4 major reasons why blood type tests can show different results

In the past few years I have been receiving several emails from people stating that their blood types have been diagnosed differently in different tests. This is not uncommon. Here are the 4 reasons why you may have gotten different results in your tests:

1) Human error

Human errors continue being the number 1 reason why different blood type tests can variate in results.

It is very sad, but human error does top this list. Doctors and nurses are often overworked and these things can happen.
One prime example is where out of 262 active duty Air Force personnel, eleven errors in blood type information were identified, including seven Rh type errors and six ABO typing errors.

If you have had two different results from two different tests, find a third place to get your blood type tested and make sure to let them know what has previously happened to ensure that they will take extra care to properly type you.
You can also order a test to do it yourself.
And if you decide to donate blood, it is less likely that donation stations will mistype you as in their case such an error could result in the death of a patient.

2) Your antigens can have weak expressions

Antigens A, B as well as the D responsible for the rh factor can express themselves weakly and therefore result in different blood type tests diagnosing you differently.

Regarding your ABO:

You can be a weak A or a weak B.
In those cases, your A or B could express itself so weakly, that some blood type tests show you as being blood type O while others will show you as the antigen you express weakly, either A or B.

Regarding the rh factor:

Weak D

In serologic testing, D positive blood is easily identified. Units which are D negative are often retested to rule out a weaker reaction. This was previously referred to as Du, which has been replaced. By definition, weak D phenotype is characterized by negative reaction with anti-D reagent at immediate spin (IS), negative reaction after 37 °C incubation, and positive reaction at anti-human globulin (AHG) phase. Weak D phenotype can occur in several ways. In some cases, this phenotype occurs because of an altered surface protein that is more common in people of European descent. An inheritable form also occurs, as a result of a weakened form of the R0 gene. Weak D may also occur as “C in trans”, whereby a C gene is present on the opposite chromosome to a D gene (as in the combination R0r’, or “Dce/dCe”). The testing is difficult, since using different anti-D reagents, especially the older polyclonal reagents, may give different results.
The practical implication of this is that people with this sub-phenotype will have a product labeled as “D positive” when donating blood. When receiving blood, they are sometimes typed as a “D negative”, though this is the subject of some debate. Most “Weak D” patients can receive “D positive” blood without complications. However, it is important to correctly identify the ones that have to be considered D+ or D−. This is important, since most blood banks have a limited supply of “D negative” blood and the correct transfusion is clinically relevant. In this respect, genotyping of blood groups has much simplified this detection of the various variants in the Rh blood group system.

Partial D

It is important to differentiate weak D (due to a quantitative difference in the D antigen) from partial D (due to a qualitative difference in the D antigen). Simply put, the weak D phenotype is due to a reduced number of D antigens on a red blood cell. In contrast, the partial D phenotype is due to an alteration in D-epitopes. Thus, in partial D, the number of D antigens is not reduced but the protein structure is altered. These individuals, if alloimmunized to D, can produce an anti-D antibody. Therefore, partial D patients who are donating blood should be labeled as D-positive but, if receiving blood, they should be labeled as D-negative and receive D-negative units.
In the past, partial D was called ‘D mosaic’ or ‘D variant.’ Different partial D phenotypes are defined by different D epitopes on the outer surface of the red blood cell membrane. More than 30 different partial D phenotypes have been described.

3) Microchimerism

Quite common in mice, chimerism exists in humans as well.

Microchimerism is defined as the presence of a small number of cells that originated from another individual and are therefore genetically distinct from the cells of the host individual.
This phenomenon is also very rare, but it can happen for example between twins where cell tissue is being exchanged. It would mean you are carrying different genes for different blood types within your cells.

4) Your blood type has changed

Strange as it may sound, there are currently 3 reported cases of a person’s blood type changing.

This is extremely rare, yet there are 3 reported cases which I am aware of where someone’s blood type has actually changed regarding both, the rh factor and the ABO type:

From blood type O positive to O negative
From blood type O negative to O positive
From blood type A to blood type O

The question is:

Have you ever had a blood type test done just to receive a different result from a previous test?
We would like to hear from you and find out what the reason turned out to be.


One Comment

  1. Shelly Mackie July 19, 2017 Reply

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