URINE 507 



Ordinarily 10 c.c. of urine is used in the determination by this method, but if 

 the content of creatinine is above 15 mg. or below 5 mg. the determination should 

 be repeated with a volume of urine selected according to the content of creatinine. 

 This variation in the volume of urine according to the content of creatinine is quite 

 essential, since the method loses in accuracy when more than 15 mg. or less than 

 5 mg. of creatinine is present hi the solution of unknown strength. 



Calculation. By experiment it has been determined that 10 mg. of pure crea- 

 tinine, when brought into solution and diluted to 500 c.c. as explained in the above 

 method, yields a mixture 8.1 mm. of which possesses the same colorimetric value 

 as 8 mm. of a N/2 solution of potassium bichromate. Bearing this hi mind the 

 computation is readily made by means of the following proportion in which y repre- 

 sents the number of millimeters of the solution of unknown strength equivalent to 

 the 8 mm. of the potassium bichromate solution : 



y : 8.1 : : 10 : x (mg. of creatinine hi the quantity of urine used). 



This proportion may be used for the calculation no matter what volume of 

 urine (5, 10, or 15 c.c.) is used in the determination. The 10 represents 10 mg. of 

 creatinine which gives a color equal to 8.1 mm., whether dissolved hi 5, 10, or 15 c.c. 

 of fluid. 



Calculate the quantity of creatinine in the 24-hour urine specimen. 



Interpretation. The daily excretion of creatinine by an adult of 

 medium weight averages about ij^ grams. The value is nearly con- 

 stant from day to day for a given individual being influenced by the diet 

 hardly at all unless this contains much preformed creatinine (as in case 

 of a heavy meat diet) . The excretion of creatinine is to a certain extent 

 a measure of muscular efficiency and of the amount of active muscle 

 tissue in the body. Relative to body weight less creatinine is excreted 

 by obese persons. 



Creatinine excretion is decreased in disorders associated with mus- 

 cular atrophy and muscular weakness. It increases with increased 

 tissue cetabolism as in fever. 



By the " creatinine coefficient" is meant the number of milligrams 

 of creatinine nitrogen excreted daily per kilo of body weight. This 

 varies under normal conditions from 7-11. 



Use of Pure Creatinine Standards. Instead of using as a standard a potassium 

 dichromate solution as above indicated, a solution of pure creatinine is to be recom- 

 mended. By using this certain arbitrary factors are eliminated and the method 

 becomes of more general applicability. The standard need not be set at a definite 

 mark as is necessary in the case of dichromate and temperature and time have less 

 influence on the accuracy of the results. A stock solution of pure creatinine (made 

 according to Benedict's directions; see Chapter XXII on Physiological Constituents 

 of Urine) is made by dissolving i gram of the substance in sufficient N/io HC1 to 

 make a liter. This solution contains i mg. of creatinine per cubic centimeter. In 

 carrying out the determination treat 10 c.c. of the stock solution in the same way and 

 at the same time as the 10 c.c. sample of urine. Compare in the colorimeter. The 

 calculation s simple. The reading of the standard divided by the reading of the 



