The ratings of three life science stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Fluidigm Corporation (FLDM) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Fluidigm develops, manufactures, and markets proprietary Integrated Fluidic Circuit systems. In Portfolio Grader’s specific subcategories of Earnings Revisions and Equity, FLDM also gets F’s. As of Jan. 22, 2015, 11.2% of outstanding Fluidigm Corporation shares were held short. To get an in-depth look at FLDM, get Portfolio Grader’s complete analysis of FLDM stock.

Slipping from a C to a D rating, BG Medicin (BGMD) takes a hit this week. BG Medicine develops and markets diagnostic tests. The stock gets F’s in Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of BGMD stock.

The rating of Compugen (CGEN) slips from a C to a D. Compugen focuses on the therapeutic proteins and monoclonal antibodies to address unmet needs in the fields of immunology and oncology. The stock also gets an F in Equity. To get an in-depth look at CGEN, get Portfolio Grader’s complete analysis of CGEN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.