D’or Yeshorim is an organization that has implemented a lab to test the blood of both boys and girls for various factors and diseases that can be detrimental to a child. The original cause was a Tai Sachs a debilitating neurological disease that effects babies in a horrendous way. They never develop real motor skills, can’t crawl, walk or even turn over on their own. Most of these babies don’t live past a few years.
When D”Y tests the results of the blood tests they can determine if the boy and girl should continue in the shidduch or if their blood DNA might bring about a horrific disease in their children and therefore stop dating. Many people carry different disease markers in their genes but for many illnesses both parents have to carry the gene such as Tai Sachs. So it is perfectly fine if either parent is a carrier but if both are carriers the D”Y will say stop the shidduch.
In addition please know that NAMES are never used when calling into D”Y for checking. Everyone who takes the test is given a card with a number on it. When you call in the person will give the NUMBERS and birth of both the boy and the girl. Someone will later call back and speak to the same person for the Yes or NO.