Is this a case of AKI (Acute Kidney Injury) or CKD (Chronic Kidney Disease) given elevated urea and creatinine levels without a baseline renal profile?

Distinguishing AKI from CKD Without Baseline Renal Profile

Without a baseline creatinine, you should presume this is Acute Kidney Disease (AKD) and manage it as such, while simultaneously investigating for features of chronicity through imaging, urinalysis, and clinical history. 1

Initial Diagnostic Approach

Estimate a baseline creatinine using back-calculation from an assumed eGFR of 75 ml/min/1.73 m² to determine if AKI criteria are met. 1 This approach is most accurate in younger patients with likely preserved kidney function, though it may overestimate AKI severity if unrecognized CKD risk factors exist. 1

For a 45-year-old woman with creatinine 190 µmol/L (approximately 2.15 mg/dL):

• This level represents significant renal dysfunction regardless of whether it's acute or chronic. 1
• Using known creatinine values is always superior to imputation when available, so aggressively search for any prior laboratory data. 1

Clinical Features to Distinguish AKI from CKD

Favor AKI/AKD if present:

• Recent acute illness, sepsis, hypotension, or nephrotoxin exposure within the past 7-90 days 1
• Symptoms of uremia developing over days to weeks 2
• Normal to enlarged kidney size on ultrasound (>10 cm in adults) with preserved parenchymal thickness 3
• Normal to mildly increased echogenicity on renal ultrasound 3

Favor CKD if present:

• Small kidneys (<9 cm) with reduced cortical thickness on ultrasound 3
• Markedly increased echogenicity with small echogenic kidneys 3
• Anemia, hyperparathyroidism, or metabolic bone disease 1
• Long-standing hypertension, diabetes, or proteinuria documented previously 1

Important caveat: Infiltrative diseases, diabetic nephropathy, and HIV nephropathy can cause CKD with normal or enlarged kidneys, potentially mimicking AKI. 3

The Concept of Acute Kidney Disease (AKD)

AKD describes kidney dysfunction persisting between 7 and 90 days after an AKI-initiating event, and this is likely what you're encountering without baseline data. 1

• If dysfunction persists beyond 90 days, it transitions to CKD by definition. 1
• AKD can occur without meeting strict AKI criteria if the creatinine rise was gradual rather than abrupt. 1, 4
• Even when creatinine appears to normalize, subclinical injury and loss of renal reserve frequently persist. 5, 6

Practical Management Algorithm

Immediate Actions:

1. Order renal ultrasound to assess kidney size, echogenicity, and exclude obstruction 3
2. Obtain urinalysis looking for proteinuria, hematuria, or cellular casts 1
3. Review medication list and discontinue all nephrotoxins immediately 1, 5
4. Assess volume status and optimize hemodynamics 1
5. Search exhaustively for any prior creatinine values in medical records, other facilities, or outpatient laboratories 1

Diagnostic Workup:

• Check hemoglobin, calcium, phosphate, and parathyroid hormone to assess for chronicity 1
• Measure urine protein-to-creatinine ratio 1
• Consider cystatin C measurement, as it may reveal dysfunction missed by creatinine alone 7
• Serial creatinine measurements over 48-72 hours to determine trajectory 1, 6

Follow-up Strategy:

• Plan nephrology follow-up within 7-14 days regardless of presumed diagnosis 1, 5
• Monitor kidney function for at least 90 days to distinguish AKD from CKD progression 1, 5
• Don't assume recovery is complete if creatinine improves—loss of renal reserve and ongoing subclinical injury may persist 5, 6

Critical Pitfalls to Avoid

Don't rely solely on discharge creatinine to assess renal function after critical illness, as muscle wasting can cause falsely reassuring creatinine levels. 6 In one study, creatinine decreased by 33% from admission to discharge in patients without AKI due to loss of muscle mass, potentially masking persistent renal dysfunction. 6

Don't use standard eGFR equations designed for CKD to assess kidney function during the acute or subacute phase—they are inaccurate in this setting. 5

Don't discharge without a clear follow-up plan, as the 7-90 day window is critical for preventing progression to CKD. 1, 5, 4

Recognize that AKI and CKD frequently coexist (acute-on-chronic kidney disease), making pure categorization impossible in many cases. 1, 8, 4 This patient may have both, and management should address both possibilities until proven otherwise.