S.R.
Well my pediatrician was concerned about my 2nd daughters growth when she was between 2 and 3. She "fell off the chart" and was never very high on it to begin with. We did some labs, and he also referred us to a nutritionist type person (or was it a dietician?) and she gave us a lot of tips about beefing up her diet. I think that helped a lot. We did some special labs also, but that was just a blood draw. He almost ordered the bone x-ray thing, but decided not to because the labs were decent. Eventually she got back on the chart. I asked him, is it possible she is just having a reverse growth spurt, like a latency period? And he said yes, totally, but his job as a pediatrician was to watch for signs of potential issues and look into them, so that's what we were doing.
Personally I was never too worried about it, mostly because my older daughter was also small (and a far poorer eater, but whatever) and she seemed otherwise healthy. I also told my pediatrician that I have a cousin with Turner's Syndrome (a growth-related syndrome for which she had to take hormones growing up, and for some reason makes her unable to carry children). He said that was irrelevant because it's not a genetic syndrome but a chromosomal one.
Anyway, that was my experience. At the last appt, he was pleased that she was "back on the chart" and he did order one more round of labs, which I never did... oops. I was kinda over all the scrutiny at that point. Her annual is due this month though so we'll see what he says.