Diseases & care
Acute kidney injury: what it is, why it happens and how it is managed
Acute kidney injury (AKI) is a sudden fall in kidney function over hours or days. It is common in people who become acutely unwell, often silent in its early stages, and frequently preventable. Understanding it matters because simple actions — staying hydrated, reviewing certain medicines during illness — can stop it developing or worsening. This guide explains what AKI is and how it is managed.
Education and reference only. This article explains how treatments work in plain language — it contains no doses and is not a substitute for advice from your doctor or pharmacist. Always discuss your own treatment with a qualified clinician.
What the kidneys do and what AKI means
The kidneys filter waste and excess fluid from the blood, balance salts and water, and help control blood pressure. In acute kidney injury, this filtering function drops suddenly. It is detected by a rise in a blood marker called creatinine and/or a fall in urine output. AKI is graded in stages by severity. It is not a disease in itself but a sign that something is stressing the kidneys — and identifying that cause is the key to treating it.
The three types of cause
AKI causes are grouped by where the problem lies. "Pre-renal" causes reduce blood flow to the kidneys — dehydration, blood loss, severe infection (sepsis) or heart failure; this is the commonest group and often reversible if caught early. "Intrinsic" causes damage the kidney tissue itself — for example certain drugs, toxins or inflammation. "Post-renal" causes obstruct the flow of urine out of the kidneys — such as an enlarged prostate or kidney stones. Working out which type is present directs treatment, because the fixes are very different.
Why medicines and illness matter
A major, preventable contributor to AKI is the combination of an acute illness (with dehydration) and certain medicines. Drugs such as some blood-pressure medicines (ACE inhibitors and ARBs), diuretics ("water tablets") and anti-inflammatory painkillers (NSAIDs) can reduce the kidneys' ability to cope when someone is unwell and not drinking. This is why "sick day guidance" often advises temporarily pausing specific medicines during an acute illness with vomiting or diarrhoea, on medical advice. Contrast dye used in some scans can also stress vulnerable kidneys.
Treatment, recovery and prevention
Treatment targets the cause: fluids for dehydration, treating infection, relieving an obstruction, and stopping or adjusting the medicines that are contributing. Kidney function and fluid balance are monitored closely, and dangerous consequences — such as a high potassium level or fluid overload — are managed. Most AKI recovers if the cause is treated promptly, though severe cases may need temporary dialysis to support the kidneys while they recover. Prevention is powerful: staying hydrated during illness, sensible use of NSAIDs, and reviewing at-risk medicines when unwell all reduce the risk.
In short
Key takeaways
- Acute kidney injury is a sudden fall in kidney function, detected by a rising creatinine or falling urine output.
- Causes are grouped as pre-renal (reduced blood flow, the commonest), intrinsic (kidney damage) and post-renal (obstruction).
- Dehydration during illness combined with certain medicines (ACE inhibitors/ARBs, diuretics, NSAIDs) is a common, preventable cause.
- Treatment targets the cause; most AKI recovers if caught early, though severe cases may need temporary dialysis.
- Staying hydrated and reviewing at-risk medicines during acute illness are key preventive steps.
Answers
Frequently asked questions
Is acute kidney injury the same as chronic kidney disease?
No. AKI is a sudden, often reversible drop in kidney function over hours or days, whereas chronic kidney disease is a long-term, gradual reduction. However, AKI can worsen existing chronic kidney disease and repeated episodes can contribute to long-term damage.
Why might I be told to pause certain tablets when I am ill?
Some medicines (such as ACE inhibitors, ARBs, diuretics and anti-inflammatory painkillers) can reduce the kidneys’ ability to cope when you are dehydrated from vomiting or diarrhoea. "Sick day rules" may advise temporarily pausing them on medical advice to protect the kidneys.
Does AKI always need dialysis?
No. Most AKI is managed by treating the cause and supporting the kidneys, and recovers without dialysis. Dialysis is reserved for severe cases as a temporary support while the kidneys recover.
Go deeper
Related guides
Sources
Where this is drawn from
- NICE NG148 — Acute kidney injury: prevention, detection and management
- Think Kidneys — AKI and sick day guidance
- The Renal Association — AKI clinical practice guidelines
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