In chyluria the morning urine is often clear while that at night is milky. On standing, chylous urine separates into an upper cream-like layer with a pinkish sediment and, between, a pinkish-white fluid in which floats a clot. Filarial embryos may or may not be found.
Kidney Function and Its Determination
The ability of the kidney to excrete substances from the blood stream is frequently affected by disease, especially such as disturbs the kidney, and is usually diminished after the age of 50 years. Disease of the kidney, however, does not necessarily imply an inability to eliminate substances—the functional need not parallel the anatomical lesion. Function may be normal especially when the changes are of focal type.
Impairment of renal function does not affect the excretion of different compounds to the same extent. It is well established that functions for chlorides and for urea are independent of each other. In any urinary examination, then, one should bear in mind the possible effect of an impaired excretory power relative only to the substance under consideration. In this connection, we speak of the kidney threshhold for a substance, i.e., the concentration required in the blood stream before the kidney will excrete it, at least in abnormal amounts. For chlorides, this is quite definite at 562 for blood plasma; for sugar, it is about 160-180 for whole blood. The threshold is not necessarily absolute, but simply indicates that with less sugar, for instance, only the normal traces will be passed. Chloride excretion begins only when their concentration passes the threshold value, and the rate of elimination depends upon their excess. Other compounds, such as urea, for example, may have no definite threshold value. Disease may affect the value, either by raising it and causing abnormal retention, or by lowering it and giving rise to depletion.
We can establish the status of the renal function in any given case, and are then in a position to intelligently prescribe dietetic and other treatment. Chemical analysis of the blood indicates the metabolic products affected and guides us in the adjustment of the diet, etc., to the excretory powers of the kidneys. One must, however, not overlook the nutritive needs of the body.
Many methods are employed for the determination of kidney function, and their relative values are still debatable. Probably those least open to criticism are chemical analysis of the blood, the phenolsulphonephthalein test, and Mosenthal’s method. Ambard, McLean, Van Slyke, and others have devised formulae to this end, based upon chloride, urea, or sugar excretion, which have many warm advocates as well as severe critics. A rough clinical comparison of the two kidneys may be obtained by determining the urea in specimens of urine simultaneously collected by the ureteral catheter.
Blood Chemistry, now that its value has been established, is generally given preference and allowed greater weight in case of disagreement with other tests. It measures excretory function for normal metabolic products, and has the additional value of an aid in diagnosis and prognosis and a guide to treatment, especially dietetic. It has the disadvantage of a possibly unfamiliar technique, and does not afford a comparison of the two kidneys.
The substances usually considered are the nitrogenous compounds (nonprotein nitrogen, urea nitrogen, uric acid, etc.), but retention of others (sugar, chlorides, cholesterin, etc.) are also of significance in this connection. Of the nitrogenous constituents, the kidney excretes creatinine most readily, urea next, and uric acid with the most difficulty. As a consequence, an impairment of function results first in the retention of uric acid, then urea, and, finally, creatinine is also retained. Owing to the relatively small amounts of uric acid and creatinine present, the nonprotein nitrogen, which includes the nitrogen in them as well as in other compounds, is not appreciably affected except by the urea increase. This is the basis of an intelligent interpretation of the findings. The urea and nonprotein nitrogen are so markedly affected by diet, especially among nephritics, that judgment must be exercised when they are employed as indices of renal function. This fact was not properly appreciated until recently, and probably accounts for much of the discredit cast upon blood chemistry in this connection. The uric acid, being less exogenous in origin, is perhaps the most delicate and the safest index; the increase appears early, and 3.5 may be considered the high normal value. On the usual restricted hospital diet, over 20 for urea nitrogen should be considered suggestive of impaired kidney function; over 75 speaks decisively for renal involvement and probably uraemia.
Phenolsulphonephthalein (Phthalein, or Red) Test.—This was developed by Rowntree and Geraghty, and its simplicity makes it very useful, especially to the isolated practitioner with limited laboratory facilities. It estimates only function for a foreign substance, is not considered quite as reliable as chemical analysis of the blood, and, of course, does not give the additional information that the latter supplies. It is, however, of much value, has no contraindications, and does compare the kidneys when combined with ureteral catheterization or use of a separator. Positive results are of more significance than negative, and it is less affected by glomerular than tubular changes. Values of more than 75% for 2 hours may be accompanied by diuresis, and Frank considers such a finding suggestive of renal disturbance with irritation if there is any corroborative evidence.