Clinical Guides
Acute Kidney Injury
A source-grounded guide to detecting, staging and treating acute kidney injury, with cause-directed fluid and medicine decisions, dialysis triggers, recovery follow-up and India-specific infection, toxin, access and referral safeguards.
MedNext Academy | 15 min read
Acute Kidney Injury
A source-grounded guide to detecting, staging and treating acute kidney injury, with cause-directed fluid and medicine decisions, dialysis triggers, recovery follow-up and India-specific infection, toxin, access and referral safeguards.
Summary
Acute kidney injury (AKI) is an abrupt reduction in kidney function detected by a rise in serum creatinine, reduced urine output, or both. KDIGO defines AKI as a creatinine increase of at least 0.3 mg/dL within 48 hours, a rise to at least 1.5 times a known or presumed baseline within seven days, or urine output below 0.5 mL/kg/hour for six hours. Stage by the worse creatinine or urine criterion. Stage 1 is creatinine 1.5 to 1.9 times baseline or a rise of at least 0.3 mg/dL, or urine below 0.5 mL/kg/hour for 6 to 12 hours. Stage 2 is creatinine 2.0 to 2.9 times baseline or that urine rate for at least 12 hours. Stage 3 is creatinine at least 3 times baseline, at least 4.0 mg/dL, kidney replacement therapy, or in patients younger than 18 a fall in eGFR below 35 mL/min/1.73 m²; urine criteria are below 0.3 mL/kg/hour for at least 24 hours or anuria for at least 12 hours. Creatinine lags behind injury and oliguria requires confirmation.
Treat AKI as a syndrome, not a final diagnosis. Stabilise airway, breathing and circulation; identify sepsis, haemorrhage, shock, obstruction, nephrotoxins, glomerular inflammation and complications. Reconstruct the baseline creatinine, measure urine accurately, perform urinalysis and microscopy where available, review every medicine and image the urinary tract when obstruction is possible or the cause remains unclear.
Fluid is a prescribed treatment: give an appropriate crystalloid only when hypovolaemia or fluid responsiveness is plausible, reassess after each intervention, and stop when perfusion is restored or congestion appears. Do not use diuretics to reverse kidney injury; use them selectively for fluid overload. Dialysis is started for life-threatening electrolyte, acid-base, fluid or uraemic complications, not for an isolated creatinine number. Arrange follow-up because incomplete recovery predicts chronic kidney disease. The KDIGO 2012 guideline remains the final international AKI guideline while a 2026 update is still a public-review draft; current current guidelines (2024) recommendations supplement recognition and referral but are not Indian prescribing policy.
How Common Is It?
AKI is common across emergency departments, medical and surgical wards, intensive care, obstetrics and community acute illness, but estimates depend strongly on population and surveillance. current guidelines reports that AKI is identified in roughly 13% to 18% of hospital admissions in its UK context. That figure should not be transferred to India as a national prevalence estimate: baseline testing, laboratory access, admission thresholds, referral patterns and case mix differ. Community-acquired episodes may be missed when no previous creatinine exists, and urine-output criteria are often unavailable outside monitored beds.
Burden is highest among people with sepsis, major surgery, shock, heart or liver failure, chronic kidney disease, diabetes, malignancy and critical illness. In India, monsoon-associated dehydration and infections, gastroenteritis, malaria, dengue, leptospirosis, scrub typhus, obstetric emergencies, snakebite, envenomation, rhabdomyolysis, traditional remedies and unregulated drug exposure can contribute alongside globally common causes. The relative importance varies by district and season; a single epidemiological list must not replace local diagnostic reasoning.
AKI is clinically important even when creatinine later improves. It is associated with mortality, prolonged admission, medicine toxicity, recurrent AKI and later chronic kidney disease. Severity, duration and repeated episodes matter, but apparent stage 1 disease can still signal serious infection, glomerulonephritis or obstruction. Conversely, a transient creatinine change caused by laboratory variation or haemodilution must be interpreted in context. Services should audit stage, cause, dialysis, recovery and follow-up rather than merely count coded discharges. This guide therefore emphasises reliable case recognition and outcome ownership rather than an unsupported Indian incidence claim.
Risk Factors
Reduced renal reserve increases susceptibility. Important background factors include chronic kidney disease, previous AKI, older age, diabetes, hypertension, heart failure, cirrhosis, nephrotic disease, myeloma, malignancy, peripheral vascular disease and a solitary or transplanted kidney. Pregnancy adds distinct risks such as haemorrhage, sepsis, hypertensive disorders, acute fatty liver and thrombotic microangiopathy. Children, frail adults and people unable to maintain oral intake may deteriorate rapidly. A normal historical creatinine does not remove risk during severe physiological stress.
Acute exposures include sepsis, diarrhoea, vomiting, fever, haemorrhage, burns, pancreatitis, major surgery, hypotension, anaesthesia, cardiogenic shock and sustained hypoxaemia. Urinary obstruction may arise from stones, prostate disease, pelvic malignancy, blood clots, neurogenic bladder or blocked catheters. Intrinsic injury follows ischaemia, infection, glomerulonephritis, interstitial nephritis, pigment nephropathy, thrombotic microangiopathy and selected toxins. India-relevant histories should ask about febrile illness, contaminated water, snakebite, pesticide or chemical exposure, herbal and traditional preparations, and medicines purchased without prescription.
Medicine-associated risk is contextual rather than a simplistic blacklist. NSAIDs, renin-angiotensin system blockers, diuretics, aminoglycosides, amphotericin, vancomycin, calcineurin inhibitors, antivirals, chemotherapy and iodinated contrast can contribute through different mechanisms. Combinations become hazardous during hypovolaemia or sepsis. Contrast-associated AKI risk must be balanced against the harm of delaying essential imaging; current criteria are jurisdiction-specific and do not justify cancelling a lifesaving scan automatically.
Progression risk rises with persistent hypotension, ongoing infection, repeated nephrotoxic exposure, delayed obstruction relief and absent monitoring. Limited transport, laboratory delays, unaffordable repeat tests and unavailable dialysis can convert moderate injury into a preventable emergency. Record these access risks in the clinical plan.
Diagnosis
Diagnosis requires confirmation of the AKI time course, immediate staging and an active search for cause. A computer alert is a prompt to assess the patient, not a diagnosis by itself.
History
Establish recent urine volume, thirst, diarrhoea, vomiting, fever, rigors, bleeding, surgery, trauma, exertion, seizures, muscle pain, flank pain, colic, dysuria, retention, rash, arthralgia, haemoptysis and swelling. Ask about pregnancy and postpartum events. Reconstruct previous creatinine and weight. List prescribed, over-the-counter, injected, herbal and traditional products with start dates, recent contrast and antibiotics. Document diabetes, hypertension, kidney, cardiac, liver, autoimmune, malignant and urological disease, travel, floods, animals, snakebite and occupational toxins.
Examination
Measure temperature, pulse, blood pressure including trends, respiratory rate, oxygen saturation, perfusion, mental state and weight. Seek dry mucosa, postural symptoms and capillary refill, but also raised venous pressure, oedema, crackles, ascites and signs of cardiac failure because oedematous patients can have poor effective perfusion. Examine for sepsis source, rash, purpura, arthritis, livedo, jaundice, muscle tenderness, bladder distension and costovertebral tenderness. Confirm catheter patency before diagnosing oliguria.
Investigations
Repeat creatinine, urea, electrolytes, bicarbonate, glucose, calcium, phosphate, CBC and urinalysis; add blood gas, lactate, liver tests, creatine kinase, haemolysis studies and cultures according to presentation. Quantify urine output and protein, and examine sediment for dysmorphic red cells, casts, crystals or tubular cells when expertise exists. Ultrasound kidneys and bladder urgently if obstruction is suspected and within an appropriate early window when cause is unclear. Serology for ANCA, anti-GBM antibody, ANA, complement, infection or monoclonal disease is targeted to an active sediment or systemic clues. Kidney biopsy is specialist-directed when intrinsic disease is unexplained or rapidly progressive and the result will change treatment.
Differential Diagnosis
First distinguish true AKI from chronic kidney disease, acute-on-chronic disease and a misleading creatinine result. Small echogenic kidneys, longstanding anaemia, mineral-bone disturbance and old laboratory results support chronicity but are not absolute; kidney size may remain normal in diabetes, infiltrative disease or early CKD. Low muscle mass can conceal severe dysfunction, while creatine supplements, cooked meat, trimethoprim or inhibited tubular secretion may raise creatinine without equivalent structural injury. Dilution after fluid resuscitation can mask a rise. Repeat sampling and clinical chronology are essential.
Pre-renal physiology includes volume loss, vasodilatation, sepsis, cardiac failure, tamponade and hepatorenal physiology. It can progress to tubular injury, and response to a fluid challenge is neither a safe universal test nor proof of diagnosis. Intrinsic causes include acute tubular injury, glomerulonephritis, interstitial nephritis, vascular occlusion, malignant hypertension, thrombotic microangiopathy, cortical necrosis and pigment or crystal nephropathy. Fractional excretion indices are affected by diuretics, CKD, sepsis and timing; they support but do not settle causation.
Post-renal AKI includes bladder outlet obstruction, bilateral ureteric obstruction or unilateral obstruction in a solitary functioning kidney. Absence of hydronephrosis early, in retroperitoneal fibrosis or with dehydration does not completely exclude it. Urinary catheter blockage can imitate renal oliguria.
Systemic mimics and mixed causes are common. Sepsis may cause haemodynamic and tubular injury together; dengue may combine capillary leak, shock and rhabdomyolysis; malaria, leptospirosis and snakebite have multiple renal mechanisms. Pulmonary oedema may reflect cardiac failure with cardiorenal syndrome rather than simple fluid excess. Haematuria from catheter trauma or menstruation is not automatically glomerulonephritis. A useful final assessment states the stage, time course, leading mechanism, complications, evidence for alternatives and what observation will discriminate them.
Management
Stabilise immediately. Treat sepsis, haemorrhage, hypoxaemia, arrhythmia and obstruction in parallel with kidney assessment. Obtain cultures before antimicrobials when this causes no dangerous delay, then use the current local sepsis and antibiogram pathway. Monitor observations, mental state, urine output, fluid input, weight and laboratory trends at a frequency proportionate to severity. Insert a urinary catheter only when accurate output or obstruction management justifies infection and trauma risk; confirm patency and remove it promptly when no longer needed.
Assess fluid status repeatedly. If hypovolaemia is likely, give a measured isotonic crystalloid intervention appropriate to age and comorbidity, then reassess blood pressure, perfusion, lungs, venous congestion and urine response. Continued blind boluses in oliguria can cause pulmonary and tissue oedema. If congested, stop unnecessary fluid and treat the underlying cardiac, hepatic or critical illness; a loop diuretic may relieve overload but does not shorten intrinsic AKI. Vasopressors belong in monitored shock care after appropriate volume assessment.
Stop or withhold avoidable nephrotoxins, reconcile every dose to current kidney function and drug levels, and preserve necessary therapy when benefit outweighs risk. Relieve obstruction urgently through urology or interventional pathways. Treat glomerular, interstitial, vascular, infectious, pigment and pregnancy-related causes with specialists rather than empirical corticosteroids. Manage potassium, acid-base disturbance, glucose, nutrition and infection without excessive potassium, phosphate, sodium or fluid restriction unrelated to measured need.
Discuss kidney replacement therapy early when complications are approaching. Start emergently for refractory dangerous hyperkalaemia, severe metabolic acidosis not correctable safely, pulmonary oedema or fluid overload compromising oxygenation, selected toxin removal, or uraemic complications such as encephalopathy, pericarditis or bleeding. Creatinine and urea values alone do not define the moment. Plan vascular access, modality, anticoagulation and transfer according to haemodynamics, resources and likely duration. Review recovery after discharge, including creatinine, urine protein, blood pressure and medicines.
Prescribing Information
Medication reconciliation is a treatment, not clerical work. Record each prescribed, non-prescription, contrast, herbal and traditional exposure, its last dose and indication. Review agents that affect perfusion, accumulate in reduced clearance, raise potassium, cause interstitial nephritis or direct tubular toxicity. Temporarily withholding a renin-angiotensin blocker, diuretic or other medicine during shock or major volume depletion may be appropriate, but indefinite discontinuation after recovery can deprive a patient of cardiac or renal benefit. Specify restart criteria, responsible clinician and monitoring.
Dose antimicrobials and other renally cleared drugs using the local pharmacy method, recognising that creatinine-based estimates are unreliable when function changes rapidly. Loading doses may still be needed in severe infection, while maintenance interval or dose requires review. Therapeutic drug monitoring is important for selected aminoglycosides, glycopeptides and narrow-index medicines. Avoid duplicate NSAIDs and combinations of nephrotoxins where alternatives exist. Metformin, insulin, anticoagulants, opioids, gabapentinoids, digoxin, colchicine and many antivirals require specific toxicity assessment; no generic list substitutes for the current formulary.
Hyperkalaemia is treated through a monitored emergency protocol with ECG assessment, membrane stabilisation when indicated, intracellular shift, potassium removal and repeated testing. Do not assume a temporary shift removes potassium. Sodium bicarbonate is not a routine AKI cure; use follows a defined acid-base indication. Diuretics are for congestion, not renal recovery, and can worsen volume depletion. Low-dose dopamine, fenoldopam and routine natriuretic strategies are not recommended as renal-protective treatments by KDIGO.
Contrast decisions should consider diagnostic urgency, current kidney status, route, dose and alternatives. Do not delay a time-critical scan because of an unverified fear, and do not promise that hydration eliminates risk. Before discharge, reconcile stopped and restarted medicines, arrange repeat renal and potassium testing, warn against unsupervised NSAIDs and ensure the patient knows who will interpret results.
When to Refer
Discuss urgently with nephrology or a critical-care service when AKI is stage 3, progressing rapidly, has no clear cause, follows a transplant, is accompanied by active urinary sediment or significant proteinuria, or causes refractory electrolyte, acid-base, uraemic or fluid complications. Suspected vasculitis, anti-GBM disease, lupus nephritis, thrombotic microangiopathy, interstitial nephritis or myeloma kidney requires an expedited diagnostic plan. Do not delay transfer for a full local serology panel when rapidly progressive disease or dialysis need is likely.
Refer immediately to urology for an infected obstructed system, bilateral obstruction, obstruction in a solitary functioning kidney, anuria with retention, traumatic catheter failure or a blocked upper tract with deteriorating physiology. Decompression is source control; antibiotics and fluid alone are not adequate for infected obstruction. Obstetric, toxicology, infectious-disease, haematology and rheumatology input is added according to the cause, without fragmenting ownership.
Emergency transfer is required for shock, severe hypoxaemia from pulmonary oedema, refractory hyperkalaemia, severe acidosis, uraemic encephalopathy or pericarditis, seizures, major bleeding, suspected toxin requiring extracorporeal removal, or a setting unable to measure potassium and urine output safely. Contact the receiving unit before transport, state likely dialysis need and continue stabilisation.
Current guidelines advises nephrology discussion within 24 hours for specified higher-risk or uncertain presentations and follow-up referral after recovery when eGFR remains substantially reduced; these are useful service benchmarks, not automatically Indian referral mandates. In India, travel time, dialysis availability and laboratory turnaround should lower the escalation threshold. A usable referral includes baseline and serial creatinine, stage, urine output, potassium, bicarbonate or blood gas, fluid balance, medicines, infection treatment, urinalysis, imaging and transport risks.
Red Flags
Life-threatening AKI complications require action before the exact cause is known. ECG change or severe potassium elevation, worsening metabolic acidosis, pulmonary oedema with hypoxaemia, uraemic encephalopathy, pericarditic chest pain or rub, uncontrolled bleeding, seizures, profound oliguria or anuria and rapidly worsening biochemical abnormalities demand monitored emergency treatment and dialysis assessment. A patient can require kidney replacement therapy before reaching an arbitrary urea or creatinine threshold.
Shock signs include hypotension, altered consciousness, cool or mottled skin, delayed capillary refill, rising lactate and falling urine output. Sepsis, haemorrhage and cardiogenic failure need different source treatment, so repeated indiscriminate fluid can be harmful. Fever with flank pain and obstruction is a urological emergency. Bladder distension with anuria requires catheter assessment or decompression expertise; absence of pain does not make obstruction safe.
Haematuria plus proteinuria, red-cell casts, pulmonary haemorrhage, purpura, severe hypertension, thrombocytopenia, haemolysis, neurological change or a fast creatinine rise suggests glomerular or vascular disease. ANCA and anti-GBM results and biopsy planning must not delay specialist-led treatment in a compatible rapidly progressive syndrome. New rash, eosinophilia and systemic features after a medicine may indicate interstitial nephritis, but their absence does not exclude it.
Dark urine after crush injury, seizures, heat illness, statin toxicity or snakebite raises pigment injury; measure creatine kinase and treat the systemic cause. Pregnancy or postpartum AKI with hypertension, haemolysis, thrombocytopenia, haemorrhage or sepsis needs emergency obstetric and renal care. After discharge, breathlessness, reduced urine, swelling, confusion, weakness, vomiting, palpitations or recurrent fever warrants urgent reassessment rather than waiting for a routine creatinine appointment.
Indian Clinical Context
India combines high-volume tertiary nephrology with districts where creatinine, potassium, ultrasound, microscopy and acute dialysis are intermittently available. Management must therefore identify which information changes immediate care and when transfer is safer than local delay. A peripheral facility can recognise AKI, stage it, check glucose and ECG, treat shock or sepsis, stop avoidable nephrotoxins, measure output and exclude simple catheter obstruction while arranging a monitored transfer. It should not postpone referral while pursuing unavailable biomarkers or a complete serology panel.
The cause profile is locally variable. Ask specifically about diarrhoeal dehydration, tropical febrile illness, malaria, dengue, leptospirosis, scrub typhus, severe bacterial infection, obstetric haemorrhage or hypertension, snakebite, heat and exertion, pesticides, unlabelled remedies and over-the-counter analgesics or antibiotics. Use ICMR, NCDC, state and institutional infection protocols where applicable, including current antibiograms; KDIGO and international guidelines do not supply an Indian empirical antimicrobial regimen. Test selection follows season, geography and exposure rather than a universal fever panel.
Dialysis capacity, modality, blood-product access, ICU beds and transport differ. Decide early whether intermittent haemodialysis, prolonged intermittent therapy, continuous therapy or peritoneal dialysis is actually available and clinically suitable. Modality choice is based on physiology, expertise and resources; delayed transfer after complications are established is not resource stewardship. Discuss costs and public pathways openly without allowing affordability to become an undocumented clinical exclusion.
Patients may arrive after partial fluid, antibiotics, diuretics or traditional preparations. Ask without blame, retain packaging when possible and avoid claiming causation from chronology alone. Discharge plans must be feasible: give the last creatinine and stage in writing, list medication changes and restart checks, arrange an affordable laboratory and named result owner, and explain that symptomatic improvement does not prove renal recovery. No national Indian AKI incidence or universal dialysis threshold is asserted in this draft.
NMC Competency Mapping
NMC CBME 2024 Pathology competency PA28.3 asks learners to define and describe the aetiology, precipitating factors, pathogenesis, pathology, laboratory urinary findings, progression and complications of acute renal failure, the older term closely corresponding to severe AKI. This guide extends that pathology foundation into contemporary KDIGO definition, staging, bedside evaluation and safe escalation. Learners should distinguish a syndrome definition from aetiology and recognise that creatinine and urine-output criteria may assign different stages.
A competent undergraduate should reconstruct baseline renal function, calculate the relative creatinine change, measure urine output over time and classify likely pre-renal, intrinsic and post-renal mechanisms while acknowledging overlap. They should interpret dipstick and sediment, recognise haematuria plus proteinuria as possible nephritis, request ultrasound for suspected obstruction and identify when serology or biopsy needs nephrology supervision. Biochemistry integration includes potassium, bicarbonate, urea, creatinine and limitations of eGFR during non-steady state.
Pharmacology competence includes medication reconciliation, nephrotoxin stewardship, renal dose review and prevention of dangerous accumulation. Medicine, surgery, paediatrics, obstetrics, anaesthesia, emergency care and microbiology contribute cause-specific contexts. The learner should reassess after a measured fluid intervention rather than write automatic litres, and should explain why diuretics do not repair acute tubular injury.
For skills and communication, students should document stage, fluid balance, current medicines, infection treatment and referral urgency; communicate a critical potassium result; and provide a recovery plan. They must recognise dialysis indications conceptually without independently prescribing a modality. Curriculum mapping does not certify this quarantined draft, confer nephrology competence or replace institutional emergency protocols and supervision.
Key Exam Pearls for NEET PG
KDIGO AKI is diagnosed by any of three routes: creatinine rise at least 0.3 mg/dL within 48 hours, creatinine at least 1.5 times baseline within seven days, or urine output below 0.5 mL/kg/hour for six hours. Stage by the most severe creatinine or output criterion; kidney replacement therapy makes it stage 3. Serum creatinine is delayed and eGFR equations are unreliable during rapidly changing function. Oliguria demands confirmation of measurement and catheter patency.
Classify mechanisms as haemodynamic, intrinsic renal or obstructive, but expect mixtures. Urinalysis with blood and protein suggests nephritis; muddy granular casts support tubular injury; red-cell casts support glomerular bleeding, while a bland sediment does not exclude important disease. Fractional sodium excretion is confounded by diuretics, CKD and sepsis. Ultrasound is central when obstruction is possible, yet very early obstruction may lack marked dilatation.
Fluid is indicated for suspected hypovolaemia, followed by immediate reassessment. Pulmonary congestion is a reason to stop, not to chase urine with more fluid. Loop diuretics treat overload, not the kidney lesion. Review NSAIDs, renin-angiotensin blockers, diuretics, antimicrobials and all renally cleared drugs, but plan appropriate restart after recovery.
Remember dialysis for refractory potassium, acidosis, fluid overload or pulmonary oedema, selected toxins and uraemic complications; no isolated creatinine level is a universal trigger. Treat infected obstruction by urgent drainage plus antimicrobials. Rapid creatinine rise with haematuria, proteinuria, pulmonary haemorrhage or systemic vasculitis features demands urgent nephrology and possible biopsy. Follow-up after AKI is part of management because recovery may be incomplete and future CKD risk remains.
Frequently Asked Questions
Does every creatinine rise mean structural kidney damage?
No. Creatinine can change with fluid balance, muscle injury, meat or supplement intake, assay variation and medicines that reduce tubular secretion. Nevertheless, a change meeting AKI criteria must be treated as clinically important until its timing and cause are understood. Repeat the measurement, reconstruct baseline values, assess urine output and examine the patient. A seemingly functional change can coexist with sepsis, obstruction or intrinsic injury, so the explanation must fit the whole presentation rather than one laboratory value.
Should an oliguric patient automatically receive intravenous fluid?
No. Oliguria may result from hypovolaemia, shock, congestion, obstruction or intrinsic kidney injury. Confirm measurement and catheter patency, then assess perfusion and fluid overload. A measured crystalloid intervention is reasonable when hypovolaemia is plausible, with immediate reassessment. Continued fluid despite rising venous pressure, crackles, oedema or absent physiological benefit can worsen pulmonary oedema. Fluid should have an indication, amount, review time and stop criteria just like any other prescription.
When is dialysis started in acute kidney injury?
Dialysis or another kidney replacement modality is started urgently for life-threatening complications such as refractory dangerous hyperkalaemia, severe acidosis that cannot be corrected safely, pulmonary oedema or fluid overload compromising oxygenation, selected dialysable toxins, and uraemic encephalopathy, pericarditis or bleeding. The decision also considers trajectory, catabolism, haemodynamics and available modality. A single creatinine or urea number is not a universal trigger. Early nephrology discussion and transfer matter when local dialysis is unavailable.
What follow-up is needed after apparent recovery from acute kidney injury?
Record the highest AKI stage, likely cause, dialysis exposure, discharge creatinine and unresolved urine abnormalities. Arrange repeat creatinine, electrolytes, blood pressure and urine protein assessment at an interval based on recovery and risk, with a named clinician responsible for results. Reconcile medicines and state when withheld drugs should be reconsidered. Persistent dysfunction, proteinuria, haematuria or recurrent episodes need renal review. Patients should avoid unsupervised NSAIDs and seek early care during vomiting, diarrhoea, fever, reduced urine, swelling or breathlessness.
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