CKD, AKI, and Stages of Kidney Disease
Key Takeaways
- KDIGO defines CKD as abnormalities of kidney structure or function present for ≥3 months, staged by GFR (G1–G5) and albuminuria (A1–A3).
- AKI is a sudden decrease in kidney function over hours to days; KDIGO stages AKI by creatinine rise and urine output.
- Prerenal AKI reflects hypoperfusion; intrinsic renal injury involves parenchymal damage; postrenal AKI results from urinary obstruction.
- ESRD (G5) typically requires renal replacement therapy when GFR is persistently below 15 mL/min/1.73 m² with uremic symptoms.
- Diabetes and hypertension are the leading CKD causes in the United States; both accelerate progression when blood pressure and glycemia are uncontrolled.
CKD, AKI, and Stages of Kidney Disease
Quick Answer: Chronic kidney disease (CKD) is kidney damage or reduced GFR <60 mL/min/1.73 m² for ≥3 months, staged G1–G5 by GFR and A1–A3 by albuminuria. Acute kidney injury (AKI) is a sudden decline in function over hours to days. ESRD (G5) usually means GFR <15 with symptoms or need for dialysis/transplant.
Dialysis nurses must translate staging language into daily decisions: when to escalate education, when to prepare access, and when AKI may recover without chronic therapy. The CDN exam tests whether you can classify disease, identify reversible AKI, and recognize progression patterns — not recite nephrology fellowship detail.
CKD Definition and Staging (KDIGO)
CKD requires either:
- Markers of kidney damage (albuminuria, hematuria, structural abnormalities, transplant history, etc.) for ≥3 months, OR
- GFR <60 mL/min/1.73 m² for ≥3 months
| GFR stage | GFR (mL/min/1.73 m²) | Plain-language meaning |
|---|---|---|
| G1 | ≥90 | Normal or high GFR with kidney damage |
| G2 | 60–89 | Mild decrease |
| G3a | 45–59 | Mild to moderate decrease |
| G3b | 30–44 | Moderate to severe decrease |
| G4 | 15–29 | Severe decrease — plan RRT education |
| G5 | <15 | Kidney failure — dialysis/transplant planning |
Albuminuria is classified separately:
| Albuminuria | UACR (mg/g) | Clinical note |
|---|---|---|
| A1 | <30 | Normal to mildly increased |
| A2 | 30–300 | Moderately increased — cardiovascular risk rises |
| A3 | >300 | Severely increased — faster CKD progression |
Report CKD as "G3bA3" — both numbers matter. A patient with GFR 38 and heavy proteinuria progresses faster than GFR 38 alone suggests.
Leading Causes and Progression
In U.S. dialysis populations, diabetes mellitus and hypertension account for most ESRD. Other causes include glomerulonephritis, polycystic kidney disease, recurrent pyelonephritis, and obstructive uropathy.
Nursing interventions that slow progression (tested conceptually on CDN):
- Blood pressure control per nephrology plan (often ACE inhibitor/ARB when tolerated)
- Glycemic management in diabetes — HbA1c individualized; avoid hypoglycemia in CKD
- Avoid nephrotoxins — NSAIDs, certain contrast exposures, aminoglycosides when alternatives exist
- Medication dose adjustment as GFR falls
AKI: Definition, Staging, and Categories
AKI is an abrupt reduction in kidney function. KDIGO staging uses serum creatinine and urine output:
| AKI stage | Creatinine | Urine output |
|---|---|---|
| 1 | 1.5–1.9× baseline OR ≥0.3 mg/dL rise | <0.5 mL/kg/h for 6–12 h |
| 2 | 2.0–2.9× baseline | <0.5 mL/kg/h for ≥12 h |
| 3 | 3× baseline OR ≥4.0 mg/dL OR RRT initiation | <0.3 mL/kg/h for ≥24 h OR anuria ≥12 h |
Etiology categories — the CDN exam loves this framework:
| Category | Mechanism | Examples | Nursing clues |
|---|---|---|---|
| Prerenal | Decreased renal perfusion | Hypovolemia, sepsis, heart failure, NSAIDs with volume depletion | BUN:Cr >20:1, FENa <1% (without diuretics), improves with volume |
| Intrinsic | Parenchymal injury | ATN (ischemic/toxic), glomerulonephritis, interstitial nephritis | Muddy brown casts (ATN), rash/eosinophilia (AIN) |
| Postrenal | Obstruction | BPH, stones, catheter kink, tumor | Sudden anuria, hydronephrosis on imaging |
Contrast-associated AKI risk rises with CKD, diabetes, hypovolemia, and high osmolar load — nursing role includes hydration protocols and holding metformin/other agents per facility policy.
CKD versus AKI on the Exam
| Feature | CKD | AKI |
|---|---|---|
| Onset | Months to years | Hours to days |
| Duration | ≥3 months | Often reversible if cause treated |
| Anemia | Gradual EPO decline | May appear rapidly in critical illness |
| Size on imaging | Often small, echogenic kidneys | Kidneys may be normal size |
| Dialysis | Planned in G5 | Urgent when life-threatening complications |
A patient with known CKD G4 who spikes creatinine after diarrhea may have AKI on CKD — not a new stage overnight without context.
Transition to ESRD and RRT Planning
ESRD generally refers to G5 requiring dialysis or transplant. Nursing milestones before first dialysis:
- Modality education — HD, PD, transplant referral
- Vascular access planning — AV fistula ideally 3–6 months before need
- PD catheter timing if PD chosen
- Dietary and medication teaching — phosphate, potassium, fluid
The "eGFR surprise" trap: eGFR equations underestimate true function in muscular patients and overestimate decline in malnourished patients — correlate with clinical picture.
Worked Exam Scenario
A 58-year-old with hypertension has eGFR 52 and UACR 180 mg/g for two annual visits. Creatinine was stable 18 months ago at eGFR 68. Which classification and priority are correct?
Answer path: Duration >3 months → CKD, not AKI. GFR 52 → G3a. UACR 180 → A2. Priority nursing focus: blood pressure control, albuminuria reduction (ACE/ARB if ordered), nephrotoxin avoidance, and RRT education is premature but advance care planning begins in G4.
Common CDN Traps
- Staging AKI and CKD with the same G1–G5 table (AKI uses separate KDIGO stages 1–3)
- Calling every G5 patient "on dialysis" — some G5 patients are conservatively managed
- Ignoring albuminuria when only GFR is listed in the stem
- Assuming dialysis cures AKI — it supports until recovery or chronic need is established
Study Routine
- Drill GFR ranges and UACR cutoffs on flashcards
- Write three stems: prerenal, ATN, obstructive — label category before reading options
- Pair each CKD stage with one nursing action (education, access planning, modality choice)
Final Check
Recite: CKD = 3+ months; G5 <15; AKI = sudden; prerenal/intrinsic/postrenal; diabetes and HTN dominate ESRD causes.
A patient has eGFR 48 mL/min/1.73 m² and UACR 250 mg/g documented on two visits 4 months apart. How should this kidney disease be classified?
A hospitalized patient develops oliguria after prolonged hypotension during sepsis. BUN 84 mg/dL, creatinine 4.2 mg/dL (baseline 1.0), urine sediment shows muddy brown granular casts. Which AKI category is most likely?
Which pair of conditions accounts for the majority of end-stage renal disease cases in the United States?