about seven days, compared to red blood cells’ 42 days, Salcido noted.

The bag with the remaining red blood cells is loaded onto a medical pole or “tree” where the red cells are mixed with a solution and then hung upside down so that the red blood cells will have to pass through a small cotton-like filter that separates them from the white blood cells.

Because white blood cells are bigger than red blood cells, they are trapped by the filter, and then disposed of. This process is called leukocyte reduction.

White blood cells, which protect against outside pathogens that can cause illness and disease, are more likely to trigger a reaction in a patient receiving a transfusion, so they’re removed to increase the likelihood of a successful procedure.

Once the blood components have been separated and labeled, they can be sent to the center’s packaging room. Here, they’re put into cardboard boxes lined with styrofoam and insulated with dry ice packets for safe transport.

For emergencies, such as after the 2022 Uvalde school shooting, the center has a helipad on site and can quickly disperse units as needed, Ruiz said. Fire, EMS and other emergency responders also come through in the afternoon to pick up units, he added.

Testing for infectious diseases

Meanwhile, the three separate vials of blood and/or platelets collected during the donation process are sent off to another part of the building that houses the local branch of QualTex Laboratories.

It’s here these samples are tested for any bloodborne infectious diseases, atypical or unusual antibodies and to identify the donor’s blood type.

Since time is of the essence, a donation needs to be processed at the same time a portion of the blood or its components are tested.

The tubes are placed into an automated lab track system — a gigantic conveyor belt system where they will run through for several tests. The system runs the length of the room, dipping into corners and hallways to fit the stops along its long, winding body. The track has cameras and scanners throughout that keep the blood moving efficiently.

“We’ve got about 15 to 17 different tests that are required by the FDA that we run,” said Scott Jones, senior vice president and chief scientific officer of BioBridge Global, while giving a recent public tour of the facility. These 15 to 17 tests check for any of the hepatitises, HIV and syphilis among other diseases, he noted.

If a sample comes back positive for one of these, both the donor and the local public health authority are notified, Jones added. All samples, whether positive or negative for diseases, are disposed of through the biohazard disposal process.

Another of the tubes is placed into smaller automated testing units that check the blood for Zika and West Nile Virus, explained Sofia Wong, a QualTex lab tech.

Samples that test clean mean that donor’s blood can be sent to distribution, Jones said.

Patient needs

For some patients, it’s not as easy as receiving a transfusion of whole blood or of blood’s separated components. Sometimes, they need an even more specialized blood product or the patient will have a negative reaction.

For these recipients, specialized products have to be created by “blood alchemists,” or hematologists or specialized techs in a separate lab.

Often patients with certain types of cancers or sickle cell anemia have developed antibodies against specific types of transfusions, Ruiz said.

The South Texas Blood and Tissue Center also collects umbilical cord blood donations and maintains the cord blood bank for all of Texas. Blood taken from an umbilical cord at or shortly after a mother gives birth contains stem cells, which can be used to treat diseases like some forms of cancer and anemia.

The cord blood is kept in large nitrogen-cooled freezers that can reach temperatures as low as minus 112 degrees Fahrenheit. Some of the bank’s cord blood samples are almost 20 years old, but are still viable and used worldwide, Jones said.

“We have a little over 14,000 units that are stored here,” Jones said. “Basically they’re in the registry. Last year, we actually shipped out more than 300 cord blood units for patients.”

A not-so-far-away future

BioBridge Global’s nonprofits don’t just collect and test blood and tissue for the South Texas area, they also also perform global research, Jones said.

GenCure, a full-service biomanufacturing organization that focuses on regenerative medicine, for example, works on “scaling up” stem cells — helping them grow to more usable and testable sizes so they can be experimented with.

One of the more recent donations South Texas Blood and Tissue Center has started taking is placentas — organs that form in the womb during pregnancy to provide the developing fetus nutrients and oxygen — which can be sliced up and used to heal patients with serious burns, sores and other wounds that are difficult to heal.

The company is also looking at ways to manufacture artificial blood — non-human blood that can be accepted by the human body, Jones said.

“Our mission is to save and enhance lives through the healing power of human cells and tissues,” Jones said.