A modified in vivo flow variation technique of microdialysis for sampling uremic toxins in the subcutaneous interstitial compartment.

BACKGROUND Uremic toxins are typically measured in plasma and little is known of their interstitial concentrations. We undertook experiments to validate a microdialysis technique for simultaneous recovery of small and large uremic toxins in the subcutaneous interstitial fluid (ISF). METHODS Microdialysis catheters were inserted into the subcutaneous interstitium of 8 subjects (controls and uremic patients) and perfused using two different solutions at incremental flow rates to determine analyte recovery and ISF concentrations of urea and protein. RESULTS 10% dextran-40 perfusate allowed the determination of interstitial concentrations of urea and protein reliably, by virtue of the exponential decay of their concentrations in the microdialysate with incremental flow rates (R(2) = 0.63-0.99). Interstitial and plasma urea correlated well (r = 0.95), as did interstitial urea from distant anatomical sites (r = 0.96). CONCLUSION Cutaneous microdialysis with dextran-40 allows measurement of small and large molecule concentrations in ISF, creating an opportunity to characterize ISF in uremia.