Fresenius Medical Care shares fell after the German dialysis specialist reported another decline in U.S. treatment volumes in the second quarter.

Shares in Fresenius Medical Care were down 7.6% in European morning trading Tuesday, wiping out most of their gains since the start of the year.

The company reported a decline in second-quarter net profit to 218 million euros ($250.9 million) from 225 million euros a year before mainly due to foreign-exchange headwinds, while revenue rose 1.4% to 4.86 billion euros.

However, analysts said investors would focus on a 0.9% decline in quarterly U.S. same-market treatment volumes in Fresenius Medical Care's care-delivery segment, which generates most of the group's revenue.

The performance will continue to raise questions on the long-term growth outlook and competitive dynamics with U.S. rival DaVita in the near term, analysts at Bernstein wrote in a note to clients.

Fresenius Medical Care said its operating profit excluding special items grew 23% when adjusted for currency movements to 569 million euros. This exceeded analysts' expectations of 514 million euros, according to consensus estimates provided by Vara Research.

The company reaffirmed its full-year outlook.