Table 2 |.

Characteristics of an ideal biomarker of acute tubular injury

Property	Explanation
Easily measured	Reliable quantification of a biomarker requires that the biomarker is stable during collection and processing and the test distinguishes the gene product from its metabolic product
‘Rapid on, rapid off’ kinetics	Biomarker expression must be upregulated shortly after the injurious stimulus and downregulated after termination of stimulus
Dose-dependent response	The quantity of the biomarker must be proportional to the number of injured nephrons or the severity of the injured nephrons. Hence, a biomarker must be sensitive to the injury of a small number of nephrons but also demonstrate a broad dynamic range to respond to widespread injury
Tubular origin	In acute renal failure caused by tubular injury, the biomarker must be expressed at sites of tubular damage
Specific	An ideal biomarker should be able to distinguish the injury induced by different types of acute renal failure, such as volume depletion versus tubular damage and potentially proximal tubular from distal tubular injury
Essential to homeostasis, injury or repair	An ideal biomarker should reflect the injury process, a property called ‘biological plausibility’, e.g. KIM1 is needed to remove cellular debris, whereas NGAL defends the urinary system from infection
Distinct from functional marker	Analysis with an ‘injury’ biomarker should interact in a synergistic fashion with analysis by a ‘functional’ biomarker

KIM1, kidney injury molecule 1; NGAL, neutrophil gelatinase- associated lipocalin.