This should work. I would trim the whitespace from the input field first of all:
if($('#Field').val() != "") {
var value = $('#Field').val().replace(/^\s\s*/, '').replace(/\s\s*$/, '');
var intRegex = /^\d+$/;
if(!intRegex.test(value)) {
errors += "Field must be numeric.<br/>";
success = false;
}
} else {
errors += "Field is blank.</br />";
success = false;
}