HONG KONG—Estimated glomerular filtration rate (eGFR) may be an inaccurate measure of kidney function at discharge among patients hospitalized for acute kidney injury (AKI), a new study suggests.

A British team found that eGFR overestimates renal function by 1.23-fold in patients being discharged after an episode of AKI. They believe the overestimation is due to the calculations for eGFR not taking into account the significant loss of muscle mass in critically ill patients.

“When a patient who had AKI leaves hospital with the same creatinine levels they entered hospital with, we might be falsely reassured they had complete recovery of renal function,” lead investigator John Prowle, MD, MSc, of the Royal London Hospital in the U.K. told Renal & Urology News. `However, when you factor in the expected fall in creatinine due to loss of muscle mass, we can see that some patients in fact had developed or progressed to CKD [chronic kidney disease] after their AKI and critical illness.”

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Dr. Prowle and his co-investigators presented the results in poster form at the 2013 World Congress of Nephrology. They analyzed information from a database of all patients who were admitted to the Royal London Hospital’s intensive care unit (ICU) for five or more days in 2011 and survived to discharge. They excluded anyone who had a current or new diagnosis of end stage renal disease or who had received a kidney transplant.

For baseline creatinine level, researchers used the last available result from between one year and seven days before hospital admission or, if neither of these was available, they used creatinine level at hospital admission.

The 282 patients in their study had a median age of 51 years and 68% were male. Of them, 180 had AKI in the ICU, and 56 received dialysis. The median discharge creatinine level was 57 µmol/L (range 16-654 µmol/L).

The median creatinine level of patients without AKI decreased from 84 µmol/L at admission to 54 µmol/L at discharge. Their discharge eGFRs were significantly higher than the predicted normal eGFR for patients of the same age (median 115 vs. 95 mL/min/1.73 m2). Among patients without AKI, this was 110 vs. 98 mL/min/1.73 m2.

The investigators calculated that 44% more patients (36 vs. 25) should have been diagnosed with CKD at discharge, including three more patients who should have been diagnosed with CKD stage 3a, four more with stage 3b, and four more with stage 4.

“The message is that clinicians should be careful in judging renal recovery on the basis of hospital-discharge creatinine or an eGFR calculated from it,” Dr. Prowle said.