Genetic testing instrument maker Affymetrix Inc. said Wednesday its profit rose 42 percent in the fourth quarter as its costs decreased, offsetting lower revenue.

Affymetrix said its net income grew to $4 million, or 6 cents per share. In the fourth quarter of 2009 it reported a profit of $2.8 million, or 4 cents per share. Revenue fell 4 percent, to $84.9 million from $88.8 million.

Analysts expected a profit 2 cents per share and $85.1 million in revenue, according to FactSet.

The company said consumable product revenue declined 12 percent to $63.4 million, and instruments sales slipped to $8.5 million from $9.1 million. Service revenue edged up to $6.4 million from $5.9 million, and royalties and other revenue grew to $6.6 million from $1.9 million.

However, Affymetrix said its selling, general and administrative expenses shrank 17 percent to $28.7 million. Its total quarterly costs fell to $79.7 million from $86.3 million. The company also benefited from lower interest expense in the period.

For the full year, the company lost $10.2 million, or 15 cents per share. In 2009 it lost $23.9 million, or 35 cents per share. Its revenue fell 5 percent, to $310.7 million from $327.1 million.The company said its total sales fell short of expectations for the year, and that revenue growth will be its biggest priority going forward.

Affymetrix shares fell 6 cents to $4.96 Wednesday. The stock rose 12 cents to $5.08 in after-hours trading.