Since the first report1 of the rapid excretion of phenolsulfonphthalein (PSP) or phenol red by the kidney, PSP has been used widely to assess renal function, without serious mishap.2 Use of the intravenous route and earlier measurement of excretion (starting at 15 minutes) have enhanced the value of the test. The mechanism of tubular excretion of PSP has been reviewed.3 Its maximal excretory rate in man is about 36 mg/min/1.73 sq m; 50% to 60% is extracted by the kidney in one circulation, and clearance averages 400 ml/min.4 Glomerular filtration is small compared with the amount secreted by active tubular transport. Ordinarily about 2% to 3% is excreted into the bile and limited intestinal absorption occurs.5 Binding to albumin in vivo appears much less than the 80% suggested by studies in vitro, and some PSP appears to enter cells other than kidney, liver, and intestine.
Gault MH, Koch B, Dossetor JB. Phenolsulfonphthalein (PSP) in Assessment of Renal Function. JAMA. 1967;200(10):871–873. doi:10.1001/jama.1967.03120230123018
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