Chronic Kidney Disease

Clinical Relevance and Diagnostic Emphasis for FNPs

Chronic kidney disease (CKD) is a progressive loss of kidney function over months to years, affecting approximately 15% of US adults.^[1] As an FNP, you will frequently encounter CKD in primary care settings, often before the patient reaches nephrology. Early recognition and management can slow progression, reduce cardiovascular risk, and delay the need for dialysis. On exams, expect questions on staging (based on GFR and albuminuria), common complications (anemia, mineral bone disorder, metabolic acidosis), and pharmacologic considerations (e.g., dosing adjustments, nephrotoxic avoidance).

Essential Parameters: eGFR, Albuminuria, and Staging

• Glomerular Filtration Rate (GFR): Best overall index of kidney function. Normal is >90 mL/min/1.73 m². Estimated GFR (eGFR) is calculated using serum creatinine, age, sex, and race (the 2021 CKD-EPI equation without race is now recommended).^[2]
• Albuminuria: Abnormal urinary albumin excretion. Measured as UACR (urine albumin-to-creatinine ratio). ≥30 mg/g indicates kidney damage.
• CKD Staging (KDIGO 2024): Combines GFR category (G1–G5) and albuminuria category (A1–A3) to assign risk.^[3]
• Kidney failure (ESKD): eGFR <15 mL/min/1.73 m², or need for dialysis/transplant.
• Nephron: Functional unit of kidney; progressive nephron loss underlies CKD.

KDIGO Staging Criteria and Pathophysiology

Staging System (KDIGO)

Albuminuria categories: A1 (<30 mg/g), A2 (30–300 mg/g), A3 (>300 mg/g). Risk of progression increases when both GFR decline and albuminuria are present.

Pathophysiology Summary

• Initial insult (e.g., diabetes, hypertension, glomerulonephritis) causes nephron loss.
• Remaining nephrons hyperfiltrate, leading to further sclerosis.
• Declining GFR impairs excretion of waste, fluid, and electrolytes.
• Fibrosis and inflammation amplify damage via cytokines (TGF-β).

Recognizing Early and Late Manifestations

Early CKD is often asymptomatic. Symptoms typically appear in G4–G5.

• Early (G1–G3): Usually none; may have mild fatigue, nocturia, or hypertension.
• Late (G4–G5):
  • Volume overload: edema (peripheral, periorbital), dyspnea, hypertension.
  • Uremic symptoms: anorexia, nausea, pruritus, metallic taste, restless legs.
  • Electrolyte abnormalities: hyperkalemia, metabolic acidosis.
  • Anemia: due to ↓ erythropoietin; fatigue, pallor, dyspnea on exertion.
  • Mineral bone disorder: hypocalcemia, hyperphosphatemia, secondary hyperparathyroidism → bone pain, fractures.

Diagnostic Algorithms and Referral Guidelines

1. Confirm diagnosis: eGFR <60 for ≥3 months, OR evidence of kidney damage (albuminuria, abnormal sediment, imaging).^[3]
2. Assess cause: Diabetes (most common), hypertension, glomerulonephritis, polycystic kidney disease, autoimmune (e.g., lupus).
3. Staging labs: Serum creatinine, eGFR (CKD-EPI 2021), UACR, BMP (including calcium, phosphate), CBC, PTH, and vitamin D levels.
4. Renal ultrasound: Evaluate for hydronephrosis, cysts, kidney size (small kidneys suggest chronicity).
5. Referral indicators: eGFR <30, rapid decline, UACR >300 mg/g, uncontrolled hypertension, or diagnostic uncertainty. Recommend nephrology consult at G4.^[4]

Pharmacologic and Lifestyle Interventions to Slow Progression

General Management Strategy

• Blood pressure control: Target <130/80 mm Hg. First-line: ACE inhibitors or ARBs, especially if albuminuria present. These reduce proteinuria and slow progression.^[5]
• Glycemic control in diabetes: Target HbA1c 7–8% (avoid hypoglycemia, which is riskier with reduced kidney clearance). Metformin requires dose adjustment and is contraindicated when eGFR <30.
• SGLT2 inhibitors: (e.g., dapagliflozin, empagliflozin) reduce CKD progression and heart failure events in patients with eGFR ≥25 and albuminuria. Now first-line adjunct after ACEi/ARB.^[5]
• Dietary modifications: Limit sodium (<2 g/day), moderate protein (0.8 g/kg/day in non-dialysis CKD), and restrict potassium/phosphate as levels dictate.
• Anemia management: Iron supplementation (oral or IV) plus erythropoiesis-stimulating agents (ESA) if Hb <10 g/dL after iron repletion. Target Hb ~10–11.5 g/dL.
• Mineral bone disorder: Phosphate binders (e.g., calcium acetate, sevelamer), vitamin D analogs (e.g., calcitriol), cinacalcet for secondary hyperparathyroidism.
• Acidosis: Oral sodium bicarbonate or citrate if serum bicarbonate <22 mEq/L to slow progression.
• Avoid nephrotoxins: NSAIDs, contrast dye (if possible; pre-hydrate if needed), and certain antibiotics (aminoglycosides, vancomycin) with careful dosing.

Avoiding Adverse Events and Managing Comorbidities

• Hyperkalemia: Risk increases with GFR <30, use of ACEi/ARB, potassium-sparing diuretics, or NSAIDs. Monitor K+ closely; treat with dietary restriction, loop diuretics, or patiromer if persistent.
• Medication dosing errors: Many drugs require dose adjustment as eGFR declines. Check each prescription before ordering.
• Fluid overload: Common in G4–G5; use loop diuretics (furosemide, torsemide) cautiously. Avoid thiazides alone if eGFR <30 (ineffective).
• Contrast-induced nephropathy: Risk is elevated in CKD. Use lowest possible contrast volume, pre-hydrate with isotonic fluids, and avoid if eGFR <30 unless absolutely necessary.
• Cardiovascular disease: Leading cause of death in CKD. Manage CV risk aggressively: statins (atorvastatin recommended in CKD), antiplatelets when indicated.

Exam-Focused Reminders and Clinical Shortcuts

• Staging is high yield: Know the eGFR cutoffs and how albuminuria modifies risk. A G3aA2 patient is higher risk than G3aA1.
• ACEi/ARB + SGLT2i double therapy is now standard for proteinuric CKD regardless of diabetes status. Memorize: "ACEi/ARB first, then add SGLT2i if eGFR ≥25."
• Screen all CKD patients for anemia (CBC) and mineral bone disorder (Ca, Phos, PTH) starting at G3b.
• Metformin + CKD: Stop metformin if eGFR <30. For eGFR 30–45, max dose 1000 mg/day.
• Contrast precautions: Withhold metformin 48h before contrast if eGFR <60, and restart after 48h if renal function stable.
• Referral timing: FNP should refer to nephrology for eGFR <30, rapid decline (>5 mL/min/yr), UACR >300, or difficult BP control.
• Memory aid for uremic symptoms: "NUMP" – Nausea, uremic frost (rare), metallic taste, pruritus.
• Vitamin D in CKD: Use active forms (calcitriol, paricalcitol) not cholecalciferol once eGFR <30 because failing kidneys cannot hydroxylate 25-OH to 1,25-(OH)₂D.

References & Sources

1. Centers for Disease Control and Prevention. Chronic Kidney Disease in the United States, 2023. https://www.cdc.gov/kidneydisease/publications-resources/ckd-national-facts.html
2. Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C–based equations to estimate GFR without race. N Engl J Med. 2021;385:1737–1749. https://doi.org/10.1056/NEJMoa2102953
3. 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):S1–S117. https://kdigo.org/guidelines/ckd-evaluation-and-management/
4. National Kidney Foundation. KDOQI clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Am J Kidney Dis. 2002;39(2 Suppl 1):S1–S266. https://www.kidney.org/professionals/guidelines
5. Kidney Disease: Improving Global Outcomes (KDIGO) Blood Pressure Work Group. KDIGO 2021 clinical practice guideline for the management of blood pressure in chronic kidney disease. Kidney Int. 2021;99(3S):S1–S87. https://kdigo.org/guidelines/blood-pressure-in-ckd/