Final answer:
Creatinine (Option A) is the latest biomarker to indicate acute kidney injury, as it typically rises within hours to days after kidney injury, compared to other biomarkers that may respond more rapidly.
Step-by-step explanation:
The question asks which biomarker is the latest indicator of an acute renal injury in a 75-year-old man who is oliguric following an open abdominal aortic aneurysm (AAA) repair. Among the listed options, the latest indicator of acute kidney injury (AKI) would be creatinine (Option A). This is because other biomarkers like Cystatin C (B), Neutrophil Gelatinase-Associated Lipocalin (NGAL) (C), Interleukin-18 (IL-18) (D), and Kidney Injury Molecule-1 (KIM-1) (E) can increase more rapidly than creatinine in response to kidney injury. Creatinine levels typically rise within several hours to days after the actual loss of kidney function has occurred. Therefore, an increase in serum creatinine is not an immediate response but a later occurring biomarker following renal injury.
It is important to note that a kidney biopsy may be performed in cases of AKI to provide a definitive diagnosis, unless the cause is apparent and screening investigations are reassuringly negative. Factors affecting renal function such as medication interference with normal bladder emptying, benign prostatic hypertrophy, kidney stones, and obstructed urinary catheter must be considered. Furthermore, previous measurements of renal function can provide a comparison especially in patients known to have chronic renal failure.