Nightly News | October 12, 2013
>>> finally tonight we all know dogs can be trained to do amazing things , but playing doctor? jill rappaport with a story of medical alert dogs and how they are saving lives.
>> reporter: k.k. and her dog j.j. are inseparable, but j.j. is more than just a pet. [ barking ]
>> good girl.
>> reporter: she's trained to be an alert and protect k.k. the 7-year-old has a rare disease called mastocytosis which causes dizziness, drop in blood pressure and other symptoms that mimic a severe allergic reaction .
>> when k.k. starts to have a reaction j.j. smells the chemical reaction and alerts us.
>> reporter: j.j. never leaves her side, even at school.
>> we have one ex-the tra person, one extra thing looking after k.k. and her senses are well beyond what we are capable of.
>> reporter: medical alert or service dogs are used to detect everything from cancer to diabetes. like with k.k.'s friend diane.
>> she lets me know by touching my leg with her nose if my blood sugar is too low or getting the too high.
>> you have animals that can sense things from so far away that we have no idea they are going on.
>> reporter: the canine sense goes far beyond a human's reach. this fur angel saved your life.
>> absolutely. i had a seizure.
>> reporter: curtis and his partner jim were home when one of their rescue dogs alerted jim that something was wrong.
>> she grabbed my pant leg, ripped my pants, pulled me out of the chair. i get back to the bedroom. she's up on the bed guarding him. he's having a seizure.
>> i never had a seizure in my life. never had warning signs.
>> reporter: curtis was diagnosed with brain cancer . he's now in remission and says isabelle is still watching out for him.
>> she's a good watch dog . untrained but meant to be in our lives.
>> reporter: true companions on alert. saving lives across the country.
>> he truly is k.k.'s guardian an gel. she knows her job.
>> reporter: jill rappaport, nbc news.