Signs and Symptoms of Acute Kidney Injury
Acute kidney injury is often clinically silent in its early stages, with most patients being asymptomatic until significant kidney dysfunction develops; the diagnosis is primarily made through laboratory criteria rather than clinical symptoms. 1
Diagnostic Criteria (Laboratory-Based Detection)
AKI is defined by objective laboratory and urine output criteria rather than symptoms 1:
- Serum creatinine increase of ≥0.3 mg/dL (26.5 μmol/L) within 48 hours 1, 2
- Serum creatinine increase to ≥1.5 times baseline within 7 days 1, 3
- Urine output <0.5 mL/kg/hour for 6 hours 1, 4
The KDIGO staging system classifies severity based on these criteria, with Stage 1 being the mildest and Stage 3 the most severe 1. Importantly, many patients with AKI have no symptoms at all and are identified only through routine laboratory monitoring 5.
Clinical Manifestations When Present
Volume and Electrolyte-Related Signs
When symptoms do occur, they typically reflect fluid and electrolyte disturbances 6:
- Oliguria (reduced urine output) - though non-oliguric AKI is common 3, 7
- Edema - particularly in dependent areas when volume overload develops 1
- Hypertension - from fluid retention 1
- Signs of volume depletion - in prerenal AKI, including orthostatic hypotension, dry mucous membranes, decreased skin turgor 2, 3
Uremic Symptoms (Advanced AKI)
These manifest when kidney dysfunction is severe 6:
- Nausea and vomiting 6
- Altered mental status, confusion, or lethargy - from uremic encephalopathy 3, 7
- Weakness and fatigue 6
- Muscle cramps 6
- Anorexia 6
Electrolyte Imbalance Symptoms
Patients may develop signs related to specific electrolyte derangements 6:
- Hyperkalemia manifestations - muscle weakness, cardiac arrhythmias 3, 7
- Metabolic acidosis symptoms - rapid breathing, confusion 3
- Hypocalcemia - rarely tetany 6
Physical Examination Findings
The physical examination should focus on specific findings 1, 3:
- Volume status assessment - jugular venous pressure, presence of edema, orthostatic vital signs 1, 2
- Blood pressure measurement - both lying and standing 1
- Skin examination - for rashes suggesting systemic illness (vasculitis, drug reactions) 3
- Cardiac examination - for pericardial friction rub (uremic pericarditis) 3
Context-Dependent Presentations
Prerenal AKI
Patients typically present with clear precipitants 2:
- Recent history of severe vomiting, diarrhea, or bleeding 2
- Rapid creatinine rise with preserved baseline function 2
- Clinical dehydration signs 2
Patients with Pre-existing Conditions
Diabetes and hypertension increase AKI risk and may mask early symptoms 2, 8. Patients on ACE inhibitors, ARBs, or diuretics may develop AKI more readily during volume depletion 2, 8.
Elderly patients (>65 years) are at higher risk and may present atypically 8.
Pre-existing CKD patients may have AKI superimposed on chronic disease, making detection more challenging 1.
Critical Pitfalls
The absence of symptoms does not exclude AKI - this is the most important clinical caveat 5. Many cases are detected only through laboratory monitoring in hospitalized patients or those with risk factors 5, 3.
Urine output may be preserved - non-oliguric AKI is common and does not indicate less severe disease 3, 7.
Baseline creatinine may be unknown - making the diagnosis more difficult, particularly in community settings 1. In such cases, a presumed baseline may need to be estimated 1.
Specific Populations
Neonates
Present unique challenges 1:
- High urine output AKI is common and may go unrecognized 1
- Serum creatinine initially reflects maternal levels 1
- Low baseline GFR is physiologic in this population 1