U.S. stock index futures held their losses Tuesday despite a better-than-expected S&P Case-Shiller home price report, as investors remained cautious ahead of Fed Chairman Ben Bernanke's speech later this week.

On the economic front, home prices rose in June for the fifth month in a row, with the the S&P/Case Shiller composite index climbing 0.9 percent. Economists had expected a reading of 0.5 percent.