Which of the following is NOT listed as an early or late biomarker of AKI?

• A. Neutrophil gelatinase-associated lipocalin
• B. Liver-type fatty acid-binding protein
• C. Kidney injury molecule-1
• D. Creatinine

Answer: (D)

The key idea here is distinguishing between markers that signal actual kidney injury and markers that reflect kidney function. In AKI, several biomarkers rise as a result of tubular injury: NGAL appears quickly after nephron injury, KIM-1 is upregulated on injured proximal tubule cells and sheds into urine, and L-FABP is released in response to proximal tubule damage. These are considered early or later indicators of injury itself.

Creatinine, on the other hand, is a functional marker. It tracks glomerular filtration rate rather than directly signaling tubular injury. Its rise depends on reduced filtration and can lag behind actual injury, influenced by muscle mass and urine output. Because it reflects function rather than injury signal, creatinine is not listed as an early or late biomarker of AKI in the same way as NGAL, KIM-1, or L-FABP.

So the correct choice is the one representing creatinine, since it’s not an injury biomarker observed in the early or late phases of AKI.