Creatinine proximal tubule reabsorption

The glomerular filtrate containing virtually very little protein (approximately 30 mg/dl) enters the proximal tubule. Approximately 80% of the water and solute from the glomerular filtrate is reabsorbed in the proximal tubule as an isotonic solution. Solutes such as glucose and proteins are almost totally reabsorbed. Creatinine, in contrast, is not reabsorbed. Approximately 65% of the sodium in the glomerular filtrate is reabsorbed in the proximal tubule by active transport. The rate of reabsorption of sodium in the proximal tubule, however, is under the... 

These plasma tests are used as indirect measurements of the glomerular filtration rate (GFR) to some extent, these endogenous tests supplement each other despite having different limitations. Plasma creatinine, urea, and cystatin C are normally filtered from the plasma, and they are reabsorbed or secreted by the proximal tubules to a minor extent, which differs between species. Tubular secretion leads to overestimation of GFR and it is higher in laboratory animals than in man. These secretions/reabsorption mechanisms may change as a consequence of major tubular injury. In addition to renal injury, the GFR may be altered by changes of renal hemodynamics or extracellular dehydration. 

Drug-Drug Interaction Lithium. Telmisartan 40 mg per day was added into the antihypertensive regimen of a 52-year-old schizophrenic woman who had been on lithium 900 mg and haloperidol 20 mg per day. Her lithium level increased to 2.6 meq/L from a range of between 0.83 meq/L and 1.02 meq/L prior to the introduction of telmisartan urea and creatinine increased from normal baseline values to 76 mg/dL and 4.6 mg/dL, respectively, and potassium level was 7.0 mmol/L. Following haemodialysis, her laboratory results retiuned to normal, symptoms abated and lithium was replaced with valproic acid [18 ]. The exact mechanism of this interaction is not known however, it is thought that activation of ATI results in increasing sodium reabsorption at the proximal convoluted tubules which subsequently results in reduction in aldosterone secretion. This ultimately causes hyperkalemia and hyponatraemia. Sodium depletion may cause increase in lithium reabsorption from the proximal convoluted tubules. 

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