Hydronephrosis

Also called Swollen kidney, Obstructed kidney

Urine backing up and swelling the kidney. An obstructed, infected kidney is an emergency needing drainage, not just antibiotics.

What it is

Swelling of a kidney because urine cannot drain away.

The cause matters more than the swelling. In adults it is usually a kidney stone, an enlarged prostate, a narrowing of the ureter, a tumour pressing from outside, or scarring after surgery or radiotherapy. In pregnancy, mild swelling is common and normal from the growing womb. In babies it is often found on antenatal scans and frequently resolves.

There are two urgent situations.

**An obstructed kidney with infection** is a urological emergency. Antibiotics cannot sterilise urine that has nowhere to go, and the person becomes septic quickly. The treatment is drainage, with a nephrostomy tube through the skin or a stent, and it must not wait.

**Obstruction of both kidneys, or of a single functioning kidney,** causes acute kidney injury and, in complete obstruction, no urine at all. That is also an emergency, and it is most often caused by an enlarged prostate in older men.

Chronic partial obstruction can be silent and destroy a kidney slowly, which is why an incidental finding still needs a cause found.

Signs you might notice

Pain in the side or back, sometimes severe and coming in waves if a stone is the cause.

Fever, chills and feeling very unwell, if infected.

Passing much less urine, or none at all.

Nausea and vomiting.

Blood in the urine.

Difficulty passing urine, a poor stream, or the sense of incomplete emptying, in prostatic obstruction.

Often nothing, with the finding made on a scan done for another reason.

999 or A and E: fever with loin pain; not passing urine at all; or feeling very unwell with any of the above. See sepsis and urinary retention.

Urgent: a rising creatinine with any urinary symptoms.

How it can affect day-to-day life

In older men, gradual prostatic obstruction can cause silent, painless kidney damage over months, sometimes presenting with overflow incontinence and a distended bladder. Anybody with a poor stream and rising creatinine needs a bladder scan, which takes seconds.

Long-term catheters, nephrostomy tubes and ureteric stents all become part of daily life for some people, and each needs practical teaching that is often rushed.

Ureteric stents commonly cause discomfort, urinary urgency and blood in the urine, which is expected rather than a complication, and people are frequently not warned.

Nephrostomy bags need care and can leak or block; a blocked nephrostomy in an obstructed kidney recreates the emergency, so the person needs a number to ring.

Following a resolved obstruction, kidney function may not fully recover, and monitoring continues.

In babies with antenatally detected hydronephrosis, most resolve without intervention, and parents live with months of scans and uncertainty.

Supporting someone well

Treat fever with loin pain as an emergency; an infected obstructed kidney needs drainage, not just antibiotics.

Get anyone who cannot pass urine seen the same hour.

Ask for a bladder scan in any older man with a poor stream and reduced kidney function.

Ask what the cause of the obstruction is; the swelling is a finding, not a diagnosis.

Learn what to do if a nephrostomy or catheter stops draining, and keep the number.

Expect stent discomfort and blood in the urine, and know what would be abnormal.

Keep hydrated, and follow up kidney function after the obstruction is relieved.

For a baby with antenatal hydronephrosis, keep the follow-up scans and ask about antibiotic prophylaxis.

Where to get help

999 or A and E for fever with loin pain, or inability to pass urine.

A GP practice for urinary symptoms and kidney function tests; urology for the cause.

The urology or interventional radiology team for stents and nephrostomies.

Kidney Care UK for support and practical guidance.