My daughter, Margaret, is an unsung hero. I must speak for her. When she was diagnosed with phenylketonuria (PKU) at 13 months, it was already too late. Her brain had been devastated by this insidious metabolic disease.

Because of this, her uncle — Dr. Robert Guthrie of the children’s hospital in Buffalo, N.Y. — speeded his research to diagnose PKU earlier. His simple “heel prick” became the newborn screening test currently being used worldwide. It became Minnesota state law in 1965. Margaret was born in 1958.

With modern technology, Guthrie’s test now “picks up” 54 additional debilitating and sometimes fatal disorders. Treatment can then start far earlier. Cystic fibrosis is one such disease.

Blood spots must be saved for the emergencies when children suddenly become ill and for helping to develop new tests. Legislators, listen to the pleas of eminent pediatricians in Minnesota (“The case for keeping newborn test results,” March 1). They have seen our heartbreak as parents. They love children.

It was too late for my beloved daughter. Don’t make it too late for our other beautiful Minnesota babies.

Mary Lou Doll, Minneapolis