Abbott's Libre launch is off to a strong start in the U.S. with more than 25,000 patients having started on the device since the launch in early December, JPMorgan analyst Michael Weinstein tells investors in a research note. It remains way too early, however, to say what percent of patients will stick with the device, the analyst adds. The Libre launch reinforces the analyst's cautious stance on shares of Dexcom (DXCM). He expects Dexcom's growth to slow over the course of the year and for 2019 to prove "much more challenging" than 2018. Weinstein has an Overweight rating on Abbott and Neutral rating on Dexcom.

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Pre-earnings options volume in DexCom is 11.4x normal with calls leading puts 11:2. Implied volatility suggests the market is anticipating a move near 5.8%, or $8.05, after results are released. Median move over the past eight quarters is 5.4%.