undetermined nitrogen

un·de·ter·mined ni·tro·gen

the nitrogen of blood, urine, etc., other than urea, uric acid, amino acids, etc., that can be directly estimated; in blood it amounts to about 25 mg per 100 mL.

un·de·ter·mined ni·tro·gen

(ŭn'dĕ-tĕr'mind nī'trŏ-jĕn)
The nitrogen of blood, urine, and other fluids, other than urea, uric acid, amino acids, and the like, which can be directly estimated; in blood it amounts to about 25 mg per 100 mL.