An important source of error in Heller's test for urinary protein

Abstract

Heller's test for urinary protein is a fairly reliable one if care is taken in its application, but several urinary protein constituents give uncertain results with it. Thus, mucin fails to yield true precipitation — the “ring” is more or less opalescent and disappears on mixing. With nucleoalbumin the ring is not quite typical and is indistinct in undiluted urine. On the other hand various misleading factors, such as resinous acids, must be taken into account. Resinous acids may be ignored, however, if such products as Balsamum Copaivae, or Santal Oil, have not been administered, or if the specific HCl test for resinous acids shows their absence. The turbidity formed with resinous acids dissolves on warming. The acids themselves may be removed by extraction with ether. In concentrated urine, as is well known, a uric acid ring may appear just above the line of junction of the urine and acid, and urea may be precipitated in the form of glittering nitrate crystals; but dilution of the urine prevents these effects.

In the course of our investigation of another problem, an additional source of error has been found in urines preserved with thymol in any of the usual ways. If Heller's test is applied to such urine after filtration, a ring will invariably appear even in the absence of protein. The ring is most marked, all other things being equal, in urines that have been treated with a solution of thymol, although it is very conspicuous in urines that have been preserved with powdered thymol.

The characteristics of this ring may be briefly stated as follows : A few seconds after the urine has been carefully poured upon the acid, there forms, precisely on the line of junction, a grayish white ring about 0.5 mm.