Measured GFR Implemented in a US Clinical Practice: Comparing 4-Hour and 10-Hour Plasma Iohexol Clearance

Background: It is well recognized that estimated glomerular filtration rate (eGFR) can be highly inaccurate in assessing measured GFR (mGFR) for individual patients. mGFR using non-radiolabeled plasma iohexol clearance is straightforward and easily implementable in clinical practice, but it is not widely available in the US. In 2019, we implemented mGFR by a 4-hour plasma iohexol clearance as part of clinical care at Houston Methodist Hospital. The mGFR is orderable via an Epic order set. Recent studies (White CA; PMID: 32750458) and European Kidney Function Consortium (EKFC; under review) guidelines emphasize the importance of a long plasma clearance interval (10-hours) if the GFR is expected to be low (<30 mL/min/1.73 m2). We have now updated our mGFR protocols to include both the standard (4-hour) and the long (10-hour) clearances. We present these case studies as an educational tool to enhance the understanding of mGFR and promote dissemination of mGFR protocols. Methods: We describe 3 patients that had simultaneous measurement of creatinine, cystatin C, and mGFR by 10 hour plasma iohexol clearance. We compared the 4-hour and 10-hour mGFRs with eGFRs. We defined eGFR to be accurate in assessing the mGFR if the eGFR was within ±5 ml/min/1.73 m2 of the 10-hour mGFR. Results: See Table 1. Conclusion: mGFR is the best available test of kidney function and it is not influenced by age, sex, or race. We have successfully implemented standard (4-hour) and long (10-hour) mGFR in routine practice at a busy clinical center in the US. Our cases provide important educational opportunities for nephrologists interested in learning and implementing mGFR in routine clinical care.