Acute Kidney Injury vs Chronic Kidney Disease

Medical-Surgical · Renal & Genitourinary·Updated 2026-10-28

What it is

Acute kidney injury (AKI) is a rapid loss of kidney function over hours to days, shown by a rising serum creatinine or falling urine output, and it is often reversible if the cause is corrected. Chronic kidney disease (CKD) is kidney damage or a GFR below 60 mL/min/1.73 m2 for more than 3 months, most often from diabetes and hypertension, and it is progressive and irreversible. In both, the kidneys cannot excrete fluid, potassium, phosphate, acid and urea, so care centers on fluid balance, electrolytes and protecting the remaining nephrons.

What the NCLEX focuses on

Prerenal AKI (most common): hypovolemia, hypotension or heart failure reduce renal blood flow; the kidneys conserve sodium and water, so urine is concentrated, urine sodium is low, and output improves with fluid.
Intrarenal AKI: acute tubular necrosis from prolonged ischemia or nephrotoxins (aminoglycosides, iodinated contrast, NSAIDs). Postrenal AKI: outflow obstruction from an enlarged prostate, stones or tumor.
AKI phases: oliguric (below 400 mL/day; fluid overload, hyperkalemia, metabolic acidosis), diuretic (up to 3 to 5 L/day; hypovolemia, hypokalemia, hyponatremia), then recovery over up to 12 months.
In the oliguric phase, fluid intake is limited to the previous 24-hour output plus 600 mL.
CKD stages by GFR: stage 3 is 30 to 59, stage 4 is 15 to 29 (plan for dialysis or transplant), stage 5 is below 15 (kidney failure).
CKD effects: anemia from low erythropoietin; high phosphorus, low calcium and bone disease; hypertension; uremic pruritus; pericarditis (friction rub); hyperkalemia and metabolic acidosis.
CKD drugs: ACE inhibitor or ARB to slow progression; phosphate binders with meals; hold an erythropoiesis-stimulating agent and report when hemoglobin rises above 11 g/dL (110 g/L).

Priority nursing actions

Find and remove the cause: restore volume in prerenal AKI, bladder scan and catheterize for obstruction, and question nephrotoxic drugs.
Monitor hourly urine output, daily weight, lung sounds and edema.
Monitor potassium, cardiac rhythm, BUN, creatinine and ABG.
Limit fluid, sodium, potassium and phosphorus as prescribed while maintaining adequate calories.
Prepare for dialysis when hyperkalemia, fluid overload, acidosis or uremic signs do not respond to treatment.

Numbers to know

Value	Normal or target	Why it matters
Serum creatinine	0.6 to 1.2 mg/dL (53 to 106 micromol/L)	AKI: rise of 0.3 mg/dL in 48 hours or 1.5 times baseline
BUN	10 to 20 mg/dL (3.6 to 7.1 mmol/L)	Also rises with dehydration and GI bleeding; less specific than creatinine
Urine output	At least 0.5 mL/kg/h	Below this for 6 hours meets AKI criteria
Oliguria	Less than 400 mL in 24 hours	Defines the oliguric phase
Oliguric fluid allowance	Previous 24-hour output plus 600 mL	Replaces insensible loss without overload
GFR	90 mL/min/1.73 m2 or higher	Below 60 for 3 months means CKD; below 15 means kidney failure

Common exam traps

Choosing continuous 0.9% sodium chloride at 125 mL/h for an oliguric client: wrong because it causes fluid overload and pulmonary edema.
Choosing intake and output totals over daily weight to judge fluid status: wrong because daily weight is the most accurate measure.
Choosing a high BUN alone as proof of kidney damage: wrong because creatinine is more specific; BUN rises with dehydration.
Choosing to relax monitoring when urine output rises to 4 L a day: wrong because the diuretic phase causes hypovolemia and hypokalemia.
Choosing magnesium hydroxide or a phosphate enema for a client with CKD: wrong because magnesium and phosphate accumulate.

What to teach

Limit sodium, high-potassium foods (bananas, oranges, potatoes, tomatoes) and high-phosphorus foods (dairy, colas, processed meats); take phosphate binders with meals.
Weigh daily and report rapid gain, swelling or shortness of breath.
Avoid NSAIDs, salt substitutes and herbal products, and tell every provider about kidney disease before contrast studies.
Protect the veins of one arm for future dialysis access: no blood draws or IV lines in that arm.

Client handout: Chronic Kidney Disease: Food and Fluids (nurse guide and printable patient handout).

Try 2 NCLEX-style questions on this topic

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Question 1 · QID 0567D53C

A client in the oliguric phase of AKI has a urine output of 350 mL over 24 hours. Which prescription should the nurse question?

A. Restrict oral and IV fluids to the urine output plus 600 mL per day
B. Infuse 0.9% sodium chloride at 125 mL/hr continuously
C. Limit dietary potassium
D. Daily weight before breakfast

Question 2 · QID FCAA06B4

The nurse reviews food choices with a client who has stage 4 CKD on potassium, phosphorus, and sodium restriction. Which foods should the client avoid? Select all that apply.

A. Processed deli meats
B. Bananas and orange juice
C. Cola beverages
D. White rice
E. Dairy products in large amounts
F. Applesauce

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More tips on Medical-Surgical

Acute PancreatitisRecognize acute pancreatitis by pain and lipase, give fluids and pain control first, and catch hypocalcemia, shock and respiratory failure.Bowel Obstruction and NG Tube CareTell small from large bowel obstruction, spot strangulation early, and keep a decompression NG tube placed, patent and safe.Hyperkalemia: ECG Changes and Treatment OrderRecognize hyperkalemia on the ECG and treat it in the right order: protect the heart, shift potassium into cells, then remove it.

Sources

Harding MM, Kwong J, Hagler D, Reinisch C. Lewis's Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 12th ed. Elsevier; 2023; Chapter: Acute Kidney Injury and Chronic Kidney Disease.
Kidney Disease: Improving Global Outcomes (KDIGO) Acute Kidney Injury Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl. 2012;2(1):1-138.
Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314.

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