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28: Kidney Injury, Acute

CHIEF COMPLAINT

PATIENT image

Mr. T is 77-year-old man with acute kidney injury (AKI).

image What is the differential diagnosis of AKI? How would you frame the differential?

CONSTRUCTING A DIFFERENTIAL DIAGNOSIS

AKI is a syndrome defined as a reduction in kidney function that has occurred within the last 7 days. AKI can occur in patients with no known kidney disease but is more likely to develop in patients with preexisting kidney disease. Table 28-1 summarizes the current diagnostic criteria and staging for AKI, and acute and chronic kidney disease (CKD).

Table 28-1.Diagnostic criteria and staging for kidney disease.
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Table 28-1. Diagnostic criteria and staging for kidney disease.
Staging
Syndrome Serum Creatinine (Scr)/GFR Criteria Evidence of Kidney Damage1 Stage2 Scr Urinary Output
Acute kidney injury (AKI)

• Increase in serum creatinine by ≥ 0.3 mg/dL within 48 hours or

• Increase to ≥ 1.5 times baseline within 7 days or

• Urine volume < 0.5 mL/kg/h for 6 hours

 Not required for diagnosis

1

2

3

↑ by ≥ 0.3 or 1.5–1.9 times baseline

2–2.9 times baseline

3 times baseline or ≥ 4 mg/dL or dialysis

< 0.5 mL/kg/h for 6–12 hours

< 0.5 mL/kg/h for ≥ 12 hours

< 0.3 mL/kg/h for ≥ 24 hours or anuria
Acute kidney disease (AKD)3

• AKI or

• GFR < 60 mL/min for < 3 months or

• Decrease in GFR by ≥ 35% or increase in serum creatinine > 1.5 times baseline for < 3 months

 Present for < 3 months No staging
Chronic kidney disease (CKD)3 GFR < 60 mL/min for > 3 months Present for > 3 months GFR stages Albuminuria stages (ACR)

G1 > 90

G2 60–89

G3a 45–59

G3b 30–44

G4 15–29

G5 < 15

A1 < 30 mcg/mg

A2 30–299 mcg/mg

A3 ≥ 300 mcg/mg

1 Kidney damage is defined as any of the following: urinalysis with casts (red cell, white cell, renal tubular epithelial, or granular), proteinuria [albumin/creatinine ratio (ACR) > 30 mg/g or protein/creatinine ratio (PCR) > 150 mg/g], abnormal histology, abnormalities on imaging (size abnormalities, hydronephrosis, cysts, stones), or presence of a transplanted kidney.

2 Patients should be assigned the higher stage when Scr and urinary output criteria are discordant.

3 Patients have AKD or CKD if they meet either the creatinine/GFR criteria or have evidence of kidney damage.

GFR, glomerular filtration rate.

The framework for the differential diagnosis of AKI is a combination of anatomic and pathophysiologic:

  1. Prerenal (due to renal hypoperfusion)

    1. Hypovolemia

      1. Gastrointestinal fluid loss

      2. Renal loss

      3. Hemorrhage

      4. Third spacing

    2. Decreased effective circulating volume (with or without hypotension)

      1. Heart failure (HF)

      2. Cirrhosis

    3. Hypotension

      1. Sepsis

      2. Cardiogenic shock

      3. Anaphylaxis

      4. Anesthesia- and medication-induced

      5. Relative hypotension below patient’s autoregulatory level

    4. Changes in renal hemodynamics

      1. Nonsteroidal antiinflammatory drugs (NSAIDs) (including cyclooxygenase (COX)-2 inhibitors)

      2. Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers

      3. Renal artery thrombosis or embolism

      4. Abdominal aortic ...

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