Exactly what is a titer test? I've never heard of this and my vet has never mentioned it. When I first moved to OK and took my Shelby in for her yearly checkup and shots, the vet did a heart worm test (neg.) and gave me her Heart Guard pills for a year. The following year when I took her in, I was told I didn't have to have her tested every year as long as I kept her on her pills...which I have always done religiously. However, when I moved to AL I was told I still had to have the test done every year. Is this something that varies from state to state?? It seems to me that's what the Heart Guard pills are for...to prevent heart worms. Shelby is almost 13 and after reading these posts, I think I am going to just go with a 3 year rabies vaccination and her Heart Worm treatment from now on. She's an inside dog for the most part and I don't worry too much about any other problems.