You could be incredibly specific about it:
var regex = new Regex(@"<span id=""point_total"" class=""tooltip"" oldtitle="".*?"" aria-describedby=""ui-tooltip-0"">(.*?)</span>");
var match = regex.Match(@"<span id=""point_total"" class=""tooltip"" oldtitle=""Note: If the number is black, your points are actually a little bit negative. Don't worry, this just means you need to start subbing again."" aria-describedby=""ui-tooltip-0"">31</span>");
var result = match.Groups[1].Value;