Synopsis
Use symptoms, risk factors, medicines and focused examination to distinguish acute from chronic kidney disease, detect obstruction or systemic nephritis and identify immediate physiological danger.
- Start with time course and baseline: hours to days suggests acute kidney injury, whereas abnormalities persisting for at least three months support chronic kidney disease; an acute-on-chronic picture is common.
- Quantify urine change rather than accepting 'passing less': ask usual and current volume, frequency, nocturia, stream, hesitancy, incomplete emptying, retention, catheter output and recent fluid losses.
- Visible blood, froth, smoky urine, dysuria, flank pain, colic and fever localise different pathways. Painless visible haematuria still needs cancer-pathway assessment even when anticoagulated.
- Ask about diabetes, hypertension, vascular disease, recurrent infection or stones, autoimmune symptoms, malignancy, pregnancy, recent sepsis, surgery, contrast, travel and family kidney history.
- Reconcile every medicine and non-prescribed product: NSAIDs, ACE inhibitor or ARB, diuretics, antimicrobials, proton-pump inhibitors, lithium, calcineurin inhibitors, supplements and recreational drugs can change risk.
- Volume assessment is a synthesis, not one sign. Weight trend, mucous membranes, capillary refill, pulse, lying and standing blood pressure, JVP, oedema and lung fields can disagree.
- Look beyond the kidneys for mechanism: rash, purpura, synovitis, sinus or lung disease, neuropathy, haemoptysis, endocarditis stigmata and retinal changes can reveal systemic glomerulonephritis or vasculitis.
- Palpate for a distended bladder and examine for loin or graft tenderness. A normal abdominal examination does not exclude upper-tract obstruction, particularly when obstruction is early or unilateral.
- In established kidney failure, inspect fistula or graft access without cannulating it casually, listen for a bruit where trained, and protect that limb from avoidable venepuncture and blood-pressure cuffs.
- Finish with a one-line problem representation: acuity, urine output, volume/perfusion, likely pre-renal/intrinsic/post-renal mechanism, complications and the next action.
Key red flags
Thirst, vomiting, diarrhoea, bleeding, poor intake or high-output stoma with weight loss, postural symptoms, cool peripheries and low JVP supports reduced effective perfusion, but beta-blockers and older age can blunt tachycardia.
Rapid weight gain, orthopnoea, raised JVP, basal crackles, ascites and peripheral oedema suggest venous congestion or heart failure. Intravascular and interstitial volume cannot be inferred from ankle oedema alone.
Smoky urine, oedema, hypertension, proteinuria, haematuria and reduced function, especially with purpura, arthritis, haemoptysis or sinus disease, suggests nephritic disease requiring prompt nephrology discussion.
Anuria, intermittent stream, hesitancy, palpable bladder, loin pain, pelvic malignancy, stones, recent instrumentation or neurogenic symptoms supports outflow or upper-tract obstruction. Sepsis plus obstruction is a drainage emergency.
Painless visible haematuria, recurrent unexplained urinary bleeding, weight loss, persistent loin pain or a mass needs age- and symptom-specific NICE referral assessment; anticoagulation does not provide a sufficient explanation.
Investigation priorities
Establish direction, acuity and life-threatening biochemical complications.
Management branches
Oliguria, rapid creatinine rise, hypotension, respiratory distress, confusion or suspected severe electrolyte disturbance.
- Perform ABCDE, check observations, ECG and bedside glucose, obtain urgent U&E and venous blood gas, and measure actual urine output with a catheter only when indicated.
- Assess depletion versus congestion, stop or hold clearly unsafe medicines after indication review, and treat sepsis, hyperkalaemia, pulmonary oedema or shock through the appropriate protocol.
- Exclude obstruction promptly and seek nephrology or urology advice early for anuria, severe complications, unclear intrinsic AKI or failure to respond to initial treatment.