Successful investors think about the future by focusing on what the new opportunities might be. They also pay attention to threats that could emerge that might impact the stocks they own. Sometimes, those threats come out of the blue, but other times, they're identifiable well in advance.

If you own shares of Abbott (NYSE: ABT) or (NASDAQ: DXCM), there's a looming threat to know about. It's not from another medical device make -- it's from an innovative biotech company. Should Abbott and DexCom investors be worried about Vertex Pharmaceuticals (NASDAQ: VRTX)?

DexCom's entire business is built around diabetes. Every penny of the company's first-quarter revenue of $921 million came from its continuous glucose monitoring (CGM) systems. These CGM devices are primarily used to monitor insulin levels for individuals with type 1 diabetes (T1D), although they can also be used by people with type 2 diabetes.

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Source Fool.com