Convert NSInteger into NSString

This is my sample code to convert a integer into string.

Is it very costly to do the multiple loops of [NSMutableString stringWithFormat:..]?

I.e should I just use appendString and get the NSString in reverse order and then do one for loop to reverse this "reverse string".

Is there any other faster/more elegant way?

NSString * intToString(NSInteger numberToConvert)
{
    BOOL isNegative = (numberToConvert < 0);
    if (isNegative)
    {
        numberToConvert = -1*numberToConvert;
    }

    NSMutableString *convertedString = [[NSMutableString alloc] init];

    while(numberToConvert != 0)
    {
        convertedString = [NSMutableString stringWithFormat:@"%ld%@",numberToConvert%10,convertedString];
        numberToConvert = numberToConvert/10;
    }

    if (isNegative)
    {
        convertedString = [NSMutableString stringWithFormat:@"-%@",convertedString];
    }

    return convertedString;
}