Testing-lactate treshold

This evening I carried out a test once again to check out my progress conserning my speed at my lactate treshold level. I have carried out similar tests before. The first in January 2009 and the second in December 2009. They both established my lactate treshold at a heartrate around 170. The first test resulted in a lactate treshold speed of 10,4 km/h and the second in a lactate speed of 11,5 km/h.Tonight I was told that my lactate treshold had lowered to 157 in heartrate and the speed to 10,8 km/h. I was very surprised as all other results-including race results indicated otherwise. For instance I carried out Rome Marathon a few weeks ago with an average heart rate of 165. I ought to be dead if tonights results should be of any substance. Yesterday I ran a long run of 28 km, lasting 2h 42m, with an average heart rate of 158.
What I learned from the test today was that there is no sence in testing more than once a year. Additionally it is important to test at the same time every year. Further on it is vital to have somebody competent to carry out the test. Finally, the only test that counts is the race. The race that is done at the same time every year.