Tucson-based Accelerate Diagnostics Inc. said today it will raise $20 million by offering existing shareholders rights to buy additional shares of its stock.

The company, which moved to Tucson earlier this year from Denver, develops systems designed to rapidly diagnose drug-resistant and hospital-acquired infections.

Accelerate announced it has registered the offering with the U.S. Securities and Exchange Commission but said it has not determined the price or date of the offering. It said Abeja Ventures, a firm whose owners include four Accelerate directors, has committed to buy any shares that aren’t sold.

Shares of Accelerate Diagnostics closed down 32 cents, or more than 3.5 percent, at $8.44 in trading today on the Nasdaq Stock Market. The company's stock has traded in a range of $2.55 to $8.99 over the past year.