Blood split, spun, tested, typed
August 28, 2008
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Megan Ogilvie
HEALTH REPORTER
It has only been a few hours since the blood has left the donor's body. Soon the bag of vivid red blood will undergo a transformation, spun and split, tested and typed, turned into different products for different patients. It has entered the busiest part of its journey from vein to vein.
Today we go inside 67 College St., one of Canadian Blood Services' three main testing laboratories and seven production centres in the country.
1 Boxes of blood arrive by van, bus and plane. In most cases, the blood is delivered within hours of draining from a donor's arm. The blood is unpacked and the six vials we're tracking are whisked up to the laboratory, while their companion 450-ml bag of blood is sent to a production centre. We'll follow the vials first.
2 Once in the lab, the vials are taken to different centres. One vial will be tested for the presence of viral markers that indicate a transmissible disease. A fully automated machine, called PRISM by lab technicians, searches for markers for the following diseases: Human T-Cell lymphotrophic viruses HTLV-I and HTLV II, which can cause a rare form of leukemia in adults, hepatitis C, hepatitis B and HIV. Results are available within four hours.
3 In the meantime, a second vial of blood is being screened for unexpected red blood cell antibodies that could, in some blood recipients, set off an adverse reaction. Meanwhile, a third vial is undergoing nucleic acid testing, the method used to detect West Nile Virus, as well as the back-up test for hepatitis C and HIV. Blood is also tested for syphilis.
If a vial tests positive for any of these diseases, a technician will re-test the vial. If it tests positive again, the donor is notified. The blood associated with the vial is destroyed and the donor is deferred for life.
"Less than 1 per cent of samples are infected," says Derek Jagdeo, a senior lab technologist at Canadian Blood Services.
4 Blood type, A, O, B and AB, is also determined in the lab. Each of these groups are divided into Rh Positive and Rh Negative types. Blood type is determined by the presence or absence of antigens on the surface of blood cells and antibodies floating within the blood. The most common blood type in Canada is O Rh Positive.
More than 2,000 samples flow through the lab every day. Jagdeo says there are never, ever any shortcuts. "Our whole purpose is to make sure the unit is as safe as possible," he says. "We know we could be the patient who gets the blood."
Each unit of blood is tracked with a barcode and every process comes with an S.O.P., says Jagdeo. "That's Standard Operating Procedure," he says. "We don't do anything in this environment without one."
5 While the vials of blood have been zipping through the lab, their associated bag of blood has been busy in the component production centre.
First, the bag of blood is placed in a machine that twirls the bag of blood at such a speed that the blood separates into different components. The heaviest cells – in this case, the red blood cells – fall to the bottom of the bag. The lightest liquid, the clear plasma, floats to the top. The white blood cells and platelets, a mixture called buffy coat, hover in the middle. This process takes about 10 minutes. Special instruments extract each of the three components into separate bags.
6 The red blood cells have almost completed their journey. All that is left to do is filter out any residual white blood cells through a process called leukoreduction. The completed bags are then refrigerated. Red blood cells, which carry oxygen to tissues throughout the body and help shuttle carbon dioxide out, will primarily be used to help trauma victims, surgical patients and people with anemia.
7 Bags of plasma are tucked into a freezer. The straw-coloured plasma contains the soluble parts of blood, including glucose, antibodies and proteins, and is used in hospitals to help trauma patients.
8 To produce one dose of platelets, four units of buffy coat are pooled with one bag of plasma. All the bags must be of the same blood type. Once again, the dose of platelets are filtered for white blood cells. Each of the doses are tested for bacteria – one of many back-up systems to ensure blood is safe.
Platelets are the "sticky" components of blood that race to lesions and cuts in the body and clot to prevent bleeding.
They are critical for cancer patients, especially those with leukemia. Completed doses of platelets are stored at room temperature and rest on an agitator that rocks them back and forth.
9 The testing and production process takes about 24 hours.
Once the lab has tested the samples for disease and given the go-ahead, the blood becomes inventory.
10 Every afternoon, hospitals fax requests for blood and that night orders are packed in the appropriate boxes – plasma must have freezer packs, for example.
Susan White, the acting site manager of production at Canadian Blood Services' Toronto centre, says hospitals often make routine orders to stock their own blood bank fridges on a daily basis.
"But we also have urgent requests," she says. "A trauma arises, or somebody gets into difficulty post-surgery or a baby is born and needs transfusion support. That can happen at any time, day or night."
Urgent cases are delivered to the hospital by taxi, sometimes with a police escort.
Toronto Star