The company said that diagnostic testing volumes, product and royalty revenues, and clinical services revenues all fell year over year.
The improvement in the 360Dx Index was modest compared to 2017, but it still outpaced the broader markets, which fell dramatically in the last month of the year.
The firm said clinical services revenues fell during the quarter due to reduced insurance reimbursement payments and mix of testing in the prior year.
Just five of the 28 firms in the 360Dx Index saw their share prices rise last month. Veracyte led the gainers, while Accelerate Dx had the sharpest decline.
The firm said the decline in Q4 revenues was due to an account loss as well as lower insurance reimbursement and shifts away from high-value genetic testing.
Natera, Invitae, and Opko Health were the biggest gainers in the 360Dx Index last month, while Enzo Biochem had the steepest decline.
Month over month, the 360Dx Index beat the Dow Jones Industrial Average, the Nasdaq Composite, and the Nasdaq Biotech Index.
The firm said that the decline was due to a customer shifting to internalizing genetic ordering, adverse weather, and the loss of an undisclosed commercial payor.
Seventeen of the 25 companies in the 360Dx Index saw their shares decline last month. Invitae paced the decliners, while GenMark led the gainers.