eJournal Club - Albuminuria and AKI

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This month’s eJournal club concerns biomarkers of AKI. Therehas been considerable interest in developing novel biomarkers of AKI and CKDand a lot of effort has been focused on novel biomarkers such as NGAL, KIM-1and IL-18. The TRIBE-AKI consortium has published a number of well-designedstudies investigating novel and traditional biomarkers. The reason that thesebiomarkers are desired is because creatinine elevations tend to occurrelatively late in the course of AKI and therefore, the sense is that this istoo late to initiate therapies which may prevent progression of AKI. However,the results of these biomarker studies have been relatively disappointing andthey have not yet entered regular clinical practice.
This month in CJASN, a study was published looking atthe performance of post-operative albuminuria as a biomarker of AKI in patientsfollowing cardiac surgery. The highest quintile of albuminuria was associatedwith a RR of 2.97 for AKI relative to the lowest quintile. While this appearsgood and the AUC for a model including albuminuria to predict AKI was 0.81, themajority of patients with albuminuria did not develop AKI and the model misseda significant number of patients with AKI. Still, when you combine this withother studies showing that the urinalysis is an excellent predictor of outcomein patients with AKI, older biomarkers are not looking so bad after all.Perhaps we will be able to come up with a combination of biomarkers which willallow us to better predict those patients at greater risk of AKI. To me, itseems that the bigger issue is low sensitivity rather than low specificity. Iwould rather have a model which will allow me to rapidly rule out those whowill not develop AKI than one that will misclassify patients into a low riskgroup.
It was interesting in this study that ACR was not a goodpredictor of AKI – the absolute level of albumin performed better. This is at oddswith the majority of studies which suggest that albumin should be corrected forcreatinine level. This is possibly due to the large variation in creatininegeneration in patients in the ICU – although relatively constant under normalcircumstances, the amount of creatinine produced daily changes rapidly in sickpatients – as was evidenced by a recent study of creatinine excretion inpatients on CRRT.