In this study, despite hyperhydration and forced diuresis with furosemide and mannitol, 10 out of 42 patients who underwent CIS-CT to treat urothelial carcinoma suffered AKI. Moreover, acute renal function deterioration was predicted by increased urinary L-FABP excretion within six hours after receiving CIS-CT and, in those with AKI, the increase in urinary L-FABP excretion preceded the rise in sCr by over 2 days. In contrast, no appreciable changes in urinary L-FABP levels were observed in patients with stable renal function throughout the whole observation period.
The weaknesses of using serum creatinine as a diagnostic marker for AKI include its relatively late elevation, its indirect relationship to kidney damage and its influence by extrarenal factors [15]. Differences in creatinine production related to age, sex, race, and weight, its secretion by the renal tubular epithelium, possible influence by some drugs, compromised metabolism of creatinine in AKI owing to hypercatabolism, and creatinine dilution in cases of volume overload are reasons why creatinine might not be a reliable marker for AKI. More sensitive and specific markers for acute renal injury are needed.
Recently identified urinary biomarkers for AKI include N-acetyl-D-glucosaminidase, α1-microglobulin, β2-microglobulin, NGAL, L-FABP, and KIM-1. NGAL [16] and Kim-1 [17] are reportedly useful for early detection of cisplatin-induced AKI. Although NGAL can be a useful marker for AKI [18, 19], urinary NGAL may be produced extrarenally in response to systemic stress; and urinary KIM-1 levels decrease significantly at lower and higher storage pH [20]. This means that some samples may have stability issues. Moreover, if urine cannot be immediately tested, accuracy may vary. In contrast, urinary L-FABP is not affected by urinary sediment and can therefore be measured in spot urine samples. Furthermore, urinary L-FABP measurements are highly reproducible [21]. Finally, rather than fluctuating with exercise [22], urinary L-FABP concentration is extremely stable. All these reasons indicate that urinary L-FABP may be a more stable and reproducible marker for evaluating early renal dysfunction.
In this study, more women were in the AKI+ group than in the AKI− group. Risk factors for AKI included age >65 years, female sex and metabolic complications in one report [23], and age > 70 years, diabetes mellitus, chronic kidney disease, heart disease, gout, infections, surgery and some drugs (NSAIDs, diuretics, aminoglycosides and vancomycin) in another report [24]. Other than sex, background factors, such as age, renal function and complications, did not significantly differ between the AKI+ and AKI− groups in this study. Patients with upper tract urothelial carcinoma are often elderly (i.e., over 65 years of age) and often have only a single kidney owing to nephroureterectomy, so they are at higher risk of developing AKI. Therefore, early diagnosis of AKI is important for patients with upper tract urothelial carcinoma. As urinary L-FABP may help diagnose AKI within 6 hours after cisplatin administration, it is a useful marker.
This study had some limitations. First, it was a single-centre, cross-sectional study with a small sample population. Second, the study group included only Japanese patients, which may limit generalizability of its results to other groups. Third, the eGFR averaged over 60 in this study. Different results may be obtained in patients with lower renal function.
In conclusion, early increase in urinary L-FABP may help identify patients at risk of cisplatin-induced AKI, who might benefit from treatments to prevent nephrotoxicity.