Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of GenMark Diagnostics (NASDAQ:GNMK), a molecular diagnostics company, slumped as much as 10% after updating its full-year revenue guidance after the bell last night.

So what: Investors are dog-piling GenMark today following management's lowered guidance to $30 million in annual revenue versus previous expectations that had called for $35 million. Hany Massarany, CEO of GenMark Diagnostics, pointed to uncertainty regarding future revenue contributions from its largest customer, as well as ongoing reimbursement issues that are apparent through the entire pharmacogenomics sector, as the reasoning behind the tepid guidance.

Now what: Normally, a $5 million haircut isn't a big deal. However, if a company is losing money and that $5 million is a clean 14% below its original forecasts, then it's certainly going to garner a negative reaction. It also doesn't help that Natural Molecular Testing Corporation -- that aforementioned "large customer" -- recently entered in a multi-year collaboration with Luminex (NASDAQ:LMNX) earlier this month, casting a gray cloud over GenMark's future revenue stream with NMTC. Until we get better visibility from GenMark's management team and see the company moving toward profitability, this is a name I'd suggest keeping your distance from.

Craving more input? Start by adding GenMark Diagnostics to your free and personalized watchlist so you can keep up on the latest news with the company.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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