Acute kidney injury (AKI) is a sudden decline in kidney function that develops over hours to days, which can disrupt fluid, electrolyte, and acid-base balance.
It is important to distinguish AKI from CKD, as AKI develops rapidly and is often reversible, whereas CKD is a long-term condition that persists for more than 3 months. The table below summarises the key differences between CKD and AKI.
| CKD | AKI | |
|---|---|---|
| Onset | Gradual (>3 months) | Sudden (days) |
| Reversibility | Usually progressive, not reversible | Often reversible |
| eGFR Trend | Stable or slowly declining (typically) | Rapid decline |
| Urine Output | Often normal until advanced | May be acutely reduced |
Suspect AKI over CKD if an initial eGFR is lower than expected for the patient’s history or presentation. Don’t assume CKD or AKI from a single low reading. AKI is common in acutely unwell patients, e.g. with dehydration, hypotension, sepsis, or intercurrent illness. Follow-up eGFR is essential to determine whether it was AKI, CKD, or AKI on CKD.
AKI and CKD are closely linked: AKI can lead to CKD, and CKD increases the risk of AKI.
Patients recovering from AKI should have their CKD medications reviewed. RAS inhibitors (ACE inhibitors or ARBs) and SGLT2 inhibitors are often temporarily withheld during acute illness but should usually be restarted once the patient has recovered, unless a new contraindication has arisen. These treatments are NOT nephrotoxic and provide important kidney and cardiovascular protection.
| AKI stage | Creatinine | Urine output |
|---|---|---|
| 1 | Serum creatinine 1.5–1.9 × baseline or ≥26 μmol/L (≥0.3 mg/dL) | <0.5 mL/kg/hour for 6–12 hours |
| 2 | Creatinine 2.0–2.9 × baseline | <0.5 mL/kg/hour for ≥12 hours |
| 3 | Creatinine ≥3.0 × baseline or ≥354 μmol/L (≥4.0 mg/dL) or initiation of kidney replacement therapy | <0.3 mL/kg/hour for ≥24 hours or anuria for ≥12 hours |
Why was the blood test taken?
Creatinine rise within stable clinical context may reflect unstable CKD instead of AKI, especially if longer time period between current and baseline creatinine.
* UK Kidney Association Clinical Practice Guidelines (2023) recommend emergency assessment and treatment of severe hyperkalaemia (K+≥6.5mmol/l)