There are many different reasons that you may have gotten this letter from your doctors
">doctor's office. I assume that you recently had some blood work done, and the letter is probably in reference to those results.
Every doctor and every doctor's office is a little different in how they handle results from blood tests. Many will just send a letter or make a brief phone call if everything is completely normal stating something to that effect. However, if there are any abnormal test results at all, many offices will want to talk directly with you so that they can explain what the results mean.
Therefore, based on the letter, it is possible that there is an abnormal test result that your doctor wants to talk to you about face to face. This doesn't mean necessarily that something very serious is wrong (and in fact if that was the case then they would probably have called you directly rather than just sent a letter).
In conclusion, it is important to make the followup appointment with your doctor's office, at which time they should be able to talk to you about the results of the lab tests and what they mean.