A strand of DNA recovered from Nancy Guthrie’s Arizona home is undergoing extensive testing at the FBI’s crime lab as the investigation hit the 100-day mark — and authorities continue to hold out hope for a break in the case.

The DNA sample recovered from the 84-year-old’s home in the wake of her abduction had initially been sent to a private lab in Florida by local Pima County sheriff’s detectives, despite the feds offering early on to analyze it at its state-of-the-art facility.

Several weeks after Nancy went missing, the evidence was finally turned over to federal investigators for testing.

A strand of DNA recovered from Nancy Guthrie’s Arizona home is still undergoing extensive testing at the FBI’s crime lab as the investigation hit the 100 day mark.…