It is a well-known fact that the ordinary tests for urinary proteins, especially for serum proteins, are not specific. Several concordant tests are necessary for satisfactory differentiation. Reliance on a single test often leads to error; a disturbing factor may prevent the detection of a substance that is present or may simulate the behavior of a substance that is absent. It is the object of this paper to present some observations on a disturbing factor in Heller's test.
The tests most frequently used by the general practitioner for the detection of serum protein in the urine are: (1) The heat test—coagulation by boiling aided by a slight proportion of acid; (2) precipitation by potassium ferrocyanid in the presence of acetic acid, and (3) Heller's test—precipitation by concentrated nitric acid.
As stated above, none of these reactions is specific for any of the serum proteins, the proteins in the urine about