protocol for the NBT-PABA test

Last reviewed 01/2018

The NBT-PABA test of pancreatic exocrine function is performed in the following way:

  • the patient is fasted overnight
  • 500 mg NBT-PABA with 5 microCi C14-PABA in 25 g casein is given orally in 500 ml water
  • urine is collected for 6 hours
  • urine collection is analysed for PABA content and C14 radioactivity
  • the fractional excretion of PABA and C14 label is calculated

Interpretation of results:

  • the PABA excretion ratio is calculated by: PABA excreted/PABA ingested
  • the C14 excretion ratio is calculated by: C14 excreted/C14 ingested
  • the ratio of the PABA ratio to the C14 ratio:
    • exceeds 0.76 in normal individuals
    • is less than 0.76 in patients with exocrine pancreatic impairment