Background: Isotope assessment of glomerular filtration rate (GFR) is frequently performed in patients with central venous catheters (CVCs). Use of the CVCs for administration of tracer and subsequent blood sampling would be less distressing for patients (particularly paediatric) and would reduce the frequency of failed samples due to poor venous access. However, the GFR test is quantitative and could be affected by incomplete tracer delivery due to adhesion to the CVC and also by contamination of blood samples due to adhered tracer leaching back into the sampled blood as it passes through the CVC.
Aim: This in vitro study aimed to quantify the effects on GFR assessment of tracer adhesion and leaching, in single-lumen and dual-lumen CVCs.
Method: New and clinically used single-lumen CVCs were injected with tracer (99mTc-DTPA and 51Cr-EDTA) and then flushed repeatedly with saline. The outflows were assayed in a gamma counter and, where possible, the CVCs were imaged on a gamma camera to take snap shots of tracer movement throughout a GFR assessment. In a separate experiment, a phantom patient was used to compare blood sampling through a dual lumen CVC with peripheral sampling.
Result and conclusion: A CVC successfully delivers >99% of tracer. Subsequent blood samples can be taken through the other lumen of a dual-lumen CVC but not through a single-lumen as this significantly alters the GFR result due to contamination.