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

This week, Enzo Biochem, Inc. (ENZ) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Enzo Biochem researches, develops, and manufactures health care products based on molecular biology and genetic engineering techniques. In Portfolio Grader’s specific subcategory of Equity, ENZ also gets an F. To get an in-depth look at ENZ, get Portfolio Grader’s complete analysis of ENZ stock.

The rating of BG Medicin (BGMD) slips from a C to a D. 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.

Luminex Corporation (LMNX) earns a D this week, falling from last week’s grade of C. Luminex develops, manufactures and markets biological testing technologies with applications throughout the clinical diagnostic and life science industries. The stock also gets an F in Earnings Revisions. As of Sept. 4, 2015, 10.1% of outstanding Luminex Corporation shares were held short. To get an in-depth look at LMNX, get Portfolio Grader’s complete analysis of LMNX 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.