These include specific gravity, osmolality, urine excretion of electrolytes, the free water clearance test, and certain substances secreted by renal tubules. Phenolsulfonphthalein (PSP) excretion Phenolsulfonphthalein is excreted mainly by the renal tubules. In general, results give about the same clinical information as the creatinine clearance rate since glomerular and tubular dysfunction usually occur together in […]