Pre-renal acute kidney injury: causes, symptoms and recovery

Acute kidney injury (AKI) is when something suddenly causes your kidneys to stop working as well as they should, according to the NHS. Kidney Care UK describes it as a sudden drop in kidney function that can range from a small loss of function to complete failure, and stresses that it normally happens as a complication of another condition.

Doctors group the causes into three types, as NICE CKS sets out. Pre-renal causes are those due to reduced blood flow to the kidneys and/or low blood pressure. Intrinsic renal causes involve structural damage to the kidney itself. Post-renal causes are due to a sudden blockage of the urinary tract. In pre-renal AKI the kidneys are initially structurally healthy; they are struggling because of what is happening elsewhere in the body.

That is why this type is often the most reversible. If the blood supply to the kidneys is restored quickly, function often returns. If the problem continues, the kidneys can be damaged directly, and a pre-renal problem may turn into an intrinsic one.

The NHS lists dehydration, low blood pressure and blood loss, and infections or sepsis, among the possible causes of AKI. Kidney Care UK lists illness or infection, a reaction to medication, low blood pressure, dehydration and kidney stones. NICE CKS lists sepsis, hypovolaemia (low blood volume), hypotension, dehydration and reduced fluid intake among the factors that raise risk, and suggests suspecting AKI in a person with an acute illness such as diarrhoea and vomiting.

Medicines can play a part. The NHS lists long-term use of some medicines, such as ACE inhibitors, anti-inflammatory medicines (NSAIDs) and medicines that make you pee more (diuretics), and the dye (contrast) injected for some scans. These are not harmful for everyone, but they can add to the strain on the kidneys when you are unwell or dehydrated.

• Being aged 65 or older.

• Having had AKI before.

• Recent surgery.

• Long-term kidney, heart or liver conditions, or diabetes.

• Relying on others for fluid intake, as NICE CKS notes.

• Taking illegal drugs.

The NHS says many people do not get symptoms, especially if AKI is mild. Where there are symptoms, it lists peeing a lot less than usual, feeling very thirsty, feeling or being sick, swollen feet or legs, feeling tired, dizzy, confused or sleepy, and feeling breathless, especially when lying down. Kidney Care UK says the symptoms can appear suddenly over just a few days and describes a feeling of being generally ill, like a hangover.

Because symptoms can be subtle, AKI is often found when a person has blood tests for another reason or is in hospital. The NHS says it is often diagnosed that way.

The NHS says AKI is diagnosed using a blood test that measures creatinine. Higher levels than usual mean the kidneys are not working as well as they should. A doctor may also ask for a urine sample, ask how often you have been peeing, and check your pulse and blood pressure. Depending on the suspected cause, an ECG or scans such as an X-ray, CT scan or ultrasound may be arranged.

NICE CKS says the diagnosis and its staging is based on acute changes in blood creatinine and/or a reduction in urine output. Assessing how much fluid the person has, and looking for a blockage, are part of working out whether the problem is pre-renal.

If AKI is severe or the cause is unclear, the NHS says you may be referred to a kidney specialist (nephrologist) or admitted to hospital.

The NHS says treatment depends on how bad the AKI is and what is causing it, and may need to be in hospital. Kidney Care UK says that if dehydration is the cause it may get better by simply drinking more water, and that someone who is very dehydrated may be given fluids through a drip.

Other measures the NHS lists include treating an infection, medicine to raise blood pressure, and stopping or changing any medicine that could be damaging the kidneys. Kidney Care UK explains that your doctor may advise you to temporarily stop some medicines or adjust the dose, known as sick day rules, and will review them once kidney function recovers. Never stop prescribed medicine on your own without advice.

Dialysis is only needed in severe cases and is usually for a few days or weeks until the kidneys recover, according to the NHS.

The NHS says AKI is a serious condition and can be life-threatening if not treated, but many people recover fully within a few weeks with no long-term effects. If it is more serious it can take several months. Some people end up with permanent damage and chronic kidney disease, and this is more likely if the AKI was severe or you already have other long-term health problems.

Kidney Care UK says your GP will monitor your kidney function and blood pressure for at least three years after an episode of AKI. Checking with a doctor before starting any new medicine or herbal supplement is sensible in case it could harm the kidneys.

The NHS advises staying hydrated so that your pee is pale and regular through the day, especially in hot weather or if you are being sick or have diarrhoea, speaking to a doctor before taking new medicines or supplements, and knowing the symptoms of AKI and when to get help. If you are at higher risk, ask your GP or pharmacist which of your medicines may need to be paused during a stomach bug or other illness.