What: NxStage Medical (NXTM) is down 14% near the closing bell after releasing disappointing guidance during its fourth-quarter earnings release this morning.

So what: Fourth-quarter revenue was pretty strong, up 12% year over year. NxStage Medical booked $89.8 million in revenue, better than management's previous guidance of $86 million to $87 million. The growth is coming from NxStage's home treatment System One device, which increased 12.6%. Revenue generated from traditional in-center dialysis decreased 3.2% year over year.

On the bottom line, the company is still losing money, but at least the loss narrowed from $4.9 million in the year-ago quarter to just $2.7 million in the fourth quarter of 2015.

Management guided for 2016 revenue between $355 million and $360 million and between $87 million and $89 million for the first quarter of 2016. With revenue of $89.8 million in the most recent quarter, the first-quarter guidance is for a quarter-over-quarter decline. If NxStage hits the midpoint of the whole-year guidance, revenue will increase 6.4% year over year.

Now what: Management may be sandbagging its guidance to make sure it can exceed its forecast like it did in 2015, but investors don't seem to be taking that into account.

The fact that the company still expects a loss between $7 million to $12 million in 2016 despite the increased sales may have investors miffed. Management blamed the loss on an "investment" in NxStage Kidney Care since its products business is already profitable.

Investors will have to sit tight and wait for the investment to pay off in the form of higher revenue -- and hopefully profit -- in the years ahead.