Estimation of renal function utilizing the excretory urogram is generally unsatisfactory, except when judged from early films. By comparing the specific gravity of urine specimens obtained just prior to the administration of the contrast medium and prior to the postvoiding film, the radiologist could obtain an objective measure of renal function which would permit a more accurate interpretation of the urogram. The test is accurate and simply performed, requiring only a hydrometer and two specimen bottles. Neither accurate timing nor volume determinations are necessary. The referring physician could be provided with the radiographic findings and a quantitative measure of renal function at no additional expense to the patient.
Marshall S. Urinary Specific Gravity During Excretory UrographyA Test of Renal Function. JAMA. 1964;187(5):333–335. doi:10.1001/jama.1964.03060180019004
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