#5535 CALCIUM EXCRETION FRACTION AS AN EMERGING PARAMETER FOR AN ACCURATE DIFFERENTIAL DIAGNOSIS OF ACUTE KIDNEY INJURY

Abstract

Abstract Background and Aims Urinary parameter determination is an essential tool for differentiating acute kidney injury (AKI) etiology. The most used ion in clinical practice is sodium (and its excretion fraction, NaEF), followed by urea (UreaEF) (that is useful in certain circumstances such as diuretic treatment). However, tubular transport includes other anions and cations that have not been widely studied. In the present study, we aim to evaluate the relation between AKI etiology (i.e. functional vs acute tubular necrosis) and calcium excretion fraction (CaEF). Method This is a transversal study including consecutive patients with diagnosis of AKI. Patients with suspicion of non-functional or ATN etiology (such as those with proteinuria, hematuria) were excluded. At admission, we collected epidemiological data, comorbidities and active treatments. AKI etiology was determined based on urinary parameters (sodium, urea) and recovery pattern of kidney function after treatment instauration. We compared CaEF in patients with ATN and functional AKI in the whole sample and among patients with and without previous CKD and diuretic prescription. Results We included 94 AKI episodes (55% female, 76±15 years). Forty-five (48%) patients had chronic kidney disease (CKD) at baseline and 56 (60%) were receiving treatment with diuretics. Of the 94 AKI, 78 (83%) presented a functional etiology and 16 (17%) were catalogued as ATN. Median CaEF was 1.09 (0.63-2.58) %. CaEF was associated to the etiology of AKI. In patients with functional AKI, median of CaEF was 0.95 (0.60-1.84) % in contrast to ATN (2.33 [1.22-7.27] %)(p<0.001). CaEF presented a positive and significant correlation to NaEF (ρ 0.574, p<0.001) and UreaEF (ρ 0.409, p<0.001). An adjusted regression model including the presence of CKD at baseline and diuretic treatment showed that CaEF independently predicted ATN (OR per 1% increase 1.42, 95%CI [1.16-1.75), p<0.001]. In patients without CKD, CaEF predicted ATN (OR 1.61, 95%CI [1.13-2.28], p = 0.008), in contrast to the cohort with CKD where only a trend was demonstrated (OR 1.29, 95%CI [0.99-1.69], p = 0.057) (Figure 1). CaEF also predicted ATN irrespective of the diuretic prescription at baseline (OR 1.35, 95%CI [1.05-1.74], p = 0.018 for diuretic users and OR 1.57, 95%CI [1.06-2.32], p = 0.025 for non-diuretic users) (Figure 1). Receiving operator curves (ROC) demonstrated a 0,712 area under the curve (AUC) of CaEF >1.6% for ATN, that was the best value for diagnosis in terms of sensitivity and specificity. CaEF>1,6% predicted ATN (OR 8.09, 95%CI [2.32-28.2], p = 0.001) after adjusting for the presence of CKD at baseline and diuretic treatment. Conclusion CaEF could help in the identification of the AKI etiology as higher values (i.e. >1.6%) are independently associated with ATN.