Table 1.

Summary of biomarkers.

	Specimen	Biomarker Type	Intended Use	Recommended Cut-off	Limitations
Creatinine	Serum	Functional	Diagnosis of AKI and CKD	Per KDIGO criteria, >0.3 mg/dL increase in 48 h or >1.5x increase from baseline in 7 days	Affected by age, race, muscle mass, fluid status, medications.
					Rises 24–48 h after injury and only after >50% nephrons are lost/injured.
Cystatin C	Plasma (or serum)	Functional	Used for estimation of GFR and medication dose adjustments in pediatric and adult patients.	No universally accepted cut-offs for CKD, as used in eGFR estimating equations; in pediatric patients post-CPB, maximum sens/spec for 12-hr AKI prediction was 1.16 mg/L	Levels may be different in different age groups. Lower accuracy in hypermetabolic states such as malignancy, uncontrolled thyroid disease, with steroid use. Higher CRP, WBC, lower serum albumin associated with higher levels.
			Has been used for AKI prediction in small cohorts.
			In large adult cohorts can predict worse outcomes.
TIMP-2*IGFBP7	Urine	Stress	In conjunction with clinical evaluation, in ICU patients 21+ years with acute cardiovascular/respiratory compromise in the past 24 h, as an aid for risk assessment for moderate/severe AKI within 12hrs of assessment.	>0.3 for high sensitivity, acceptable specificity; not official, but >2.0 for high specificity according to research studies	Per package insert, should not be used as a standalone test.
					Interference with urine albumin >125 mg/dL, invalidation if > 3000 mg/dL, less accurate in patients with hyperbilirubinemia
NGAL	Urine	Damage	AKI prediction in high-risk patients. Future delineation of “subclinical AKI” or a cohort of patients with normal SCr but at risk of worse clinical outcomes.	No FDA-approved assay, levels will vary by lab. >150 ng/mL has high sensitivity. >580 ng/mL has high specificity in a large adult meta-analysis.	False elevations in sepsis, malignancy, COPD exacerbations, and especially with leukocyturia. Levels impacted by hyperbilirubinemia.