April 24 (Reuters) - Scientific instruments maker PerkinElmer Inc on Thursday reported a higher-than-expected first-quarter profit, helped by increased demand for its medical diagnostics products and continued double-digit growth in China.

The company, which also sells environmental testing products, posted a net profit of $34.2 million, or 30 cents per share, compared with a profit of $32.2 million, or 28 cents per share, a year ago.

Excluding one-time items, PerkinElmer said it had adjusted earnings of 46 cents per share. Analysts on average had expected 44 cents per share, according to Thomson Reuters I/B/E/S.

The company tweaked its full-year earnings forecast and now expects adjusted 2014 earnings of $2.42 to $2.46 per share, up from its prior view of $2.40 to $2.45. Analysts on average are looking for $2.45 per share.

Revenue for the quarter rose 5 percent to $531.9 million, edging past Wall Street estimates of $531.3 million.

(Reporting by Bill Berkrot, editing by G Crosse)