Renal tubule ammonia excretion maximal excretion test

PAH is not catabolized after injection, about 20% is filtered from the glomerulus in its original form, 80% is excreted by the proximal tubule, and is not reabsorbed by the renal tubule. Its excretion increases with the increase of plasma PAH level. When the plasma concentration increases to a certain limit (about 600mg / L), the renal tubular excretion has reached the maximum. Even if the plasma concentration of PAH is increased, the excretion in urine does not increase any more. At this time, the excretion is For the maximum excretion of ammonia uric acid. The maximum excretion minus the glomerular filtration excess (measured by inulin clearance), that is, TmPAH, can be used as an indicator of the number and quality of renal tubules, and is one of the methods for measuring the active secretory function of proximal tubules.