Clinical Evaluation of Proximal Tubule Na/Fluid Reabsorption:Lithium Clearance vs “Volume or Chloride Factors” During Maximal Water Diuresis and Furosemide Administration
The clinical method for evaluating proximal tubule Na and fluid reabsorption (NaPR) consists mainly on clearance studies during maximal water diuresis; in this setting, being ADH suppressed, CH20 may be used as an index of NaCl reabsorption in the dilui ting segments of the nephron; as a consequence CH20 added to Cl excretion (CH20+CCL/GFR)(chloride factor) may reasonably represent distal delivery. An alternative method is to evaluate maximal urinary flux (V/GFR)(“volume factor”)(1). This theoretical background is incompletly correct as a consistent, ADH independent, water back diffusion, occurs secondary to the tubule-interstitium osmotic gradient (2); this osmotic gradient can be reduced, although not abolished, by furosemide administration (f); in this condition “volume factor” may be a more accurate index of the delivery of fluid out of the proximal tubule (2). Recently (3), Li clearance has been proposed as the most specific method for evaluating NaPR.
KeywordsPhosphorus Lithium Creatinine Furosemide Estima
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