What Does it Mean if My Newborn Baby's Direct Coombs is Positive?

You may wonder what it means when you learn that your newborn baby has a positive direct coombs.

Well, the purpose of the direct coombs test (DAT) is to determine if there are antibodies attached to patient red cells.  In the case of newborn babies these antibodies would be antibodies from the mother.   This situation is called Hemolytic Disease of the Newborn (HDN) and it's dangerous for the baby because the antibodies break down the baby red cells, causing an increase in bilirubin. Elevated bilirubin levels in babies can cause brain damage and death if not monitored.

This can occur when the baby's blood type is incompatible with the mother's.  For example if the mother is type O, her natural Anti-A,B antibodies could attach to the baby's red cells if baby is type A. 

A more severe case is when the mother has an allo-antibody against a red cell antigen her baby has on its red cells.

 More babies used to die due to HDN but Rhogam and intrauterine transfusion help to reduce the severity of the situation.

Here is how we actually perform the direct coombs (DAT) in the blood bank.

1. We create a suspension of saline and baby red cells and wash a drop of it in a test tube.

2. Next we add Anti-IgG to the remaining red cells and centrifuge the tube.  If there is (mom) antibody attached to the baby red cells, the Anti-IgG will attach to these (mom) antibodies, causing the red cells to clump (agglutinate).  This would indicate a positive direct coombs test. 

3. We then would do a separate elution procedure to concentrate the attached (mom) antibody and identify it.

ABO Blood Types Explained

What are the Common Blood Types?

There are 8 blood types:  O Positive, O Negative, A Positive, A Negative, B Positive, B Negative, AB Positive and AB Negative.

Type A people have the A antigen on their red cells

Type B people have B antigen on their red cells

Type AB people have A and B antigen on their red cells

Type O people have neither antigen on their red cells

 

The positive and negative titles represent the presence or absence of the RH-factor. 

Blood types are genetic and each person receives one copy of their blood type gene from each parent.  A and B are always dominant over O.  A and B are codominant when both are present.  Therefore if someone inherits an A gene from one parent and a (blank) O from the other, he will be type A.   However if he inherits an A gene from one parent and a B gene from the other, he will be type AB.

 


Because blood types are hereditary, they can be used to exclude (but not include) someone as father in cases of paternity.  If two parents are blood type O, they can only produce children who are also type O.   If just one parent is AB, the child will be either A,B or AB--it would be impossible for the child to be type O.   

When we do a blood type, we type the red blood cells with Anti-A, Anti-B and Anti-D (RH).  Agglutination with these anti-sera indicates the presence of the appropriate antigen.  For example, if there is agglutination when red cells are mixed with Anti-A antisera, but none when these same red cells are combined with Anti-B and Anti-D this means that the patient is type A Negative.  We call the typing of the red cells in this way the "forward" or "front" type.

People create naturally occurring antibodies to foreign blood types around 6 months of age. 


Type A people naturally form Anti-B.
Type B people naturally form Anti-A.
Type O people naturally form Anti-A and Anti-B, actually Anti-A,B


We also do what's called a "reverse" or "back" type.  As a confirmatory measure, we take a couple drops of patient plasma and test them against known A and B cells.   If a person is type B, his plasma should agglutinate known A cells (due to his natural Anti-A), but not the B cells. 

The presence of these naturally occurring ABO antibodies is the reason why everyone can't receive blood from any random person.  A person transfused with blood of an incompatible type would have a severe hemolytic transfusion reaction could die within moments. 

Here is a compatibility chart illustrating which blood types can donate and accept from others.

As you can see Type O Negative is the universal donor and can donate to anyone and Type AB Pos is the universal acceptor and can receive blood from any type. 

Only blood bankers and some nurses/doctors would know that this chart isn't completely accurate.  Although we try to give RH-negative patients only RH-negative blood, sometimes we do not in the interest of our blood inventory.  Therefore sometimes an O-negative patient will receive several units of O-Positive red cells.  The only time we would absolutely not do this is when it is known that the patient has Anti-D (an antibody to the RH factor) and we try not to do this with RH-negative women of childbearing age because we do not want to stimulate them to develop Anti-D which could later affect any RH positive children they may carry. 

What's the Difference Between Serum and Plasma?

What is the Difference Between Plasma and Serum?

In my previous post I used the terms "serum" and "plasma" somewhat interchangeably.

Plasma is the yellowish liquid portion of the blood when the red blood cells are separated.  It includes the clotting factors like fibrinogen that cause the blood to clot.

Serum is the plasma WITHOUT the clotting factors in it.

In our blood bank we accept patient specimens in tubes with the anticoagulant, EDTA.  The EDTA keeps the clotting factors from clotting the red cells.   Therefore when these tubes are centrifuged, we are left with PLASMA on the top because the clotting factors are still present and not involved in a red cell clot.

We can also accept specimen in a plain clot tube.  These tubes don't have anti-coagulant in them and may have a clot additive to facilitate the red cell portion to clot.  When these tubes are spun, we are left with SERUM on top because the clotting factors are occupied in the clot at the bottom of the tube.

In either case, ABO and allo-antibodies are present in both the serum and plasma.

We prefer the EDTA tubes because the red cells remain liquid and we are able to pipette and manipulate them easily.   Every blue moon we get a clot tube, which is okay if we just need the serum or a couple red cells for typing, but if we need a volume of red cells for testing we cannot obtain it from the clot.

Remember:  Plasma has clotting factors.  Serum does NOT.

What is an Indirect Coombs Test?

What is an Indirect Coombs Test?


When we prepare to do a crossmatch we do a blood type and an antibody screen.  The indirect coombs test, also called the Indirect Antiglobulin test (IAT) is the antibody screen portion of pre-crossmatch testing.

The purpose of the indirect coombs is to determine if a patient has red cell antibodies in their serum (or plasma).   People can develop red cell antibodies to red cell antibodies they do not have on their own red cells.

For example, if a person does not have red cell antigen "E" on his red cells, his body would consider red cells with the "E" present on them as foreign and COULD create Anti-E antibody--although, most likely he won't. These antibodies can form after a patient has been transfused or when a woman is exposed to a foreign red cell antigen on the blood cells of the baby she's carrying.

One can also spontaneously form auto-antibodies in response to certain drugs and medications.

When red cell antibodies attach to red cells they can destroy them, lowering the patient's red cell count and hemoglobin level.

Here is an illustration of the whole concept of the indirect coombs test.

Here's how it's done:

1. We add a couple drops serum (plasma) to a drop of sample red cells with known antigens on them.  For example the red cells in tube 1 may have antigens C and K, the red cells in tube 2 may have antigens E and Fya, the red cells in tube 3 may have antigens Jka and S.

This is just a simple example: each red cell sample actually has several different antigens on them in various combinations.

2. Next we add an enhancement solution like PEG (polyethylene glycol) or LISS (low ionic strength solution)  which facilitates the attachment of any patient antibodies (if present) to its corresponding antigen on the red cells.  The tubes are incubated for about 15 minutes at 37 Celsius to simulate temperature conditions in the human body. The most significant red cell antibodies that cause transfusion reactions or cross the placenta during pregnancy are of the IgG form and react at body temperature. 

3. After incubation, the combination of patient serum (plasma), sample red cells and enhancement is washed with saline.  After washing the only thing left in the tubes are the sample red cells and any patient antibody that may be attached to them.

4.  Anti-IgG is then added to the tubes.  This is antibody TO human IgG antibodies.  I realize this may be kind of confusing but read carefully.   If there are red cell antibodies attached to the sample red cells, the Anti-IgG antibodies will bind to the Patient (IgG) Antibodies which are attached to the SAMPLE red cells.   This causes clumping or agglutination which is visible after spinning the tubes in a centrifuge.

So let's say that there is agglutination in tube #2.    Earlier I said that the red cells in sample tube #2 have antigens E and Fya on them.    This might mean that the patient has Anti-E or Anti-Fya in their serum (plasma) or an antibody to any other red cell antigen on that particular sample cell.

It's possible that two or even all three of the tubes could be positive.  This may mean that the patient has multiple antibodies or that they have an non-specific autoantibody that reacts with everything.

Further extensive testing would then be conducted to determine which antibodies are present.

Where Can I Donate Blood?

Where can I donate blood?

You can donate blood at your local blood bank like the American Red Cross or other blood collection centers.  Google blood bank donor centers in your area to find the nearest one.

Also, be on the lookout for blood drives hosted by local companies and hospitals.  Many times there will be banners and flyers on street corners announcing such events. 

Most of the blood centers bring T-shirts, gift cards and snacks as incentive for people to give blood.  Feel good about helping someone but also enjoy the small perks of being a blood donor. 

What is the Blood Bank?

What is the Blood Bank?

I work in the blood bank (lab) at a large hospital. 

Although many may not be aware of the blood bank's presence in the hospital, our department plays an important role in patient care and when a patient needs a blood transfusion its our careful expertise that ensures that the safest blood products are dispensed.

Who Works in the Blood Bank?

Let's start with the people working in the blood bank.  The blood bank (along with most of the lab personnel of other departments) consists of either Medical Technologists or Medical Laboratory Technicians. 

Medical Technologists (MT) have a 4-year bachelors degree in science and an extra year of medical technology school under their belt.  Some universities offer a 3+1 inclusive Medical Technology bachelors degree.

Medical Laboratory Technicians (MLT)have an associates degree from a 2-year program offered through community colleges. 

Both positions are accredited through the ASCP and as expected the MLTs have a lower pay scale than the MTs (but not by all that much).

In our hospital the lab is departmentalized and only MTs are allowed to do the benchwork in the blood bank.  But in smaller hospitals MLTs do work in blood bank along with the other areas.

What Does the Blood Bank Do, Exactly?

The main job of the blood bank is to crossmatch red blood cells and choose the appropriate blood components (platelets and plasma) for our patients.

Nurses and CNAs are constantly at our window picking up blood for their patients. Those who are anemic due to surgery, disease, malnutrition, etc...need blood to raise their hemoglobin level.  We also have operating room emergencies and trauma patients (car crashes, gunshots, stabbings) that require blood products to quickly replace the volume they are losing.   These emergency situations can be very chaotic and frantic, but I also find it kind of exciting.

Sometimes patients who have been pregnant or transfused in the past develop antibodies to certain red cell antigens.  This means that if they are transfused with blood containing the antigen they have an antibody against, they may have a transfusion reaction.  

We spend hours of various testing to identify what antibody or antibodies are present in such a patient. Then we spend a couple more hours to test blood units for the corresponding antigen.  We would give the patient blood that is negative for the offending antigen.   Our blood bank screens incoming type O donor blood for common antigens throughout the week so that we can have access to antigen negative blood quickly, but it's impossible to predict exactly what and how many we'll need.

All cord blood blood comes to our blood bank.  We have to determine the blood type and run a direct coombs on them.  This is important because when RH+ babies are born to RH- mothers, the mother must be given a shot of RH immunoglobulin to prevent her from developing the RH antibody that could affect any future RH+ babies she carries. 

The direct coombs is a test to see if the baby has the mother's antibodies on its red cells.  A positive result could be due to the mother's natural ABO antibodies attacking baby red cells of a different type.  OR the mother may have a red cell antibody (like the RH antibody mentioned) against an antigen on the baby's red cells--this is usually more severe than a mother-baby ABO incompatibility.   In either case, the antibodies cause the baby red cells to hemolyze, resulting in an increased bilirubin level in their little bodies.  High bilirubin in babies can cause brain damage and death.

Those are the major duties of the blood bank but there are many miscellaneous tasks that fill our work day, like unpacking donor blood from our suppliers, thawing out plasma, pulling off blood syringes for our babies, titering prenatal antibodies, washing and irradiating blood for those who require it, testing units for sickle cell, and the list goes on.

Where Does the Blood Come From?  Can I Donate Blood at the Blood Bank?

In our blood bank we do not draw blood donations.  Our hospital occasionally has blood drives sponsored by our suppliers but one would not be able to come to the hospital blood bank to donate blood.  All of our blood products come from blood donation centers like the American Red Cross and its competitors.