A rapid spot test for urinary methylmalonic acid collected on ion-exchange filter paper

We developed a rapid, accurate method to detect pathologic amounts of methylmalonic acid (MMA) in urine samples, which can be applied to simplify and improve the accuracy of screening for methylmalonic acidemia. Urine is collected on DEAE-cellulose paper and air-dried. Six mm discs are punched from the dried paper and placed in a multi-well tray; non-anionic substances interfering with the assay are rinsed from the discs; and a color reaction using diazotized p-nitroaniline is carried out in situ on the disc. Of 407 urine samples blindly tested, all 83 samples from nine patients with methylmalonic acidemia gave positive results. None of the other urine specimens from normal individuals or patients with a variety of organic acidemias gave positive results. This method should allow accurate and inexpensive mass screening for methylmalonic acidemia in newborn or infant screening programs.