The Mystery of Blood Type Inheritance: My Mom is AB and Dad is O, but I’m O

From a biological standpoint, when you have parents with different blood types, the chances of having a child with a different blood type can be perplexing. However, once you delve deeper into the science, particularly ABO blood type inheritance, the situation becomes more manageable. Let's explore the case where a mother with blood type AB and a father with blood type O has a child with blood type O.

Understanding Blood Types and Inheritance

The ABO blood group system is one of the most well-known and studied blood types. It involves the A, B, AB, and O antigens. The inheritance of these blood types follows specific genetic rules. Here's a brief breakdown of the possible combinations:

A IAIA or IAi B IBIB or IBi AB IAIB O ii

When parents with different blood types have a child, the child's blood type can be predicted based on the parents' genotypes. However, sometimes discrepancies occur, leading to more complex scenarios.

The Common Mistake: Error in Testing or Record Keeping

The most likely explanation for a child born to parents with blood types AB and O having blood type O is an error in testing, record keeping, or both. Surprisingly, such cases are more common than one might think. Blood type AB in a newborn is often due to an error in blood sample collection, particularly from the umbilical cord (cord blood).

Poor Sample Collection and Contamination

During the collection of a newborn's blood sample from the umbilical cord (also known as Cord Blood), the sample can become contaminated with a substance called Wharton's Jelly. This results in a false blood type reading of AB Rh positive. Michael L. Jirkas highlighted this problem in an answer on Quora, suggesting that the blood group should be retested:

I would suggest you pay for your own blood type. AB in a newborn is always suspect from a bad collection of Cord Blood that can type as AB POS.

Ensuring Accuracy in Blood Type Testing

It is essential to scrutinize the blood type results, especially when they seem to deviate significantly from expected combinations. Here are some key points to consider:

Proper Sample Collection: The collection process must be performed carefully to avoid contamination. Proper guidelines are available in training programs for healthcare professionals and on reagent packaging. Sample Washing: In a lab, blood samples are often washed to ensure accurate testing. This step is crucial in preventing misleading results. Verification: results are typically cross-verified to ensure consistency and accuracy.

Conclusion

While the possibility of genetic quirks or recombination cannot be entirely ruled out, the majority of cases of ABO blood type discrepancies are likely to be the result of errors in testing or sample collection. It is always advisable to obtain a second opinion from a reputable laboratory. If you have any doubts about your blood group results, considering testing your blood again is a prudent step.

So, the next time you are puzzled by your blood type, remember that even in the realm of human inheritance, errors can occur, but proper procedures can rectify them.