CHAPTER II THE TESTS FOR ALBUMINS
Albuminous bodies do not occur in normal urine except, perhaps, in mere traces. Numerous investi- gations have been published on this subject, and while some of the recent ones would seem to show the prob- ability of a phystological albuminuria, others, seem- ingly as thorough, lead to quite the opposite conclu- sion.
Temporarily, it is true, albumin may be found in the urine of healthy individuals, as after the consump- tion of large quantities of egg albumin, or after the action of some cause producing a sudden altera- tion of the blood pressure, but the amounts found in such cases are too small, and their occurrence too rare, to permit them to be classed as anything but acci-
/dental. It is certain that the presence of any appre- , ciable amount of albumin in the urine and the per- | sistence of the same must be looked upon as a fatho- | logical phenomenon and one of the greatest impor- ‘tance to the physician.
Albumins may appear in urine from several sources, most frequently, probably, because of some structural change in the tubules of the kidneys which permits a filtration from the blood. But this is not always the case as they may appear from sources in no way de- pendent on renal disorder, from lesions of the ureters,
TESTS FOR ALBUMINS 17
bladder, or urethra, for instance, in which case blood or pus may be present. Ordinary serum albumin is the usual, but not the only proteid body which may appear in urine. Half a dozen or more modifications have been described as occurring under different cir- cumstances, but the evidence for some of these appears to be of doubtful character. Certain forms are not readily detected or identified. In what follows, tests will be given for those proteid bodies which can be detected with certainty and whose presence has some definite clinical importance.
- Serum Albumin
The presence of serum albumin in the urine is a characteristic of what is ordinarily termed albuminuria. | As intimated above albuminous bodies may appear in the urine from different sources. The presence of serum albumin suggests (a) a functional or structural disorder of some part of the essential tissue of the kid- ney, in which case we have renal albuminuria or true albuminuria, ot (6) a lesion of some part of the uri- nary tract below the kidney, in which case we have what is called false or accidental albuminuria.
Renal albuminuria is the condition appearing in Bright's disease or acute parenchymatous nephritis and in other pathological conditions in which a change of the diffusion membrane is involved. It is also fre- quently induced by derangements in the circulation due to heart diseases, high fevers, etc., which in turn may react and give rise to a derangement of the kid-
ney itself. That is to say, the causes producing cer- 2
18 URINE ANALYSIS
tain febrile conditions may extend to the structure of the renal filtering apparatus and so alter its condition that the passage of albumin is no longer hindered but becomes continuous.
Under all such circumstances the albumin passing through the kidney is generally accompanied with something which suggests its origin. There may be here an excessive amount of the epithelial lining of the tubules, or plugs of coagulated albumin, mucus, or of the wax-like, partially degenerated albumin known as lardacein, all in the form of “casts” of the uriniferous tubules. These may be readily seen and recognized by the microscope.
As intimated above, false or accidental albuminuria can originate from several causes and in general is a condition of far less clinical importance than the other. It is usually possible to determine by a few examina- tions the real nature of the disorder by aid of the facts just mentioned.
Because of the very great importance of the subject to the physician, much attention has been given to the question of albumin tests, and the number of re- actions proposed for its detection reach, possibly, the hundreds. Many of these are of such extreme delicacy and so easy of execution that to make a choice of a few is by no means a simple matter.
The best of them depend on the fact that the solu- ble serum albumin, which finds its way into the urine, can be eoagulated and made visible as white flocculi, or as a white cloud when present in small quantity. Of the various methods of producing this coagulation,
TESTS FOR ALBUMINS 19
only those will be mentioned which are most charac- teristic, and practically the most useful.
QUALITATIVE COAGULATION TESTS
Coagulation by Heat.—When a sample of urine is boiled, a precipitate usually forms. This in most cases consists of earthy phosphates, and is often sufficient to conceal a precipitation of albumin possibly present. If now to the boiled sample about one-tenth its vol- ume of strong—nitric acid be-added, | the precipitated ee _will -diseppear,-while the albumin will re- \
main-ceagtiated. It is necessary to add as much nitric } acid as is here indicated, because a small amount may sometimes dissolve coagulated albumin, forming solu- ble acid-albumin, This acid-albumin is broken up on the addition of more acid.
Even when boiling does not throw down a precipi- tate, the addition of nitric acid cannot be omitted, as under certain circumstances the heating may produce asoluble combination between alkalies present and albumin, which is stable. Nitric acid in sufficient quantity will break up this combination and bring about coagulation.
Under most circumstances this heat test, as outlined, is sufficient, and the possibility of making a mistake is very small. It is shown in works on chemical physi- ology that small amounts of albumin combine readily with weak acids and alkalies, forming soluble and stable combinations known as acid-albumin and alkalt- albumin,
If the urine has a neutral or alkaline reaction
20 URINE ANALYSIS
to begin with a small amount of alkali-albumin would escape detection by heating alone. On addition of just the proper amount of acetic acid to neutralize the alkali, the application of heat will cause a coagu- lation, but a slight excess of this acid might convert the a/kalt-albumin into actd-albumin, equally hard to precipitate. Traces of nitric acid, and in a marked degree hydrochloric acid, behave in the sane manner, but the addition of larger amounts of nitric acid is free from this objection because in proper amount this acid is able to decompose both acid- and alkali-albumin.
When taken for examination, urine is frequently cloudy from the presence of precipitated urates or earthy phosphates. Heat is sufficient to dissipate the cloud if due to the urates, but the phosphate cloud is rendered heavier. It is always a good plan to care- fully filter the urine, if in the least degree turbid, before undertaking the test.
With old samples of urine which have undergone the urea fermentation and have become alkaline, the test by heat and subsequent addition of acid is not always satisfactory or convenient. In such cases it is best to proceed at once to a inethod which disposes of the excess of alkali at the start, and in such a manner as to cause no confusion,
Coagulation by Nitric Acid.—As indicated above ni- tric acid can coagulate albumin, and this test is fre- quently employed without-previous boiling. When applied to fresh urine the test may be made in this manner.
Several cc. of the strong acid are warmed in a test-
TESTS FOR ALBUMINS 21
tube, and over this is carefully poured an equal vol- ume ime, so as to overlie without mixing. If albumin is present a white ring appears at the surface between the two liquids. When the urine contains an excess of coloring-matter the ring is variously tinted.
If urine is poured over cold acid, a precipitate may appear which is not albumin. This can happen when the urine is highly charged with urea, in which case crystalline nitrate of urea will separate out, or where urates are abundantly present, in which case the ring will consist of very fine crystals of uric acid, or acid urates. Both of these precipitates are dissi- pated by heat, and if the nitric acid is previously warined, they cannot appear. It is better to make the test as just suggested than to use cold acid, and then try to warm a ring formed, as this would cause an admixture of the liquids sufficient to obscure a slight amount of albumin.
It is sometimes recommended to pour the urine in a test-tube, and by means of a pipette, or dropping- tube, allow the acid to flow under it. This is an ex- cellent method of performing the test, but the acid should be slightly warm as before. If only a trace of albumin is present the ring will not appear immedi- ately, but only after standing. It is well, therefore, in doubtful cases, to set the tube aside for twelve hours and then observe it. If a ring is now found it should be very gently and carefully warmed to determine its behavior toward heat, because on standing in the cold a ring of urates might appear.
22 URINE ANALYSIS
When this test is applied to old, cloudy, or alkaline urine it should be preceded by this preliminary prep- aration:
Boil the urine with half its volume of ro per cent. potassium hydroxide solution and filter. This will usually give a bright, clear liquid, but if not, add two drops of the “magnesia mixture” employed in quali- tative analysis and described in the appendix, boil and filter again. The filtrate is now suitable for testing.
The action of the reagents is this: The strong al- kali formsa bulky precipitate of the earthy phosphates present which usually settles aud leaves the supernatant liquid clear. The amount of alkali taken is sufficient to prevent the coagulation and precipitation of the albumin on boiling, while it serves also to expel am- monia which may be present. If the first filtrate is not perfectly clear the addition of the magnesia mix- ture accomplishes this by making a new precipitate of phosphates in traces which now leaves it bright.
With the clear filtrate the tests by addition of nitric acid may now be carried out. It must be remembered, however, that as the urine is now strongly alkaline, a relatively large volume of the strong nitric acid must be employed. .
The text-books abound in minute descriptions con- cerning the best methods of conducting this compara- tively simple test. The few sources of error which may mislead will now be pointed out. It is, of course, understood that these appear only in the search for small amounts of albumin; that is, for amounts less than one-tenth of 1 per cent. by weight. For greater
TESTS FOR ALBUMINS 23
quantities the reactions, even when not conducted with extreme care, are usually sharp. .
When urine is poured over nitric acid or when the acid is introduced under the urine a ayer of some kind always appears at the junction of the two liquids. The problem is to decide what this is. The peculiar appearance of a relatively large amount of coagulated albumin is so characteristic that any one who has ever seen it will recognize it again. But a faint cloud or haziness is, at the start, somewhat confusing. A colored layer or ring, which is very common, must not be mistaken for a precipitate or cloud. The normal urine coloring-matters may produce a highly colored ring, and the bands with biliary colors are even deeper. But these color bands or zones are transparent which can be determined by holding the test-tube in the proper light.
Urine very highly charged with urea may give a crystalline precipitate of urea nitrate. This is a very unusual reaction, and the precipitate may be very easily recognized through the form and size of the crystals, which are large flat plates readily seen by the naked eye or by a common magnifying lens. Ifa urine suspected to contain such an excess of urea be diluted with an equal volume of water before testing the crystals will not appear. Besides, they do not appear when the liquids are warm. The finely gran- ular precipitate of acid urates or hydrated uric acid appears only in a cold liquid, therefore cannot be present to mislead if the test is conducted as directed.
If the special tests indicate the presence of unusually