|Don't ask to ask, just ask|
I tend to agree with lemming. Perhaps you should verify that the field in question was, in fact, included in the specifications you provided to the coder. (Based on your initial reaction, I presume that it was.)
(I'm also presuming that there's more to the story, given the title you gave the thread.)
Next, I would time myself out long enough to be able to approach the coder with something along the lines of, "um, I can't seem to find this data we're supposed to be tracking. Am I missing something?" This provides a graceful exit in case an honest mistake was made, either by your coder or you.
Finally, once you figure out what the problem is and what needs to be done to resolve it, then I would tell the coder that, "OK, this needs to be resolved quickly and I'm going to send an email to follow-up." That will give you a paper trail, in case it becomes necessary, and highlight to the person involved that it's serious enough to be tracked.
At that point, you see what happens. If the problem is resolved, then simply make a note to discuss unit testing and requirement checklists during your post-mortem. In fact, you might even try to generate some discussion about how to improve that. Use care not to mention specific problems or to embarass your staff in front of your customers, their peers, or others. (That doesn't help in the slightest and, in fact, hurts a great deal.)
In other words, once the specific problem is resolved, you'll want to focus on preventing similar incidents in the future. While there are times big sticks are useful, I've rarely seen them effectively applied to improving employee morale or programmer accountability. YMMV.