An F on a D

For those of you in familiar with the American grading system, A is the best and F is as bad as you can get unless you forget to put your name on your test earning you a 0 which is embarrassingly horrible. Fortunately I do not know this based on a personal experience, but fellow former class mates whose names I forget certainly do.
Anyway.
Recently I took a very different type if test earning me the same embarrassing feeling of an F or a 0. I find it rather humorous as it is not a test one needs to study for per say, but it was more the way my grade was delivered that earns this score a bubble.
A few days ago I took a blood test to find out the results of a bothersome a sneezing allergy. Today, my doctor handed me back my results. As it turns out I do have a minor allergy to birch and uncooked rye, random, but hey, I got the answers I was looking for!
Then we moved down the answer column and all was looking and sounding great until Dr. F paused and looked at me with the most straight face and said "and this, see this number here, this is one of the lowest numbers I have seen here in Switzerland." I started to panic and then just smiled when I realized it was probably his sense of humor. A healthy vitamin D count is between 0-300. Mine was under 50, fail.
He asked me if I drink milk, if i go out in the sun and if I like cheese. I started laughing. Umm, have we met? Do I not love he fact that the milk and cheese are the best I have ever had here and i drink it right out of the carton which I have never done?! Well, almost never, but still, the accessibility apparently isn't making it into my body fast enough. And the sun, umm are you suggesting that I spend more time relaxing on the beach or move to an exotic beach side condo to get the most D out of my cheese plate?! Thank you doctor!
Then he gave me a shot of vitamin d in the bum and a bill and sent me back to school.