Protein Nitrogen Unit
Encyclopedia
The protein nitrogen unit (PNU) measures the potency of the compounds used in allergy skin test
s, and is equivalent to 0.01 microgram
(µg) of phosphotungstic acid
-precipitable protein nitrogen.
According to Russ Rowlett at the University of North Carolina at Chapel Hill
,
Skin allergy test
Skin allergy testing is a method for medical diagnosis of allergies that attempts to provoke a small, controlled, allergic response. -Process:A microscopic amount of an allergen is introduced to a patient's skin by various means:...
s, and is equivalent to 0.01 microgram
Microgram
In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used...
(µg) of phosphotungstic acid
Phosphotungstic acid
Phosphotungstic acid , tungstophosphoric acid , is a heteropoly acid with the chemical formula 31240. It normally present as a hydrate. EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly...
-precipitable protein nitrogen.
According to Russ Rowlett at the University of North Carolina at Chapel Hill
University of North Carolina at Chapel Hill
The University of North Carolina at Chapel Hill is a public research university located in Chapel Hill, North Carolina, United States...
,
Unfortunately, the potency measurements depend on the technique of measurement used, so results of one manufacturer are not comparable to those of another manufacturer. As a result, although PNU's are still used, they are being replaced by bioequivalent allergy units (BAU), which are measured by actual skin testing using reference preparations of standard potency.