Q about blood components

Whilst working my never ending shifts at the hospital this week, I started wondering why, when we get orders to deliver either erythrocytes (RBCs), plasma or thrombocytes they are kept in different temperatures. To clarify: RBC’s and plasma are chilled whereas thrombocytes are kept much closer to body temperature. They (blood bank personnel) always remind us to not to place the chilled and warmed bags on top of each other. But, why the different temperatures? As far as I know, they never infuse the RBCs or plasma without warming them up first, afterall hypothermia is something to be avoided to all ends, especially in trauma patients.
Is the answer something as simple as cell death? That RBCs and plasma becoming useless if they’re kept at a certain temperature too long before infusion, whilst thrombocytes don’t?

A lot of this has to do with a combination of the affect of anticoagulants used for the collection, the ability for the blood cells to tolerate temperature, and the prevention of bacterial contamination. There are two typical forms of blood component collection. Whole blood collection, when you go and donate a pint of your finest; and apheresis collection, where you are hooked up to an instrument that extracts one particular component and returns the rest to your blood (typically platelets can be donated like this).

The whole blood donations are then split up into the seperate components. I will try to go over each, please keep in mind that every donation center is different so not all these things are done the same way or using the same procedure.

(I apologize in advance if this gets annoying, but I am going to do this in a couple seperate posts, I am at work and cannot sit for long at any period…)

Your donor pint is spun in a centrifuge and now your components are seperated into a couple different bags. The anticoagulant used in these bags are usually CPDA-1 type, and CPDA-1 with adenine-saline additive; in addition to anticoagulants these are also preservatives to keep the cells alive longer in refrigeration (42 days off the top o’ my head). The refrigeration necessary to prevent bacterial growth in potentially contaminated units.

As I go on you’ll see that a lot of our storage procedures are centered along being sure that the componenet is kept as safe as possible for transfusion.

When the unit is split there are 3 other components besides red cells that we can use: plasma, platelets (thrombocytes), and cryoprecipitate. Most collection facilities strictly do packed cells and plasma though. The individual units of platelets are being replaced these days by the pheresis units; and the cryo is a pain to make as well as not used in common practice.

The plasma can either be frozen within eight hours of collection (fresh frozen plasma) or within 24 hours (FP-24), the latter containing less factor 8 but is much easier for collection centers to produce.

While the red cells are transfused for patients with a symptomatic oxygen-carrying capacity deficit (or bleeding to death), plasma is usually transfused to replace coagulation factors (or bleeding to death). Due to the fact that these factors are labile they dissapate over time, which is why the plasma is frozen for storage and will last 12 months if kept below -18 degrees C for 12 months. So in order to give a patient plasma you must crush it up and serve it to them like a cold slushee.

Okay, I keed, I keed. When plasma is ordered to be transfused it is usually thawed at 30 something degrees for 25-30 minutes. it is then given a new expiration date of 24 hours from the time of thawing. It is then refrigerated until ready for transfusion. The refrigeration, once again, is two-fold: to limit bacterial contamination and to preserve the coagulation factors for as long as possible. Many of the factors are probably still present at the end of that 24 hours, but due to the fact we just had the unit in a water bath we want to prevent any bacteria from contaminating the unit.
(Next I answer your actual question on platelets!)

Blood platelets or thrombocytes are megakaryocyte cell fragments circulating in the blood that are involved in the cellular mechanisms of primary hemostasis leading to the formation of blood clots. When activated, they release coagulation factors that promote blood clotting. Thrombocytes are the most sensitive of the three blood products, they must not be allowed to aggregate and become activated during storage, otherwise they might spontainously induce the formation of blood clots.

The thrombocytes have a shelf life of 5 – 7 days when stored on a shaking apparatus in a thrombocyte storage cabinet where the temperature is between 20 and 24 °C. The shaking should be repeated as rapidly as possible after receipt at the hospital. If the product has not been stored shaking, then it must be administered as rapidly as possible (but at the latest within 6 hours) after release. The ambient temperature until the transfusion must not fall under 18 oC (thus, do not place in the refrigerator).

Erythrocytes are specialized cells that have loose their nucleus and organelles upon maturation. In circulation, they live for about 120 days, during this time, they obtain metabolic energy by glycolytic fermentation of glucose to lactic acid. When stored outside the body, the storage medium must provide a source of glucose. They are less sensitve to storage conditions than thrombocytes, as they just need to survive and it is not their function to produce the vital but potentially dangerous molecules that trigger blood clotting that the thrombocytes do.

Erythrocytes can be stored for longer times, but their methabolic rate has to be slowed down during storage. In order to preserve quality and to prevent bacterial growth, erythrocytes must be stored at a temperature of 2 - 6 ºC and, unless otherwise indicated, have a shelf life of 35 days. Erythrocytes, which must be warmed to above 10 oC after storage, may not be again stored and must be either administered within 24 hours or otherwise destroyed. They cannot be frozen, since freezing and thawing of cells without the addition of cryoprotectants would result in the rupture of the cell membrane and destroy the cell.

In contrast, blood plasma does not contain cells and is best stored frozen below -25°C. Once thawed, it has to be used quickly in order to maintain the activity of sensitve protein components such as the coagulation factors

Platelets are stored at room temperature 20-24 degrees C, and will expire after 5 days. They are also kept on a rotator so they are never left to settle. This is because platelets are fickle, and rightfully so. Red cells are just used for transport oxygen so they’re tough, and there are no cells in plasma so there’s nothing to destroy by by freezing. Platelets on the other hand are a valuable tool in clotting. When you transfuse platelets you’re asking them to “Go forth and clot with with speed and skill, wait, NOT NOW IN THE BAG, in the patient, the patient!” So if you’re asking them to be effective, you’ve got to keep those cells happy in the meantime. This means no cold temps and keeping them aggitated while oxygenated. Since they don’t go into refrigeration that means that the cellular respiration of the cell is never slowed (like in RBCs), so in order to keep them oxygenated the aggitation helps them breathe. The secret to those platelet component bags is that oxygen molecules can pass though it. So think of the platelets like the snow in a snow globe. The more you shake it (gently) the more the platelets circulate around and stay “happy”.

The short expiration date is two-fold. I already said that keeping them at room temp keeps their metabolism high which means the cells die quicker. But also fears of bacterial contamination give them a short shelf life.

Hey, thanks guys! Excellent answers!
Now, I have another question about the same topic. Most of the time (to the tune of 95/100 approx) when we deliver either RBCs, plasma or thrombocytes they are in little bags, approx. 150 ml or so per bag (actually that pertains to the first two categories). But thrombocytes are usually in bigger bags, though the volume might be a bit less than either RBCs or Plasma (not really sure here). But lately we’ve been transporting thrombocytes in donut-shaped bags. Really odd. And I wonder what the purpose of having such a shape is. Any ideas?

As I stated earlier, a lot of different collection facilities have some different procedures.

But you said thrombocytes (platelets) in donut shaped bags? This is my WAG (btw, I’m a blood bank tech, not a doc or anything). Whenever you see a “donut” shaped bag it usually means it’s been involved in some type of centrifugation.

For instance, when we wash PRBC’s in saline they end up in a donut shaped bag, because we mix the cells with saline, then spin them which pulls the cells to the outside and drain off the saline left over. My (once again WAG) is that your donut shaped platelets might be from an older model pheresis instrument I mentioned earlier. The one that draws your blood, separates it, then gives everything except the platelets back into your blood stream.

So the possibility is that the donors blood is drawn, the collection bag is spun until they separate the platelets, then return the other blood to the donor, and leave the platelets in the “donut” shaped bag.

This is something I’ve never seen in the Northeast. Now I have some questions for you, if you’re comfortable answering them. What is your job exactly, and where do you work (region-wise, I don’t need to hospital).

Currently I’m working with transpos at the biggest university hospital over here in Stockholm. It was pretty much the only job I could get at a hospital when I first got interested in health care about 3-4 years ago. I work as a nurse at a palliative care unit as well, though that’s much less frequent. These jobs are just a means to an end. I’m studying to get my RNs licence currently, and will be finished in 2 years. After that, it’s good bye crappy jobs with equally crappy pay, and hello interesting cases! =).
You seem to have an interesting job though. Thank you for your valuable input!!

Blood products are cooled to prolong shelf life. Cooling them slows down all the metabolic and enzymatic processes, as you would expect, and it also decreases the growth of any bacterial contamination, which although small, is impossible to completely eliminate.

Platelets work fine even if they are chilled. Their job is to aggregate–to clump–among other things, helping to plug up any leaks in the vascular tree. Unfortunately, chilling platelets changes receptors on the surface (at a microscopic level) and this change in the surface causes them to get cleared by the recipient’s body (perhaps by macrophage cells in the liver) before they could get used to plug vascular leaks. Because chilled platelets get chewed up by the recipient’s body, we can’t chill 'em until we figure out how to chill them without screwing them up functionally.

Here’s a little teaser excerpt from an interesting article on the topic written in layman’s terms:

*Realizing that some factor other than shape change had to be triggering the clearance, she decided to look for the organs that handled the process. She injected chilled radioactive-labeled platelets in mice, then looked for the organs that recognized the platelets. “One of the striking results was that the chilled platelets’ clearance occurs mostly in the liver, whereas normal platelets’ clearance is divided between the spleen and the liver,” she says.

By injecting platelets tagged with different colored markers, she found hepatic macrophages that ate the platelets. But it was one receptor—complement type 3—that was important for the clearance of chilled platelets. “If the mice are missing this receptor CR3,” she says, “the chilled platelets are not eaten, so room-temperature and chilled platelets survive the same in the mice.”

“We then had a receptor that normally recognizes ‘bad stuff’ as bacteria or yeast in our body and removes it,” Dr. Hoffmeister says. “The question then was what does the receptor recognize on chilled platelets?”

An interesting finding, she adds, was that chilling platelets causes changes in their surface, leading to aggregation of the glycoprotein Ibα—a receptor for von Willebrand factor—in the lipid membrane, which is not reversible by rewarming the platelets to normal temperatures, but the chilled platelets nevertheless function perfectly. “So chilled platelets are still functional,” says Dr. Hoffmeister. “They respond even a little better to normal agonists compared to room-temperature platelets. The main problem is that they are cleared immediately from the circulation.”

“We proposed,” she adds, “that chilling primes platelets for activation at peripheral sites, where most injuries occurred throughout evolution, and if exposed to lower temperatures, they work better. But in order not to cause pathologic thrombi in our bodies, we clear these primed platelets through the liver.”

In a commentary on Dr. Hoffmeister’s research (Snyder EL, et al. N Engl J Med. 2003; 348: 2032–2033), Dr. Snyder explains that the pathways that govern the clearance of chilled platelets differ from those responsible for hemostasis, and if the mechanisms are distinct, there is a better chance for inhibiting the clearance pathways without affecting hemostasis.