Acute kidney injury

Acute kidney injury is a sharp drop in kidney function over hours or days. The blood stops being cleaned properly, and water, salts and waste products build up in the body. The name is misleading: it has nothing to do with a blow or a wound. Almost always it is a complication of another illness — a severe infection, dehydration, a heart problem, a flare of a long-term condition. The good news is that when the cause is dealt with in time, the kidneys usually recover completely.

Why this is not the same as chronic kidney disease

Chronic kidney disease drags on for years, creeps up unnoticed and cannot be wound back. Acute injury is an event with a clear beginning: someone fell ill with something, and the kidneys could not take the strain. The two are not sealed off from each other: having been through an acute episode raises the risk of chronic disease later, and kidneys that are already damaged fail acutely more easily.

The kidneys filter the entire volume of blood many times a day. They are the first to suffer when blood pressure falls, fluid is lost, or a substance appears in the blood that they have to clear. That is why acute kidney injury is a common finding in people admitted to hospital for something else entirely.

What the person notices

The treacherous part is that at the start there may be no sensation at all — it is picked up on a blood test. When signs do appear, they are usually these:

• noticeably less urine, and fewer trips to the toilet;
• swelling of the ankles, feet and lower legs, and of the face in the morning;
• nausea, vomiting, loss of appetite, a metallic taste in the mouth;
• weakness, drowsiness, trouble concentrating;
• breathlessness and discomfort when lying flat;
• itchy skin and cramps in the calves.

One point is worth stating separately: urine may still come in normal amounts. Passing water normally does not rule the diagnosis out.

Signs that mean calling for emergency help

Do not delay the call if an unwell person develops any of the following:

• no urine at all for half a day;
• severe breathlessness, inability to lie down, bubbling breathing — fluid is collecting in the lungs;
• sudden muscle weakness, an irregular heartbeat, a sense of the heart missing beats — this is how excess potassium in the blood shows itself, and it can stop the heart;
• confusion, unusual drowsiness, seizures;
• urine the colour of strong tea or cola after heavy exertion, after hours lying immobile, or after a seizure — this can be breakdown of muscle tissue, which clogs the kidney from within;
• in a child, bloody diarrhoea followed days later by pallor, listlessness and little urine — a rare but dangerous condition in which red blood cells are destroyed and the kidneys are hit.

What usually sets it off

The causes sort neatly by where the failure sits: before the kidney, in the kidney itself, and after it.

• Before the kidney — not enough blood reaches it: heavy vomiting and diarrhoea, bleeding, burns, severe infection with falling blood pressure, a weakly pumping heart, advanced liver disease.
• In the kidney itself — its tissue is damaged: inflammation of the kidney filters, inflammation of the vessels, an allergic reaction to a drug, muscle breakdown and, less often, poisoning.
• After the kidney — the urine has nowhere to drain: an enlarged prostate, a stone blocking the outflow, a tumour in the pelvis, compression of the ureters.

Contrast dye used in CT scanning also plays a part: with healthy kidneys the risk is small, and where they are already diseased it is taken into account beforehand.

Who pays a higher price for falling ill, and what to do about medicines

The risk is greater over the age of sixty-five, in anyone who already has kidney disease, diabetes, heart failure or cirrhosis, and after major surgery.

Everyday medicines deserve a separate mention. Harmless in ordinary life, they hit the kidneys hard against a background of vomiting, diarrhoea or high fever. These are the non-steroidal anti-inflammatory painkillers, some blood pressure drugs, diuretics and certain antibiotics. If you take any of them regularly and suddenly go down with a stomach bug or cannot keep fluids in, contact your doctor: some of them are paused for the duration of the illness. Never stop blood pressure or heart medicines on your own — that decision belongs to the doctor.

And one simple everyday rule: during an illness with fever, vomiting or diarrhoea you have to drink, and if drinking is not working, that in itself is a reason to seek help rather than wait.

How it is picked up and what helps

The basis of the diagnosis is a blood test for creatinine and urea, with potassium, sodium and the acid balance of the blood added. Urine output over twenty-four hours is measured. A urine test is examined: protein and red cells in it point to disease of the kidney tissue itself. An ultrasound scan shows whether anything is blocking the outflow and what the kidneys look like.

Treatment is aimed at the cause. Fluids are replaced if the person is dehydrated, infection is treated, drugs that harm the kidney are withdrawn, a catheter or drain is placed if the urine is blocked, and inflammation of the kidney tissue is worked through with a kidney specialist. When the kidneys cannot cope and potassium and fluid build up, dialysis is started — usually temporarily, until recovery.

Most people get better. Even so, the kidneys are worth watching after the episode: repeat blood and urine tests a few months later, keep an eye on blood pressure and check every new medicine with a doctor. The episode itself should be remembered and mentioned to doctors, because it changes how things are prescribed.

Online consultation when kidney damage is suspected

The acute illness is treated in person, often in hospital. But much of what surrounds it is easily handled remotely.

• assess your symptoms and say plainly whether emergency help is needed or tests will do;
• read your blood and urine results and explain what those numbers mean in your case;
• go through your list of long-term medicines if you are in a risk group;
• advise what to do about those medicines when you are ill and cannot keep fluids down;
• set up follow-up after discharge and establish whether the kidneys have recovered.

If what you describe sounds serious, the doctor will not sit on that conclusion and will tell you plainly to get to hospital.

This material is for information only and does not replace medical advice.