Nasdaq told the company that its shares have failed to meet a minimum $1 per share closing price for 30 consecutive days and may face delisting action.
Other big gainers last month included Accelerate Diagnostics and Natera, and share prices of 23 of the 27 companies in the index increased month over month.
The firm said it needs more time to ensure that the DetermaVu assay is providing the most consistent and sensitive results for patients.
The investment bank gave Danaher a Neutral rating and a $148 price target on the firm's shares, while it gave Agilent an Overweight rating with an $83 price target.
The broader market drove down the stock prices of many diagnostics companies. Natera, Guardant Health, and CareDx paced the gainers.
The number of gainers outpaced decliners 21 to six, and the index outpaced the Dow Jones Industrial Average, the Nasdaq Composite, and the Nasdaq Biotech.
Many diagnostic firms saw gains in their stock prices last month as Invitae and NantHealth also saw healthy increases.
The 360Dx Index was up 12 percent last month as shares of Accelerate Diagnostics, Veracyte, and Exact Sciences each improved more than 40 percent month over month.
With its stock price languishing below $1, NantHealth has 180 days to come into compliance with Nasdaq listing rules.
UBS initiated coverage of Quest with a Neutral raing and a $90 price target on its shares. It gave LabCorp a Buy rating and a $169 price target.