Enough B12? No, there is no easy way to know. The symptoms of deficiency are many and very diverse and overlap with symptoms of other health problems, and the blood test for vitamin B12 is not a reliable indicator. The most reliable test is urinary methylmalonic acid. If you have a B12 deficiency, the body’s ability to break down methylmalonic acid will be impaired, and the amount of that substance in your urine will be higher than normal.