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The plasma phenolsulfonphthalein index (PSPI) was determined in 175 subjects and was compared with levels of blood urea nitrogen (BUN) and serum creatinine, 15-minute urinary excretion of PSP, and clearance of creatinine, PAH and inulin. Statistical analyses indicate that the PSPI measures the same function as the 15-minute urine test when PSP is administered in a dosage of 1 mg./kg. body weight; and that, although the index cannot be used as a precise substitute for PAH clearance, it is equally repeatable and no greater error is associated with its measurement. The PSPI has been found of most value when complete, accurately timed urine collections are unobtainable because of urological abnormality or inability of the patient to co-operate.

A comprehensive one-day renal function test consisting of a single outpatient visit lasting nine hours, with a minimum of time off work or away from home, is described in detail. Although a large number of laboratory tests are performed in one day, patients usually appreciate thoroughness, and the cost is more than offset by the saving in occupancy of hospital beds and by the early and precise diagnosis of reversible aspects of renal disease. Some aspects of improved methodology, such as the sequential determination of minimum urinary pH, bicarbonate, titratable acid, ammonium, and total acid on a single sample using an automatic titrator, are given in detail. Clinical application of the comprehensive nine-hour renal function testing system is illustrated by the result sheet of a patient with analgesic nephropathy, who was shown in one day to have secondary severe renal failure (glomerular filtration rate 20% of normal for age and surface area), renal tubular acidosis of the distal gradient type (minimum urinary pH 6.20), increased urinary white cell excretion rate, hyaline casts, and absence of red cell casts, consistent with a diagnosis of analgesic nephropathy and urinary tract inflammation. Normal values with 95% range for this laboratory are also given. This testing system has been found to be very useful in investigating patients with analgesic nephropathy, renal tubular acidosis, and after renal transplantation.