B vitamin deficiencies can cause a range of serious health effects, including spinal defects in children born to women with below-normal levels of folic acid and anemia in people not getting enough B12.

That’s why a two-step method of diagnosing those deficiencies that three medical school doctors patented in 1990 has become so widely used. It’s performed tens of millions of times a year, at a cost of just a dollar or two, by laboratory testing companies nationwide.