# AKI Biomarkers: Risk, Stress, Injury, and Function

Ask what the assay predicts, in whom, and what action a positive result will change.

![Infographic: AKI Biomarkers: Risk, Stress, Injury, and Function](https://urinenephrology.org/visual-reference/images/student-aki-biomarkers.png?v=20261003c)

## Function, stress, and injury differ

Creatinine and urine output measure functional AKI. Cystatin C is another filtration marker. Urinary TIMP-2·IGFBP7 reflects tubular stress; NGAL and KIM-1 reflect injury-related biology, with assay- and setting-specific limitations.

## A defined use: TIMP-2·IGFBP7

Original FDA-cleared NephroCheck use: ICU patients age ≥21 with acute cardiovascular or respiratory compromise now or within the prior 24 hours. It supports clinical assessment of moderate/severe AKI risk over the next 12 hours; it is not a stand-alone diagnosis or outpatient screen.

## Interpret the reported result

For that assay, an AKIRisk score >0.3 is a risk signal, not a diagnosis of AKI or a dialysis indication. Use the assay’s actual units, intended population, and validated cutoff rather than borrowing another biomarker’s threshold.

## A positive result needs a care pathway

Reassess perfusion and congestion; review avoidable nephrotoxins and contrast exposure; review drug doses; track urine output and creatinine. These are targeted protective actions, not instructions to give fluid to every positive patient.

## Check reasons for misleading results

Sepsis/inflammation and extrarenal production affect some markers; CKD and timing also alter interpretation. A negative injury marker does not exclude obstruction or a hemodynamic fall in filtration.

## Separate established criteria from drafts

Use published creatinine/urine-output criteria for routine AKI staging. Label proposed KDIGO 2026 AKI/AKD biomarker concepts as public-review draft. Improved prediction alone does not establish improved patient outcomes.

## Supporting evidence

- [FDA NephroCheck review and intended use](https://www.accessdata.fda.gov/cdrh_docs/reviews/den130031.pdf)
- [Supporting guideline or source](https://kdigo.org/guidelines/acute-kidney-injury/)

## Source lessons

- [aki biomarkers student handout](https://urinenephrology.org/student-resources/aki/aki-biomarkers-student-handout.html)

Read alongside the full lessons; the findings and decisions shown here require the stated clinical context.