The salient feature of the table is, however, the fact that in early interstitial nephritis the retention of uric acid precedes that of urea or creatinine.
Its importance resides in the reflection that it lends support to those who contend that renal change, leading to failure of excretion of uric acid, is the primary cause of gout; in other words, it gives colour to Magnus Levy’s contention that the phenomena of gout are referable to “a deficient and restricted secretory power of the kidney.” The existence of such a selective excretory incapacity, i.e., for uric acid, does not, he considers, predicate a genuine nephritis. He maintains that such disability on the part of the kidney for uric acid excretion may exist without morphological change; in other words, he thinks it conceivable that a single function of the kidney can become almost exclusively insufficient, though later real damage to the organ and a nephritis frequently follow.
Reflecting on the above theory, it is obvious that, if carried to its logical conclusion, it would appear to postulate that gout is nothing more than a form of renal disorder, marked simply by functional inability to excrete uric acid. The postulate is no mean one, for, as Sir Archibald Garrod says, “If the fault is in the kidneys alone, gout must be removed once and for all from the category of metabolic disorders, and placed among the sequelæ of renal inadequacy, at least in so far as the uric acid phenomena of the disease are concerned.”
Furthermore, Levy’s hypothesis involves the assumption that the excreting functions of the kidney for uric acid and urea are separate and independent of each other, and to discussion of this we now pass on.
The Relationship, if any, between the Amounts of Uric Acid and of Urea, and Total Non-Protein Nitrogen in Human Blood
Taking samples of human blood from (1) unselected insane subjects and (2) chronic nephritics, Folin and Denis determined the amounts therein of urea, total non-protein nitrogen, and uric acid. The figures obtained showed that “there is apparently no relationship between the amount of uric acid and the amount of urea or total non-protein in nitrogen, in human blood.”
That such a discrepancy should obtain is doubtless of profound though as yet imperfectly grasped significance. These authorities rightly assume that, since the kidney is practically the sole avenue for nitrogenous waste excretion, it follows that the urea and total non-protein nitrogen of the blood must in the main be inversely proportional to the general efficiency of the renal organs. Then, obviously, the same law, too, should, in lack of some other plausible explanation, govern the excretion of uric acid also. But, as the above generalisation portends, it is apparently not so.
Fortunately, Folin and Denis prosecuted their study still further, taking in examples of gout (with and without clinically recognisable nephritis), also instances of leukæmia and lead poisoning.
The blood, again, in these disorders betrayed the same peculiarity, viz., that while containing an excess of uric acid, it did not contain correspondingly large amounts of urea or other waste nitrogen; in other words, the findings in the blood in gout were in full accord with the above generalisation, i.e., the apparent lack of any relationship between the amount of uric acid and that of urea or total non-protein nitrogen in the blood.