Can renal disease cause metabolic acidosis?

Renal Disease as a Cause of Metabolic Acidosis

Yes, renal disease is a significant cause of metabolic acidosis, particularly when glomerular filtration rate (GFR) falls below 60 mL/min/1.73 m² (stage 3 CKD or greater). 1

Pathophysiology of Renal-Induced Metabolic Acidosis

Metabolic acidosis in chronic kidney disease (CKD) occurs through several mechanisms:

1. Impaired acid excretion: The kidneys fail to adequately excrete acid produced by normal metabolic processes 1
2. Reduced ammoniagenesis: Damaged kidneys have decreased capacity to synthesize ammonia, which is essential for acid buffering 2
3. Bicarbonate loss: Direct loss of bicarbonate from the kidney 1
4. Reduced bicarbonate regeneration: Impaired ability to regenerate bicarbonate 3

Clinical Presentation

Metabolic acidosis in CKD typically presents with:

• Serum bicarbonate concentrations ranging from 12 to 22 mEq/L (mmol/L) 4
• Usually mild to moderate in degree 4
• Severity correlates with degree of renal impairment 4
• Can be high-anion-gap or normal anion-gap variety 4
• Becomes more prevalent when GFR falls below 20-25% of normal 4

Diagnosis

Metabolic acidosis should be suspected in patients with CKD, particularly those with:

• eGFR <60 mL/min/1.73 m² 1
• Serum bicarbonate <22 mmol/L 5
• Elevated anion gap: [Na⁺] - ([Cl⁻] + [HCO₃⁻]) >12 mEq/L 5
• Low blood pH (<7.35) 1

Adverse Effects of Metabolic Acidosis in CKD

Untreated metabolic acidosis can lead to:

• Bone demineralization and metabolic bone disease 3, 6
• Muscle wasting and protein degradation 4, 6
• Impaired growth in children 7
• Insulin resistance 4
• Accelerated progression of kidney disease 6, 2
• Increased inflammation 6
• Increased mortality 7

Management

Monitoring

• Regular monitoring of serum electrolytes and bicarbonate levels 1
• Assessment for complications of CKD (Table 11.1) when eGFR <60 mL/min/1.73 m² 1

Treatment

1. Oral sodium bicarbonate:

   • Indicated for treatment of metabolic acidosis in severe renal disease 8
   • Recommended dose: 2-4 g/day (25-50 mEq/day) divided into 2-3 doses 5
   • Target serum bicarbonate level of at least 22 mmol/L 5

2. Dietary modifications:

   • Protein intake of 0.8 g/kg body weight per day for non-dialysis CKD patients 1
   • Avoid high protein intake (>1.3 g/kg/day) as it can accelerate kidney function decline 1
   • Restriction of dietary sodium (<2,300 mg/day) 1
   • Individualization of dietary potassium 1

3. IV sodium bicarbonate:

   • Consider for severe acidosis (pH <7.2) 5
   • Used when oral therapy is not possible 5
   • Requires careful monitoring of fluid status and electrolytes 5

Complications of Treatment

• Volume overload 7
• Exacerbation of hypertension 7
• Hypokalemia 5
• Hypocalcemia 5
• Potential for vascular calcifications 7

Clinical Pearls

• Metabolic acidosis is present in the majority of patients with advanced CKD (GFR <20-25% of normal) 4
• Even mild acidosis can have substantial adverse effects on multiple organ systems 6
• Correction of acidosis with sodium bicarbonate may slow the progression of CKD 2
• The anion gap should be corrected for albumin for accurate diagnosis 5
• Metabolic acidosis is listed as a complication to screen for in patients with CKD in multiple guidelines 1

By addressing metabolic acidosis in CKD patients, clinicians can potentially improve outcomes related to bone health, muscle mass, kidney disease progression, and mortality.