The company expects EPS to be between $4.02 and $4.12. On a non-GAAP basis, EPS is expected to be in the range of $4.75 and $4.85.
The company attributed the lower revenue growth to lower volume growth in diagnostics, which is expected to continue for the rest of the year.
For 2018, Quest lowered its revenues expectation to $7.57 billion, its EPS to greater than $5.34, and its adjusted EPS to greater than $6.30.
The company said testing services revenues more than doubled during the quarter as its AlloSure kidney transplant diagnostic continued to penetrate the market.
MDx revenues increased 3 percent to $158.0 million, but excluding non-recurring royalty revenue in the prior-year period, MDx revenues increased 10 percent.
The company said its molecular collection systems products saw the highest revenue growth during the quarter as product revenues rose 6 percent overall.
Myriad CEO Mark Capone said earnings during the quarter exceeded expectations based on strong volume growth from hereditary cancer and new products.
Total revenues were down due to lower assay revenues, which shrank 11 percent from a year ago. Sample-to-answer molecular product revenues grew 15 percent.
The firm beat Wall Street analyst estimates for revenues and earnings per share in the third quarter.
Test volume for the firm's Cologuard colorectal cancer screening test rose 49 percent year over year during the quarter.