A NOBILE¹, HR SCHMID¹, E GRÜTER², R KUBIK³, JH BEER<sup>2

1</sup>Central Laboratory Cantonal Hospital 5404 Baden Switzerland, ²Department of Internal Medicine Cantonal Hospital 5404 Baden Switzerland, ³Department of Radiology Cantonal Hospital 5404 Baden Switzerland

Introduction. Several studies addressed the value of NGAL as a renal lesion marker in plasma and/or urine (« renal troponin »). So far, an acute kidney impairment is diagnosed by an increase of creatinine (i.e. decrease of eGFR) and/or a decrease of urine volume (RIFLE, AKIN).
Aim. To investigate the value of NGAL, we designed a retrospective in-house trial with patients planned for CT or MRI procedure. In collaboration with the departement of radiology, we intended to measure NGAL in comparison to usual creatinine (CREA) in plasma of patients receiving radiocontrast agents (CA), a treatment of known risk for renal impairment. During 08-2014 to 12-2014, plasma samples were frozen if patient was on the list for MRI or CT.
Method. NGAL was measured in those cases where at least one sample before and one after radiological intervention could be collected. Patients were assigned to 4 groups : A = CT with iodinated CA, B = CT without iodinated CA, C = MRI with non-iodinated CA and D = MRI without non-iodinated CA. NGAL quantitation was performed on a cobas6000 analyzer (NGAL, bioporto, DK). We assumed that CA exposure would lead to higher peaks of NGAL and/or CREA, mainly in group A or C. To compare the methods/groups at a most sensitive approach, we calculated for each patient the ratio of the highest NGAL value to the lowest NGAL value (NGAL-max/NGAL-min) within the series of samples. Same was done for CREA (CREA-max/CREA-min). The combination of the two ratios was declared as Q = (NGAL-max/NGAL-min)/(CREA-max/CREA-min). Q will be >1 if NGAL peaks proportionaly higher than CREA. Inversely, Q will be <1.
Results. The following Q ratios (median & range) were calculated: group A (CT/+CA, n=22) Q(A)=1.201 (0.814-2.584); group B (CT/-CA, n=34) Q(B)=1.077 (0.423-2.35); group C (MRI/+CA, n=23) Q(C)=0.975 (0.575-1.577); group D (MRI/-CA, n=7) Q(D)=1.012 (0.709-1.222).
Conclusion. A slight tendency vs higher Q values can be noted when CA were used, showing that NGAL peaks slightly higher than Creatinine. Overall, in our investigation and approach we did not see a significant over-increase of plasma NGAL compared to creatinine in these patient groups regarding CA use.