It is not sufficient to-day to be able to diagnosticate the presence of disease in any organ; we wish to know also to what extent the disease has interfered with the function of that organ.
The kidneys lend themselves particularly well to estimation of function on account of the ease with which their excretion can be obtained. It is for this reason that methods of estimating the functional ability of these organs have developed so rapidly and effectively. It is scarcely necessary to refer to the inadequacy of the most careful clinical examination of the patient, combined with the most thorough clinical and microscopic examination of the urine always to reveal the presence of kidney disease, even when it is far advanced. Again, when pathologic elements are present in the urine, the exact significance of these is not always evident. Abundant albumin and casts can be present when the renal lesions
GERAGHTY JT. A STUDY OF THE ACCURACY OF THE PHENOLSULPHONEPHTHALEIN TEST FOR RENAL FUNCTION. JAMA. 1913;60(3):191-194. doi:10.1001/jama.1913.04340030021012