Article · Wikipedia archive · Last revised Jul 24, 2026

Protein nitrogen unit

The protein nitrogen unit (PNU) measures the potency of the compounds used in allergy skin tests, and is equivalent to 0.01 microgram (μg) of phosphotungstic acid-precipitable protein nitrogen. Potency measurements depend on the measurement technique, so that results from different manufacturers cannot be reliably compared: as a result, PNUs are being replaced by bioequivalent allergy units (BAU), which are measured by skin testing using reference preparations of standard potency.

Last revised
Jul 24, 2026
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The protein nitrogen unit (PNU) measures the potency of the compounds used in allergy skin tests, and is equivalent to 0.01 microgram (μg) of phosphotungstic acid-precipitable protein nitrogen.1 Potency measurements depend on the measurement technique, so that results from different manufacturers cannot be reliably compared: as a result, PNUs are being replaced by bioequivalent allergy units (BAU), which are measured by skin testing using reference preparations of standard potency.2

Notes

Notes

  1. May, JC; Sih, JT; Best, J; Douglas, G; Rancour, JM; Renker, HR; Spingola, F; Van Daele, L; Zudeck, S; et al. (November 1981). "Protein nitrogen unit precipitation procedure for allergenic extracts: collaborative study". Journal of the Association of Official Analytical Chemists. 64 (6): 1435–8. doi:10.1093/jaoac/64.6.1435. PMID 7309663.
  2. Ross, Rowlett (2002). "P". How Many? A Dictionary of Units of Measurement. University of North Carolina at Chapel Hill. Retrieved 2009-02-05.