Nephrology High-Yield: CKD, AKI, and Electrolytes for FNP Boards

Clinical High-Yield · 10 min read · April 28, 2026

Nephrology is a section that rewards systematic preparation. The boards test a specific, predictable set of renal content: CKD staging and management, the three categories of acute kidney injury, and the electrolyte disorders that require immediate recognition and treatment. Here is the high-yield content organized for maximum board efficiency.

Chronic Kidney Disease: Staging and Management

CKD is defined as kidney damage or GFR <60 mL/min/1.73m² for more than 3 months. The KDIGO staging system classifies CKD by GFR (G1–G5) and albuminuria (A1–A3). The boards test the GFR stages and the management milestones at each stage.

CKD Stages by GFR:

• G1: GFR ≥90 (normal or high GFR with evidence of kidney damage)
• G2: GFR 60–89 (mildly decreased)
• G3a: GFR 45–59 (mildly to moderately decreased)
• G3b: GFR 30–44 (moderately to severely decreased)
• G4: GFR 15–29 (severely decreased)
• G5: GFR <15 (kidney failure — dialysis or transplant)

Management milestones by stage:

• All stages: Blood pressure control (target <130/80 in CKD), ACE inhibitor or ARB for proteinuric CKD (reduces progression), dietary protein restriction (0.8 g/kg/day), sodium restriction, smoking cessation, diabetes management.
• G3b–G4: Monitor for anemia (erythropoietin deficiency — treat with ESA if Hgb <10), metabolic acidosis (treat with sodium bicarbonate if serum bicarbonate <22 mEq/L), secondary hyperparathyroidism (phosphate restriction, vitamin D supplementation), and hyperkalemia.
• G4–G5: Nephrology referral, preparation for renal replacement therapy (dialysis or transplant).

Medications to avoid or dose-adjust in CKD: The boards test this extensively. Avoid NSAIDs (reduce GFR, cause fluid retention). Avoid metformin when GFR <30 (lactic acidosis risk). Avoid direct oral anticoagulants (DOACs) at low GFR levels (varies by agent). Dose-adjust: digoxin, gabapentin, many antibiotics (aminoglycosides, vancomycin, fluoroquinolones).

Board Pearl: ACE inhibitors and ARBs are renoprotective in CKD with proteinuria — but they can cause an initial rise in creatinine (up to 30% increase is acceptable) and hyperkalemia. A creatinine rise >30% or new hyperkalemia requires dose reduction or discontinuation.

Acute Kidney Injury: The Three Categories

AKI is defined as an abrupt increase in serum creatinine ≥0.3 mg/dL within 48 hours, or ≥1.5× baseline within 7 days, or urine output <0.5 mL/kg/hour for ≥6 hours. The boards test the three categories and their distinguishing features.

Prerenal AKI: Caused by decreased renal perfusion — dehydration, hemorrhage, heart failure, sepsis, NSAIDs (reduce prostaglandin-mediated afferent arteriolar dilation). Urine findings: concentrated urine (specific gravity >1.020, osmolality >500 mOsm/kg), low urine sodium (<20 mEq/L), FENa <1%. Treatment: correct the underlying cause — IV fluids for hypovolemia, treat heart failure, discontinue nephrotoxins.

Intrinsic (intrarenal) AKI: Caused by direct kidney damage. The...