Rapid review: renal and genitourinary

• This page is not the place to learn a topic for the first time. It is a revision tool: each block below states the presenting picture, the single most likely diagnosis, the best first test, the best first treatment, the commonest wrong answer, and the full topic to read.
• Renal medicine sorts patients best by mechanism: perfusion, obstruction, glomerular inflammation, tubular injury, interstitial disease, and vascular disease. Working out which mechanism is operating comes before naming a drug.
• The emergencies that kill quickly are the same ones in every setting: hyperkalaemia, infected obstruction or pyelonephritis with sepsis, rapidly progressive glomerulonephritis, and torsion of the testis.
• A normal ultrasound does not exclude renal disease, a normal PSA does not exclude cancer, and a normal creatinine does not mean normal kidney function. If the clinical picture and the laboratory disagree, trust the picture and repeat the test.

By the end of this page you should be able to:

1. Run through the presenting illnesses of renal and genitourinary medicine in examination order, naming the likely diagnosis, the first test, the first treatment and the common trap in each.
2. Spot the red flags that turn a routine presentation into an emergency.
3. Use the flowchart to decide whether a patient needs urgent decompression, urgent immunosuppression, urgent surgery or careful outpatient review.
4. Move from each block to the full MedGrasp topic for depth.

Renal and genitourinary presentations fall into a small number of families: the acutely unwell patient with falling kidney function, blood or protein in the urine, infection, colic, swelling of the scrotum, retention, lower urinary tract symptoms, and silent chronic kidney disease discovered on a routine test. The blocks below take each one in turn and give the answer that an examiner or a busy clinician wants first.

This is a curriculum-gap revision page: it has no single paired chapter in the source syllabus, so it builds only on the full topics named at the end of each block. guideline editions in force here are the KDIGO 2012 AKI materials as summarised in 2013, NICE NG148 (last updated 16 October 2024), NICE NG12 (last updated 15 April 2026), NICE CG97 (reviewed 19 December 2024), the UK Kidney Association hyperkalaemia guideline (updated July 2026), the EAU Urological Infections guideline (2026 limited update), the EAU Urolithiasis guideline (2026), NICE NG131, NICE NG203 and KDIGO 2024 for chronic kidney disease. ^{[1][2][3][4][5][6][7][8][9][10]}

The tests below are the real working kit of renal medicine, and most are cheap.

• Urine dipstick and microscopy. Protein, blood, leucocytes and nitrites give the first clues; microscopy separates glomerular from lower tract bleeding. Dysmorphic red cells and red cell casts mean glomerular disease. ^[1]
• Quantification of proteinuria. A spot protein to creatinine ratio is adequate for mild proteinuria; a 24-hour collection is more reliable when protein loss is heavy. ^[1]
• Renal function. Creatinine with an estimated GFR and electrolytes, compared with previous results. A single abnormal value is not a diagnosis; trends and persistence matter. ^[9][10]
• Bladder scan and renal ultrasonography. Cheap, safe and fast, and they answer the two questions that change management: is there obstruction, and are the kidneys small and scarred? ^[2]
• Electrocardiogram. Essential whenever potassium is raised, because the ECG may warn before the serum result does. ^[5]

The single biggest error in renal medicine is to reach for a diagnosis before excluding the two reversible causes, hypoperfusion and obstruction. The flowchart keeps them first.

• Anuric or oliguric patient with rising creatinine and a distended bladder: decompress before anything else.
• Potassium 6.5 mmol/L or higher, or ECG changes with hyperkalaemia: treat as an emergency. ^[5]
• Fever with loin or flank pain and a stone on imaging: infected obstruction until proven otherwise.
• Sudden testicular pain with a high-riding testis: torsion until proven otherwise.
• Haemoptysis with rapidly rising creatinine and red cell casts: possible pulmonary-renal syndrome.
• Gross haematuria with clots and anaemia: catheter and irrigation, then investigation.

Presenting picture: a patient whose creatinine has risen over days, often after vomiting, diarrhoea, sepsis, a drug, or a procedure, with reduced urine output, or an older man with weak stream who cannot void. The rise is often modest at first and is missed without a baseline. KDIGO defines acute kidney injury as a rise in serum creatinine of at least 0.3 mg/dL (26.5 micromol/L) within 48 hours, a rise to at least 1.5 times baseline within 7 days, or urine output under 0.5 mL/kg per hour for 6 hours. ^[1][2]

Single most likely diagnosis: prerenal (hypoperfusion) acute kidney injury is the commonest mechanism in adult inpatient practice, and in men with prostatic symptoms obstruction from benign prostatic hyperplasia should be excluded before calling it intrinsic renal disease.

Best first test: serum creatinine compared with baseline, electrolytes, urinalysis with sediment, a bladder scan for residual volume and a renal ultrasound to exclude obstruction. ^[1]

When the diagnosis is unclear after the basics, the urine still helps: prerenal disease usually produces concentrated urine with low sodium, while acute tubular injury gives muddy brown granular casts and a higher fractional excretion of sodium. The indices are a guide only and are unreliable after diuretics, contrast or pigment exposure. ^[1]

Best first treatment: stop nephrotoxins, correct volume depletion if present, relieve any obstruction, and treat hyperkalaemia or acidosis if they are present. Dialysis is started for life-threatening complications that medical treatment cannot control. ^[1][2]

Commonest wrong answer: labelling the patient as having acute tubular necrosis before volume status and obstruction have been checked, or giving further nephrotoxins for a fever.

Full topic: renal-genitourinary/acute-kidney-injury

Presenting picture: pink, red or brown urine, either noticed by the patient (visible) or found on a dipstick (non-visible), sometimes with dysuria, sometimes painless. In adults the colour and timing matter: initial, terminal and total haematuria point to different sites. ^[3]

Single most likely diagnosis: in a smoker over 45 with painless visible haematuria, bladder cancer until excluded; in young adults, infection, stones and glomerular disease are all commoner than cancer. ^[3]

Best first test: microscopy to confirm blood in the urine, then renal imaging and cystoscopy according to age and risk, since a dipstick alone is not enough. In the United Kingdom NICE advises a suspected cancer referral for unexplained non-visible haematuria with dysuria or a raised white cell count at age 60 or over. ^[3]

Best first treatment: there is no single drug treatment. Visible haematuria with clots needs catheterisation and bladder irrigation; otherwise the correct treatment is urgent urological assessment on a suspected cancer pathway for unexplained visible haematuria at age 45 or over. ^[3]

Commonest wrong answer: attributing haematuria to warfarin, an antiplatelet drug or a recent urinary tract infection and stopping the search; anticoagulants expose an underlying lesion rather than cause bleeding. ^[3]

Full topic: renal-genitourinary/renal-cell-carcinoma (which covers the approach to haematuria)

Presenting picture: periorbital or ankle oedema, frothy urine, weight gain, and fatigue, sometimes with hypertension, developing over days to weeks. Children often present after a minor infection. ^[1] (definition anchor deferred to the full topic's sources)

The oedema is salt and water retention rather than simple low oncotic pressure, and venous thromboembolism and infection are the dangerous complications that explain most of the mortality. ^[1]

Single most likely diagnosis: in children, minimal change disease; in adults, membranous nephropathy among primary causes, with diabetes, lupus and other secondary causes always to be excluded.

Best first test: quantification of proteinuria, serum albumin, lipids and renal function with urine microscopy, followed by serology for secondary causes; a kidney biopsy is used when the diagnosis is in doubt or in adults.

Best first treatment: treat the underlying cause if one is found, with meticulous supportive care (salt restriction, careful diuresis, ACE inhibition or angiotensin receptor blockade where appropriate, lipid lowering and prophylaxis against venous thromboembolism when indicated) and cause-directed immunosuppression for selected patients.

Commonest wrong answer: prescribing a rapid diuresis without checking intravascular volume, or assuming every child with heavy proteinuria needs a biopsy before a therapeutic trial.

Full topic: renal-genitourinary/nephrotic-syndrome

Presenting picture: cola-coloured or frankly red urine, red cell casts on microscopy, hypertension, mild oedema and mild proteinuria, often after an infection. ^[1]

Complement levels steer the differential: low C3 points to post-infectious, immune-complex or complement-driven disease, while normal C3 and C4 are expected in IgA nephropathy, ANCA disease and anti-GBM disease. ^[1]

Single most likely diagnosis: IgA nephropathy is the commonest finding when biopsy is performed for this syndrome; other possibilities include post-infectious glomerulonephritis, lupus nephritis and ANCA-associated vasculitis. ^[1]

Best first test: urinalysis with microscopy, blood pressure, renal function, complement (C3 and C4) and serology, then kidney biopsy if the diagnosis remains unclear or the decline is rapid.

Best first treatment: control blood pressure and volume, block the renin-angiotensin-aldosterone system, and add cause-directed immunosuppression or plasma exchange when there are crescents or a rapidly progressive course.

Commonest wrong answer: treating the urine as a simple infection because the dipstick is positive for blood, without recognising red cell casts and hypertension as a glomerular problem.

Full topic: renal-genitourinary/nephritic-syndrome

Presenting picture: a patient with a known or suspected renal problem who is confused, weak, palpitated, dyspnoeic or comatose, with a laboratory abnormality that was not there before. Hyperkalaemia, severe hyponatraemia and acidaemia are the three patterns that need immediate attention.

Single most likely diagnosis: hyperkalaemia when potassium is 5.5 mmol/L or higher, classed as mild at 5.5-5.9, moderate at 6.0-6.4 and severe at 6.5 or higher; severe hyponatraemia with seizures or coma when brain adaptation is overwhelmed; and metabolic acidaemia with a low bicarbonate on blood gas testing. ^[5]

Best first test: an electrocardiogram and a repeat serum potassium for hyperkalaemia; paired serum and urine osmolality for hyponatraemia; and an arterial or venous blood gas with calculated anion gap for acid-base disturbance.

The electrocardiogram in hyperkalaemia progresses from peaked T waves through broad QRS complexes to a sine wave; once P waves are lost, the plasma potassium must be assumed to be very high and treated immediately. ^[5]

Commonest wrong answer: correcting a chronic sodium deficit too fast and causing osmotic demyelination, or giving bicarbonate for a respiratory acidosis without addressing ventilation.

Full topics: renal-genitourinary/hyperkalaemia, renal-genitourinary/acid-base-disorders, renal-genitourinary/fluid-and-electrolyte-therapy, renal-genitourinary/hyponatraemia

Presenting picture: dysuria, frequency, urgency and suprapubic discomfort in a woman, sometimes with haematuria and sometimes with fever or flank pain. In men, in pregnancy and in anyone with a catheter or structural abnormality, the infection is not "uncomplicated". ^[6]

Single most likely diagnosis: uncomplicated acute cystitis, usually due to Escherichia coli, when a non-pregnant woman has typical symptoms without fever or flank pain; pyelonephritis when fever and loin pain are present. ^[6]

Best first test: a urine dipstick and, if results are equivocal or risk is high, a mid-stream urine culture before antibiotics. ^[6]

Best first treatment: for uncomplicated cystitis in women, nitrofurantoin monohydrate or macrocrystals 100 mg twice daily for 5 days, or another first-line agent chosen by local resistance; pyelonephritis needs a longer course with an agent that reaches tissue, and hospitalisation when the patient is febrile, pregnant or septic. ^[6]

In men, in pregnancy, with a catheter, or with structural abnormalities, get a culture and look for the cause before calling an infection uncomplicated. ^[6]

Commonest wrong answer: treating asymptomatic bacteriuria, or using nitrofurantoin for suspected pyelonephritis, or forgetting to image a man with infection.

Full topic: renal-genitourinary/urinary-tract-infection

Presenting picture: sudden, severe, colicky loin or flank pain that radiates to the groin, with restlessness, nausea, vomiting and often haematuria, peaking in waves and interspersed with pain-free intervals. Fever and a stone together make this an emergency. ^[7]

Single most likely diagnosis: a calcium-containing stone in the ureter, most often calcium oxalate or calcium phosphate; uric acid, struvite and cystine stones are important variants. ^[7]

Best first test: non-contrast computed tomography of the kidneys, ureters and bladder in adults; renal ultrasonography first in pregnancy and in children and where computed tomography is unavailable. ^[7]

Best first treatment: adequate analgesia, starting with a non-steroidal anti-inflammatory drug where not contraindicated, with antiemetic, hydration as tolerated and an alpha blocker for a distal ureteric stone; infected obstruction needs urgent decompression and antibiotics before any elective procedure. ^[7]

Hydronephrosis on imaging confirms that the stone is causing obstruction; a small non-obstructing stone does not explain severe renal pain. ^[7]

Commonest wrong answer: diagnosing pyelonephritis when the pain is colicky and the fever is absent, or giving opiates alone without an anti-inflammatory, or missing an obstructed infected stone.

Full topic: renal-genitourinary/nephrolithiasis

Presenting picture: usually no symptoms at all. Found on a raised creatinine, a reduced eGFR, albuminuria or an abnormal scan, sometimes with anaemia, fatigue, nocturia or pruritus later. Diabetes and long-standing hypertension are the commonest causes worldwide. ^[9][10]

Single most likely diagnosis: diabetic kidney disease in a patient with diabetes and albuminuria; hypertensive nephrosclerosis in a patient with long-standing hypertension and small kidneys; the diagnosis is clinical and confirmed by staging rather than by a single biopsy.

Best first test: repeat serum creatinine to confirm a reduced eGFR persists, plus a urinary albumin to creatinine ratio, and renal ultrasonography for structure and size. ^[9][10]

Best first treatment: control blood pressure, block the renin-angiotensin-aldosterone system where albuminuria is present, add an SGLT2 inhibitor where appropriate, treat cardiovascular risk, and refer to nephrology when advanced or progressing. ^[9]

Refer when the eGFR is below 30, when albuminuria is heavy or increasing, or when the kidney function falls faster than expected. ^[9][10]

Commonest wrong answer: calling a single episode of reduced eGFR chronic kidney disease without persistence, or stopping an ACE inhibitor or ARB for a small creatinine rise that is expected and stabilises.

Full topic: renal-genitourinary/chronic-kidney-disease

Presenting picture: sudden, severe testicular pain with swelling, often waking the patient from sleep, with nausea or vomiting. The testis is high riding and lies horizontally, pain is not relieved by elevation, and the scrotum may be red. ^[2] (sources: StatPearls and family; see the full topic)

Single most likely diagnosis: testicular torsion within the first hours; epididymitis or orchitis afterwards, when pain is more gradual and localised to the epididymis. ^[2]

Best first test: do not wait for imaging if the diagnosis is clinically likely. Colour Doppler ultrasonography is useful when the presentation is unclear or delayed; reduced or absent blood flow supports torsion. ^[2]

Best first treatment: urgent surgical exploration and detorsion with bilateral orchidopexy, after manual detorsion if immediate surgery is delayed; analgesia and scrotal support are adjuncts, not treatment. ^[2]

Lifting the scrotum may relieve pain in epididymitis but not in torsion, although this sign is unreliable; when torsion is possible, arrange surgery rather than trust a physical sign. ^[2]

Commonest wrong answer: treating with antibiotics and discharging with a diagnosis of epididymitis in a young man whose pain began suddenly in the night, or delaying exploration for an ultrasound in an obvious torsion.

Full topic: renal-genitourinary/scrotal-swelling

Presenting picture: sudden, usually painful, inability to pass urine with a palpable or percussible bladder and distress. Chronic retention is the opposite: a large painless bladder, poor stream, overflow dribbling, raised residual volume and, eventually, renal impairment. ^[4]

Single most likely diagnosis: in an older man, acute urinary retention from bladder outlet obstruction due to benign prostatic hyperplasia; in women, look for pelvic organ prolapse, a stone, a stricture, a drug or a neurological cause. ^[4]

Best first test: a bladder scan for post-void residual volume; add urea and electrolytes and creatinine, urinalysis and renal ultrasonography when chronic retention or renal impairment is suspected. ^[4]

Best first treatment: immediate catheterisation to decompress a painful acute retention, followed by an alpha blocker before removing the catheter; after decompression, replace only part of the high urine output and monitor electrolytes. ^[4]

After decompression, urine output can stay high for a day or two; replace only part of the output and replete electrolytes rather than matching it litre for litre. ^[4]

Commonest wrong answer: removing the catheter without an alpha blocker, or matching post-obstructive diuresis litre for litre with intravenous fluid and causing electrolyte loss and cerebral oedema.

Full topic: renal-genitourinary/urinary-retention

Presenting picture: a man with a weak stream, hesitancy, terminal dribbling, incomplete emptying, nocturia, frequency or urgency, sometimes with an episode of retention. ^[4]

Single most likely diagnosis: benign prostatic hyperplasia with benign prostatic obstruction and lower urinary tract symptoms, once infection, cancer, a stone and a stricture have been excluded. ^[4]

Best first test: urinalysis, prostate-specific antigen with shared decision making, measurement of flow rate and post-void residual volume, and ultrasonography of the kidneys and bladder. ^[4]

Best first treatment: an alpha blocker for bothersome symptoms, add a 5-alpha reductase inhibitor if the prostate is enlarged on imaging, and offer transurethral resection or an equivalent procedure for complications or failed medication. ^[4]

Commonest wrong answer: treating an elevated prostate-specific antigen as prostatitis without excluding cancer, or starting medication without measuring symptom burden with a validated score.

Full topic: renal-genitourinary/benign-prostatic-hyperplasia

Presenting picture: usually no symptoms at all. Found on a raised prostate-specific antigen, a hard or nodular prostate on rectal examination, or the investigation of lower urinary tract symptoms. Metastatic disease may present with bone pain, weight loss or obstructive uropathy. ^[8]

Single most likely diagnosis: adenocarcinoma of the prostate in a man with an abnormal rectal examination or a significantly raised prostate-specific antigen, with risk stratification by stage and grade. ^[8]

Best first test: multiparametric magnetic resonance imaging as the first-line investigation for suspected clinically localised disease, with targeted or systematic biopsy when the Likert score is 3 or more. ^[8]

Best first treatment: matched to risk: active surveillance for low-risk localised disease, radical prostatectomy or radiotherapy for localised disease, and androgen deprivation therapy with appropriate intensification for advanced disease. ^[8]

Commonest wrong answer: diagnosing cancer on prostate-specific antigen alone, or excluding cancer because the prostate-specific antigen is normal, or treating a screen-detected low-risk cancer that would be better observed.

Full topic: renal-genitourinary/prostate-cancer

• Run through the two reversible causes first: hypoperfusion and obstruction. ^[1][2]
• Painless visible haematuria in a patient aged 45 or over needs a suspected cancer pathway, and anticoagulants do not "cause" haematuria. ^[3]
• Minimal change disease is the likely diagnosis in a child with nephrotic syndrome; membranous nephropathy is the commonest primary cause in older adults. ^[1]
• IgA nephropathy is the commonest biopsy finding in nephritic syndrome; complement pattern steers the differential. ^[1]
• Hyperkalaemia of 5.5 mmol/L or higher needs an ECG and treatment in parallel, not in series. ^[5]
• Uncomplicated cystitis in women is treated with nitrofurantoin 100 mg twice daily for 5 days. ^[6]
• Fever with a urinary stone is infected obstruction until proven otherwise. ^[7]
• Chronic kidney disease needs persistence of abnormality, not a single raised creatinine. ^[9][10]
• Sudden testicular pain is torsion until proven otherwise. ^[2]
• Acute urinary retention is decompressed immediately, then treated with an alpha blocker before catheter removal. ^[4]
• Prostate-specific antigen above a threshold is not a diagnosis; imaging and biopsy stage the disease. ^[8]

• renal-genitourinary/acute-kidney-injury
• renal-genitourinary/renal-cell-carcinoma (includes the approach to haematuria)
• renal-genitourinary/nephrotic-syndrome
• renal-genitourinary/nephritic-syndrome
• renal-genitourinary/hyperkalaemia
• renal-genitourinary/acid-base-disorders
• renal-genitourinary/fluid-and-electrolyte-therapy
• renal-genitourinary/hyponatraemia
• renal-genitourinary/urinary-tract-infection
• renal-genitourinary/nephrolithiasis
• renal-genitourinary/chronic-kidney-disease
• renal-genitourinary/scrotal-swelling
• renal-genitourinary/urinary-retention
• renal-genitourinary/benign-prostatic-hyperplasia
• renal-genitourinary/prostate-cancer