Not able to pass the 'single value drop down' list value through the URL and filter is not working! please help! it's very urgent!

I am able to pass the filter value from multi value drop down list in the URL followed by "?Region=USA" successfully, but when I try to pass the value from single value drop down list, It's not getting filtered ex - "?Region=USA&Indication=Other" , where Indication values are present in single value drop down list.