Shares of On Assignment Inc. jumped 13 percent in after-hours trading on Wednesday after the specialty staffing company reported second quarter profit above Wall Street expectations.

After the markets closed, the Calabasas company reported net income of $5.9 million (16 cents per share), compared with $0.9 million (3 cents) in the same period a year earlier. Revenue rose 38 percent to about $143 million, driven by high double-digit growth in its IT-engineering and life sciences staffing units.

Analysts surveyed by Capital IQ on average expected per-share profit of 13 cents on revenue of about $143 million.

For the current third quarter, the company expects earnings per share between 17 and 19 cents, with revenue between $155 million and $158 million. The Wall Street consensus is for per-share profit of 14 cents on revenue of $148 million.

On Assignment Inc. on Monday announced that it has acquired HealthCare Partners Inc., a regional physician-staffing firm based in suburban Atlanta, for more than $15 million.

“Last year, we reported that we had developed a five-year strategic plan to get to $1 billion in revenue and at least $100 million in adjusted EBITDA (earnings before interest, taxes, depreciation and amortization),” Chief Executive Peter Dameris said in a statement. “Based on the growth in our business segments and acquisitions completed to date in 2011, we believe we are comfortably ahead of where we need to be at this point in time to achieve this plan.”

Shares earlier closed up 30 cents, or 3 percent, to $10.09 on the Nasdaq, and rose 13 percent in after-market trading.