The protein nitrogen unit (PNU) measures the potency of the compounds used in
allergy skin tests, and is equivalent to 0.01
microgram
In the metric system, a microgram or microgramme is a unit of mass equal to one millionth () of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom whe ...
(µg) of
phosphotungstic acid
Phosphotungstic acid (PTA) or tungstophosphoric acid (TPA), is a heteropoly acid with the chemical formula . It forms hydrates . It is normally isolated as the ''n'' = 24 hydrate but can be desiccated to the hexahydrate (''n'' = 6). EPTA is the nam ...
-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.
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Notes
Medical technology
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