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By GASPAR GRISWOLD, M. D., of New York County.
Read November 20, 1884.
UNDER the title of false albuminuria, this paper will include two distinct classes of cases :
1. Cases in which the urine does not contain albumen, but in which a precipitate resembling albumen is caused by the ordi
2. Cases in which albumen is actually present in the urine, but does not come from the kidney.
The detection of slight degrees of albuminuria is often more important in practice than the determination of larger quantities; for the cases in which the albuminuria is so ill-defined as to be doubtful are those in which dropsy and other characteristic symptoms are least marked and in which we are most dependent upon urinary analysis in making a diagnosis. It is very easy to determine the existence of renal disease, when the urine contains albumen and casts in abundance and the patient presents the familiar dropsical appearance; but when there are no symptoms beyond a somewhat persistent headache with restlessness and occasional digestive disturbances, just enough to suggest the possibility of kidney-trouble, it becomes a very difficult problem to determine the importance of a faint trace of albumen in the urine. We ascertain the specific gravity and the quantity passed. Both are not far from normal. In such a case, we then examine carefully for casts, but very rarely find them, for, even if they be present, they are usually so few that it is a matter of remote chance to hit upon one. While the discovery of casts is conclusive evidence that the kidneys are affected, the failure to find them certainly can not be taken as proof that the kidneys are sound. This brings us face to face with the question whether, the urine being normal in all other respects, we may not have been mistaken about the trace of albumen. The patient may be suffering only from dyspepsia after all, and the slight precipitate which we obtained may not have been due to albumen, but to some error in testing the urine. Or may not some peptone, imperfectly elaborated in the course of the indigestion of which the patient complained, have passed into the urine and given us a precipitate resembling albumen? Or, even further, supposing the precipitate to be albumen, may not the small quantity which we observed have come from some irritation of the bladder or prostate?
It is obviously of the greatest importance, as regards both prognosis and therapeutics, to be able to decide whether a slight cloudiness or deposit which occurs in a specimen of urine when tested is really albumen, and, if so, whether the albumen come from the kidney or not. In discussing these questions, only the tests with heat and nitric acid will be referred to ; but it will be assumed that, in all doubtful cases, scrupulously clean test-tubes are used, the urine filtered before testing, and the presence or not of a precipitate determined by looking through the urine at a black background in a good light. The accurate compliance with all these detailed requirements is absolutely essential, and no results are reliable in obtaining which they have been neglected.
The test spoken of in this paper as the “cold nitric-acid test” is performed as follows: Into a test-tube of small caliber is first poured one drachm of pure, colorless nitric acid. About one drachm of the suspected urine is then allowed to flow down the side of the tube, drop by drop, from a pipette, so as to float upon the nitric acid without mixing with it. If albumen be present, a sharp white band appears at the point where the acid and urine are in contact. This is often spoken of as Heller's test, and it is generally admitted to be the most certain and
satisfactory method of determining the presence of small quantities of albumen.
The substances which may precipitate so as to simulate the presence of albumen claim consideration first. They are phosphates, mucus, uric acid, peptones, and resinous drugs, like copaiba.
Phosphates.—The old familiar statement, that phosphates are precipitated when alkaline urines are heated, has done harm in making many forget that the same thing may occur with distinctly acid specimens. It frequently happens that urine which turns blue litmus red gives a precipitate on boiling, which disappears when a few drops of nitric acid are added. In such a specimen, if sufficient acid be added previous to boiling, to prevent the precipitation of phosphates, the precipitation of albumen may also be thereby interfered with ; for, in very acid urine, small quantities of albumen are often converted into acid albumen and will not then be precipitated on boiling.
The best test for urine which deposits phosphates on boiling, in spite of being acid, is the cold nitric-acid test. By this test the presence of albumen will be distinctly shown without any precipitation of phosphates to obscure it.
Mucus.—Normal urine often contains a considerable quantity of mucus, more or less dissolved at first, but separating as the urine cools, and producing a cloudy appearance. Mucus is not precipitated either by boiling or by nitric acid, and it therefore does not usually interfere with the tests for albumen. There are two exceptions to this rule: 1. When the urine is alkaline. 2. When so much mucus is present that the urine is too cloudy for a slight precipitate of albumen to be distinctly seen. Before discussing the first exception, it will be necessary to recall the fact that, if a small quantity of albumen be present in alkaline urine, it may be converted into alkali-albumen, and will not then be precipitated on boiling. If the specimen be first neutralized by adding to it a few drops of acetic acid, and then boiled, the albumen will be precipitated as usual. It is therefore necessary to neutralize alkaline urine before employing the heat-test for albumen; and it is further necessary that acetic
acid should be used for this purpose and not nitric acid, for the addition of a few drops of nitric acid previous to boiling will sometimes entirely prevent the precipitation of albumen, even in specimens which contain it in abundance. The writer has had under his care one case in particular of advanced Bright's disease with extensive dropsy and casts, in which the previous addition of a few drops of nitric acid prevented any precipitate on boiling, although the urine contained a large quantity of albumen. In this case, the presence of albumen was always plainly shown by the cold nitric-acid test or by boiling after neutralization with acetic instead of nitric acid. Now, if a specimen is to be examined which is alkaline and also contains mucus, a difficulty presents itself in the fact that acetic acid precipitates
If we boil the alkaline urine without neutralizing it, the albumen contained may not be precipitated. If we add acetic acid to neutralize the urine, the mucus may be precipitated so as to resemble albumen; and we can not neutralize the urine with nitric acid, because this again may prevent precipitation of the albumen. From these considerations it is evident that we can not depend upon the heat-test to show a small quantity of albumen in an alkaline urine which contains mucus. Under the circumstances, it is best to employ the cold nitricacid test, which precipitates albumen equally well in alkaline urine and does not precipitate mucus. Under the latter exception, when so much mucus is present that the urine is too cloudy for a slight precipitate of albumen to be seen distinctly, the mucus should be removed by the following process: Add two drachms of urine to an equal quantity of liquor potassæ in a test-tube, warm gently, and then filter. The fluid which comes through will be free from mucus and may be tested for albumen by the cold nitric-acid test. The writer has satisfied himself by experiment that the removal of mucus in this way does not interfere with the subsequent detection of small quantities of albumen. The experiment was as follows: In one test-tube were put, one drachm of an albuminous urine, one drachm of nonalbuminous urine cloudy with mucus, and two drachms of liquor potassæ; and the mixture was then warmed and filtered in the
manner described. Into another test-tube were then poured, one drachm of the same albuminous urine, one drachm of normal urine without mucus, and two drachms of water. Both testtubes, therefore, contained the same quantity of albumen and the same proportion of other constituents, the only difference being that the contents of one had been put through the liquor-potasse process for removing mucus, while the other had not. When these two specimens were subjected to the cold nitric-acid test, they each gave the same quantity of albumen-precipitate, showing that the mucus-removing procedures which one of them had undergone had not modified its subsequent reaction.
. Uric Acid.-If a specimen of urine contain uric acid or urates in considerable quantity, the following mistake may be made: A specimen of acid urine is boiled, and a few drops of nitric acid then added, without the appearance of a precipitate. The test-tube is put aside for perhaps tifteen minutes, and then looked at again and shaken. A precipitate may now be present, which may be mistaken for albumen. This is probably composed of urates and uric acid, which have been deposited as the urine cools, because the specimen has been rendered more concentrated by boiling and more acid by the addition of nitric acid. To settle the question, boil the urine again; if the deposit be albumen, it will remain unchanged ; if it be anything else, it will redissolve and disappear.
There is also a possibility of error when concentrated urine is tested by the cold nitric-acid method. In this case, a precipitate of uric acid and urates, somewhat resembling albumen, may form near the point where the urine and nitric acid are in contact. This is best avoided by diluting the urine with three or four parts of water before pouring it upon the acid. The urine will then no longer be concentrated enough to yield a precipitate of uric acid and urates, and the reaction for albumen will not be interfered with.
Peptones.--These more or less digested forms of albumen are often present in the urine, both in cases in which the urine also contains ordinary albumen and in cases in which it does not. True peptone, or completely digested albumen, is not precipitated