Theoretically an excellent fractional phenolsulfonphthalein (PSP) clearance implies an excellent urea or creatinine clearance, while a poor PSP clearance can coexist with other clearances ranging from excellent to poor. This prediction was strikingly verified in a study in which results of a 15-minute PSP test, simple enough to be done in the physician's office, were compared with the results of other clinical methods for measuring glomerular filtration. Observations on 350 patients showed that this test not only indicates tubular function but also indicates the lowest glomerular function compatible with that level of tubular function. This is an advantage in assessing the renal status of patients anticipating surgery.
Lapides J, Bobbitt JM. PREOPERATIVE ESTIMATION OF RENAL FUNCTION. JAMA. 1958;166(8):866-869. doi:10.1001/jama.1958.02990080010002