Some basic research would have told you that you can very accurately judge lactate threshold with a well executed run or two. You absolutely don't need to take blood to get an accurate estimation. Will running test in a lab and taking a blood test be more accurate? Of course it will. But rarely needed by an average runner. Yes the only way to measure the actual lactate lvl in blood, is a blood test. But the ? was determining lactate threshold, which with a little basic research would have helped you understand that it is possible. An to answer the ? being asked, unfortunately I don't think the 245 does. Most models since do have the actual feature built in so you don't have to do the math yourself, however its really quite simple once you've determined your max heart rate.
But you can do a field test, 20-30 minute for Running Lactate Threshold Heart Rate and you'll be able to.manually input the results as use the HR zones with LT.
Trainingpeaks or TrainRight blog will have the specifics for the testing.
