UPDATE 1-Platinum Underwriters posts lower Q1 profit

* Q1 profit falls 19 pct

* Net premiums earned falls 18 pct to $247.8 mln

* Net investment income down 30 pct to $34.2 mln

April 22 (Reuters) - Platinum Underwriters Holdings Ltd (PTP.N) posted a lower first-quarter profit, hurt by a fall in premiums at casualty, and property and marine segments, but the results topped market estimates.

The Bermuda-based property and casualty reinsurer earned $84.9 million, or $1.58 a share, for the period, compared with $105.2 million, or $1.76 a share, a year earlier.

Analysts were looking for a profit of $1.31 a share, excluding investment losses and gains, according to Reuters Estimates.

"The U.S. property catastrophe market continues to improve and we expect increased demand and higher pricing for the balance of the year," Chief Executive Michael Price said.

Net premiums written fell 22 percent at the company's casualty segment and 16 percent at its property and marine segment.

Combined ratio, which is the percentage of premiums an insurer has to pay out in claims and expenses, was 80.1 percent.