Lithium is almost completely reabsorbed in the proximal tubule in parallel with sodium and water. What is not reabsorbed here is assumed to be fully excreted in urine, giving a reasonably accurate measurement of sodium reabsorption in the proximal tubule. Endogenous lithium clearance will be measured by inductively coupled plasma mass spectrometry (ICP-MS). The Gomez equations will be applied to calculate efferent arteriolar resistance, afferent arteriolar resistance, glomerular hydrostatic pressure, glomerular filtration pressure, and glomerular oncotic pressure. N-acetyl-β-D glucosaminidase (NAG) and NGAL, markers of tubular injury, will be measured by a spectrophotometric method using a commercially available kit. Routine blood and urine analyses will be performed at the Diagnostic Clinic Laboratory, University Hospital of North Norway, Tromsø.
Renal lithium clearance is hypothesized to be a useful indicator of renal tubular function.~In this study lithium clearance will be monitored in patients with sepsis associated acute kidney injury and in healthy controls.