Gull Laboratories, 1011 E. 4800 South, a company that develops, manufactures and markets diagnostic kits for infectious disease detection, reports net income of $217,000 after taxes or 4 cents per share for the first quarter of 1991, an increase over the $70,000 net income or 1 cent per share in the same period a year ago.

Company officials reported first-quarter sales of $1.6 million, a 24 percent increase over the quarter a year ago.While the company had growth in all areas, the biggest growth occurred in the medical diagnostic products. Gull's major investments in product development and marketing in 1990 allowed the company to enter new segments of the immunodiagnostics market, company officials said.