1019 UREA-CONCENTRATION TEST. To the Editor of THE LANCET. SIR,-Having been away on holiday I have only seen a letter in your issue of May 6th from Prof. Hugh MacLean and Dr. 0. L. V. de Wesselow, referring to In an article of mine in THE LANCET of April 22nd. that letter they say :-
just
" Obviously, he (Mr. Kidd) is not quite certain whether or not he is right in his contention that the test was employed before we introduced it, for he states (quite wrongly as it the test, but I happens) thatMacLean says he introduced " do not feel convinced of this statement.’
On this question of fact I can only reply by quoting the exact words that anyone can read by opening Prof. MacLean’s book " Modern Methods in the Diagnosis and Treatment of Renal Disease " at They are as follows :p. 53. " The Urea-Concentration Test.-This test was introduced few years ago by MacLean and de Wesselow, and has given very good results."
a
Nothing could be clearer than that, and all
fairto the conclusion that Prof. MacLean did say that he introduced the test. I will now return to the point that needs discussionnamely, the question of priority. I raised the point as I think it is one that is worthy of discussion, being one that has been raised before, notably by Sir John Thomson Walker last year at a discussion at the Medical Society of London on Renal Function Tests. I will give the two tests, McCaskey’s and MacLean’s, in the actual words of the authors. McCaskey writes, Medical Record, March 21st, 1914 :" Method.-About 6 A.M. the bladder is emptied. Two hours later the urine is collected, and at the same time the
minded readers must
patient is given 30 g. of Just before taking the
come
urea, dissolved in 4 or 5 oz. of water. urea, the patient drinks one-half of
of thin cereal gruel, taking the other half after the urea. No other breakfast. The urine is then collected every two hours for 12 to 24 hours, the urea determined for each two-hour period, including the two hours preceding the ingestion of -the urea, and from these data the curve of excretion is constructed."
about 6
shows in his charts that the most marked period of excretion is usually, but not always, during the few hours following the urea meal, and specificially refers to it on p. 511 of his article as the highest bi-hourly output and as one of the three points to be attended to in studying the effect of forced elimination of preformed urea, and in various other passages which can best be summarised by quoting his conclusion No. 4 :urea
oz.
immediately
"
This differentiation can best be determined by surcharging the blood with the different substances in question and determining the rate of excretion of each, first over a brief period of time, 1chile the blood remains heavily surcharged, and again over a longer period to determine the duration of time required to depurate the blood of a morbid excess."
MacLean takes
advantage
of this
point
to
simplify the
test, and contents himself with measuring the amount and percentage of urea excreted or concentrated " during the two- or three-hourly periods which follow "
the urea meal and interpreting it by the rise of urea excretion or concentration to over 2 per cent. in one of these periods. The chief difference, then, seems to be that McCaskey talks of urea fed artificially into the blood through the mouth as being excreted by the kidney, whereas MacLean calls the process of excretion, concentration. The actual process carried out by the kidney is the same whatever the process is called,’ and this process is tested in the same manner by both workers, though MacLean places a different construction on his results. McCaskey lays stress on three points in estimating the results of his test, one of which he calls the highest or maximal bi-hourly output. MacLean only lays stress on one point-namely, the maximal percentage of urea excreted, or, as he calls it, concentrated, in the first two- or threehourly periods. This is in reality exactly the same point that McCaskey stresses in his maximal twohourly output, save that he takes a two-hourly period of excretion or concentration rather than an hourly period. The difference between the two tests is that McCaskey’s is likely to be more accurate as it considers three factors, whereas MacLean’s test is easier and quicker to perform as it only considers one factor, but for that reason it is more open to error ;and as McCaskey shows in some of his charts, the period of maximum output or highest concentration may not always occur during the first four hours but somewhat later, so that MacLean’s method of testing may sometimes miss this point. I am, Sir, yours faithfully, FRANK KIDD, M.Ch. Harley-street, W., May 15th, 1922.
book, p. 53 :Urea-Concentration Test.-It is carried out as follows The patient is asked to empty the bladder, and immediately afterwards he receives by mouth 15 g. urea dissolved in about 100 c.c. of water. The bladder is emptied one hour and two hours after the urea has been given and the specimens of urine examined for urea content. Thus if urea is given at 10 A.M. a specimen of urine is obtained at 11 A.M. and at 12 A.M. If either specimen gives a percentage of urea above 2, the kidneys are held to be fairly efficient ; the higher the concentration the more effective is the renal function. The reason why two specimens are taken is, that in certain MOROCCO BOUND. patients the urea given by mouth may produce a diuresis which tends to dilute the urine passed during the first hour. To the Editor of THE LANCET. In this case the second hour’s specimen should be examined. i Indeed, in routine work it is generally best to discard the ’I, SIR,-May I crave a space in your columns for an first specimen altogether, and to rely on the result obtained ’i announcement which reaches me from my friend Dr.. from the second specimen. Not more than about 120 c.cm. Gardette, editor of La Presse Thermale et Climatique, urine should be passed in the second hour. Occasionally, two voyages for medical men which he is if there is much available fluid in the patient’s system, it concerning to the Moroccan coasts for the late autumn ? may be necessary to take a specimen after three hours, or organising even to repeat the test, but this is seldom necessary. In The first starts from Bordeaux on Sept. 20th and patients with marked diuresis this must be allowed for in returns to Marseilles on Oct. 22nd. The second starts from Marseilles on Oct. 19th and returns to Bordeaux estimating the renal function." MacLean writes in his
"
.
Should MacLean’s test then be considered a new test which he has introduced, or should it rather be considered a test which was adopted from Albarran by McCaskey and others, and which has been simplified and improved by MacLean and his fellow-worker ? Both workers set out to test the effect on the kidneys after feeding patients with urea artificially by the mouth ; McCaskey uses 30 g. in 4 or 5 oz. of water ; MacLean uses 15 g. in about 100 c.cm. of water. In both cases the effect on the kidneys is judged by estimating the amount and percentage of urea subsequently excreted in certain periods by the mouth. McCaskey talks of excretion or elimination and maximal output, MacLean talks of concentration. McCaskey’s test is longer and more laborious as he measures the quantity and percentage of urea excreted during two-hourly periods for 12 or 24 hours, but he
Nov. 23rd. The accommodation both in transport and sojourn will be what is known as first class, and there will be no tips. The price for a medical man is 4750 francs (about £95), and for an accompanying wife or daughter 4950 francs (about £100). Furtherdetails may be obtained from Dr. Gardette, 3, rue on
Humboldt, Paris. I
am,
Sir.
yours
faithfully,
LEONARD WILLIAMS. Harley-street, W., May 10th, 1922.
THE annual
meeting
of
the
supporters of the-
Children’s Country Holidays Fund will be held on Saturday, May 27th, at 3 P.M., at the Whitehall Rooms, New Metropole Hotel, Northumberland-avenue, when the Countess of Athlone will preside, and Lord Finlay, the Rev. H. R. L. Sheppard, and Dame May Whitty will address the gathering.-