The technique comprises administration of the dye, determination of the interval before it appears in the urine, and the amount then excreted during definite periods. The dye is employed in solution, and is conveniently purchased already sterilized in ampules, each containing slightly more than 1 cc. of a solution of its monosodium salt of the strength of 6 mg. per cc. The patient drinks 200-400 cc. water, and 6 mg. of the dye are injected intramuscularly (lumbar muscles), or intravenously, 20 minutes later. The bladder is immediately emptied, and the urine discarded. The succeeding portions of urine may be collected by voiding, but it is more accurate to catheterize the bladder or ureters, and catheterization is practically a necessity for determination of the “appearance time.”
The appearance time is the interval of time elapsing between injection of dye and its appearance in the urine. It is determined by allowing the urine to drip from the catheter into a receiver containing a drop of 10% NaOH. The first traces of the dye will cause a pink color.
The time interval chosen for calculating excretion is then computed from the instant of this appearance. There is considerable diversity in practice as regards this time interval, and it would seem that shorter intervals and quicker results are gaining in preference, as well as being considered equal in value to longer periods.
The percentage excretion of the dye is now measured in each sample of urine. To do this, prepare a standard solution, made by diluting 0.5 cc. of the phenolsulphonephthalein solution mentioned above to about 200 cc. with water, adding 5-10% NaOH until no further intensification of the red color is produced (requires a few cc.), diluting to one liter, and mixing. This standard then represents 50% (3 mg.) of the amount of the dye injected. The color of the urine sample is similarly developed with alkali, and the mixture diluted to 1 liter, mixed, and compared with the standard in a colorimeter. The per cent excretion in the specimen equals the reading of the standard solution multiplied by 50 and divided by the reading of the urine mixture, when the colors are matched in the instrument.
For accurate work, it is desirable to balance in the standard the urine color of the unknown, and this is accomplished by including in the standard a volume of urine (dye-free) proportional to that in the unknown. Also, with a low excretion, it is better not to dilute the unknown to 1 liter, but to some lesser volume that will give a tint closer to that of the standard, and then allow for the variation in the calculation.
Fig. 153.—Fibres, starch granules, etc., which may be found in urine sediment. No. 12 gives appearance under microscope of scratches on old used glass slides. No. 15 (a), Tyroglyphus longior a mite. No. 15 (b), Trichomonas vaginalis. No. 16 (a), Egg of Eustrongylus; (b), Echinococcus hooklets; (c) Schistosoma egg; and (d), Filaria bancrofti embryo.
Dunning has devised a simple, inexpensive colorimetric outfit with permanent standards in ampules for this test. It is satisfactory unless the colors of the standards fade.
After intravenous injection, the normal appearance time is 4-6 minutes, and the normal elimination is 35-40% in 15 minutes, and totals of 50-65% for 30 minutes and 65-80% for 60 minutes; or, for the first 30 minutes, it may be stated as about 1% per minute from each kidney.