The overall ratings of four life science stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, QIAGEN NV (QGEN) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Qiagen provides sample and assay technologies. The stock’s trailing PE Ratio is 36.90. To get an in-depth look at QGEN, get Portfolio Grader’s complete analysis of QGEN stock.

This week, Wuxi PharmaTech (Cayman) Inc. Sponsored ADR’s (WX) rating worsens to a D from the company’s C rating a week ago. WuXi PharmaTech operates as a pharmaceutical, biotechnology, and medical device research and development outsourcing company primarily in the People’s Republic of China and the United States. For more information, get Portfolio Grader’s complete analysis of WX stock.

This week, BG Medicin (BGMD) drops from a C to a D rating. BG Medicine develops and markets diagnostic tests. The stock gets F’s in Equity, Cash Flow and Sales Growth. To get an in-depth look at BGMD, get Portfolio Grader’s complete analysis of BGMD stock.

Bio-Techne Corporation (TECH) is having a tough week. The company’s rating falls from a C to a D. Techne develops, manufactures, and sells biotechnology products and hematology calibrators and controls. The stock has a trailing PE Ratio of 31.20. For more information, get Portfolio Grader’s complete analysis of TECH 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.