Tubulointerstitial nephritis: causes and treatment

Each kidney contains about a million tiny filters. Their tubes, called tubules, and the tissue packed between them, called the interstitium, concentrate urine and rebalance salts. In tubulointerstitial nephritis this tissue becomes inflamed and swollen. The term is often shortened to interstitial nephritis.

The American Kidney Fund says the inflammation lowers the kidneys' ability to clean the blood and make urine, and that it comes in two kinds. Acute interstitial nephritis comes on over a short time and is the most common. Chronic interstitial nephritis lasts longer, from weeks to years.

The inflammation is not a urinary infection, although some infections can trigger it. It is an immune-driven reaction inside the kidney tissue. Without treatment, the AKF says interstitial nephritis can cause kidney damage or kidney failure.

The American Kidney Fund says the most common symptom is passing less urine than usual. Others can include blood in the urine, fever, a rash, tiredness or confusion, nausea and vomiting, swelling in the hands, feet or elsewhere, weight gain and high blood pressure.

Many people have few or no symptoms, and the problem is found on a blood test. The NHS says many people with acute kidney injury do not get symptoms, especially if it is mild. When symptoms occur, the NHS lists passing a lot less urine than usual, feeling very thirsty, nausea or vomiting, swollen feet or legs, tiredness, dizziness, confusion or sleepiness, and breathlessness, especially when lying down.

The NHS advises asking for an urgent GP appointment or contacting NHS 111 if you think you may have acute kidney injury.

Acute interstitial nephritis is usually caused by an allergic or other reaction to a medicine. The AKF says more than 100 different medicines might cause it, and the types most likely to are antibiotics such as penicillin, over-the-counter anti-inflammatory painkillers (NSAIDs) and proton pump inhibitors, which treat excess stomach acid.

A Danish trial protocol divides acute cases by trigger: drug-induced about 75%, infection 5 to 10% and autoimmune disease 15 to 20%. It says inflammation can progress to scarring if the trigger is not removed.

Chronic interstitial nephritis is usually caused by another health problem. The AKF lists autoimmune diseases such as lupus, low blood potassium, high blood calcium, sarcoidosis and some infections. Never stop a prescribed medicine on your own because of something you have read. Ask a doctor or pharmacist.

A doctor will ask about every medicine you take, including how often and how long, and will include over-the-counter products and supplements, because these can be the clue. The AKF says they will also examine you, listen to the heart and lungs, check blood pressure and weigh you.

Blood tests and urine tests are the main checks. The NHS explains that acute kidney injury is diagnosed with a blood test for creatinine, a waste product removed by the kidneys, and that a higher level than usual means the kidneys are not working as well as they should. Scans such as ultrasound may be used to look for other causes.

A kidney biopsy, where a small piece of tissue is examined under a microscope, can confirm interstitial nephritis. The AKF says it may show granulomas, which can help doctors work out the cause. A research paper describes the inflammation as sitting around the tubules while the filters and vessels are typically spared.

The first and most important step in acute disease is to stop or change the medicine responsible. The AKF says this often restores kidney function quickly and the symptoms go away. If the kidneys have lost a great deal of function, a short period of dialysis may be needed until they recover.

Steroids are sometimes used. The Danish PRAISE trial protocol says there are no generally accepted guidelines for treating acute interstitial nephritis because of the lack of randomised trials, and that despite limited evidence, prednisolone is frequently used. It notes that retrospective studies have given mixed results, including a Scottish study that did not show an effect on kidney function at 12 months.

In chronic disease, doctors treat the underlying problem. The AKF says they may also prescribe medicines to control blood pressure and lower inflammation, and may advise lowering salt and protein intake. Kidney failure from interstitial nephritis may need dialysis or a transplant.

Recovery depends on how early the cause is found. The AKF says acute interstitial nephritis can cause permanent kidney damage if it is not found early enough. The Danish protocol says some patients recover kidney function completely, but as many as 30 to 70% do not fully regain it, leading to chronic kidney disease, and it quotes a 5 to 7% risk of needing long-term dialysis in biopsy-proven cases.

The NHS notes that many people with acute kidney injury recover fully within a few weeks, though more serious cases take several months, and some are left with permanent damage. After recovery you will have regular blood tests and check-ups to make sure the kidneys are working as expected.

The AKF advises talking to your doctor about the medicines you take and your risk of interstitial nephritis. Once a medicine has been identified as the cause, doctors usually record it as an allergy or reaction in your notes, so it is avoided in future.

The NHS suggests staying hydrated, speaking to a doctor before taking new medicines or supplements, and knowing the symptoms of acute kidney injury and when to seek help. This is especially important if you are aged 65 or older, have had AKI before, or have recently had surgery.

Interstitial nephritis is usually picked up through GP or hospital blood tests. The NHS says that if AKI is severe or the cause is unclear, you may be referred to a kidney specialist or admitted to hospital.

A private nephrologist can offer faster review and kidney biopsy where needed. Ask which medicine is suspected, whether a biopsy is advised, how kidney function will be followed, and which drugs should be avoided in future.