The Sensex at the Bombay Stock Exchange lost 45 points, or 0.3 percent, to 15,836, on Thursday, ahead of the Reserve Bank's monetary policy review, and amid weak Asian markets. The Nifty at the National Stock Exchange lost 17 points, or 0.4 percent, to 4,746.Stock markets in Japan, China, Hong Kong, South Korea and Singapore dropped between 1.5 percent and 2 percent.