O - blood-type nail biter

I have been so pleased to be able to test newborn's blood type at home in the case of an RH- mother in past years instead of having to get a prescription ahead of time and head out to the hospital upon the baby's arrival like we did 10 years ago.

The last baby we tested caused me to retest, and retest again! I wonder if anyone else has had this experience. In the test we use, available at In His Hands, 4 small circles each containing a different reagent are wet and then put in contact with a drop of cord blood. By comparing which reagents the blood reacts with ( turns to a grainy pattern) or not (remains smoothly liquid) to the blood-type chart contained in the test you can determine the baby's blood type. The fourth circle on the test is the control.

Interestingly if the control reacts then the test is invalid. Conversely, for the test to be working correctly the control does nothing. Here in was the nail biting issue. The control worked fine. It did nothing, but so did the other three circles! I checked the expiration date ( it was in 2009), and reread the directions even though I just had a reread them and had used the test before. Having refrigerated the test tube containing the cord blood immediately I allowed it to warm to about room temperature and tested again thinking that may have been a problem. Nothing happened, as I looked over at the parents and tried to look reassuring though they were not paying much attention really.

After a third test, thankfully we bought a package of them and had extra on hand, I reviewed the blood-type chart even though I thought I had no results. It seems that an O- blood type turns up no reaction. It reacts with no reagents and of course the control is made to do nothing. The Mom did not have O- blood as I had immediately hoped, as that would have provided some confirmation to the three identical test results that "looked" like mistakes, but I checked the parents blood types when I got home to ensure that the O - was possible given the types of the parents. I explained the issue to the Dad who was very comfortable with the results.

Has anyone else turned up these results? I wish the control reacted in some way. As the test stands O- blood types make for a nail biter.