Sometimes you can learn as much from a company from how it presents its results than from the results themselves.

Take Amylin Pharmaceuticals' (NASDAQ:AMLN) earnings release from Tuesday afternoon. Usually the company presents the individual sales numbers for its two diabetes drugs from the year-ago quarter for investors to compare. But not Tuesday. They were conspicuously absent. Instead, the company wants investors to focus on the 14% year-over-year increase in combined sales.

That's because its top seller, Byetta, has had a rough couple of months. Gone are the days of 25% or more year-over-year growth. Byetta has moved into a slower growth phase after grabbing all the low-hanging fruit and facing reports of pancreatitis from patients, so its growth was  less than 12% from the year-ago quarter. Thank goodness for Symlin, which grew 32% year over year, but still is a small fraction of the company's total.

Not that the growth of Byetta matters so much anymore for Amylin's long-term success. It has a second-generation version, developed with Alkermes' (NASDAQ:ALKS) extended-release technology, that can be injected once weekly instead of twice daily, like the current version. That should help Amylin and marketing partner Eli Lilly (NYSE:LLY) compete against oral medications like Merck's (NYSE:MRK) Januvia and GlaxoSmithKline's (NYSE:GSK) Avandia, as well as Novo Nordisk's (NYSE:NVO) similar once-daily drug that's under Food and Drug Administration review but appears to work better than Byetta.

I'm not sure why the company didn't reiterate the year-ago numbers, but this alone isn't a reason not to invest in the company: In fact, Amylin's stock looks more appealing at these beaten-down prices. I'd expect the investor relations department to paint the company in the best possible light, just like the marketing department should try to make the drugs sound like they're the best diabetes drug ever.

But investors shouldn't just focus on what a company presents -- be it "adjustments" to earnings or year-over-year growth. Bust out a calculator, dig a little deeper, and do your own homework.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Eli Lilly and Glaxo are Income Investor recommendations. The Fool has a disclosure policy.