Can erythrocytosis (increased red blood cell count) cause impaired renal function (low estimated Glomerular Filtration Rate (eGFR))?

Relationship Between Erythrocytosis and eGFR

Erythrocytosis can contribute to decreased eGFR through increased blood viscosity, which impairs renal blood flow and can lead to renal dysfunction.

Pathophysiological Mechanism

Erythrocytosis (increased red blood cell count) affects kidney function through several mechanisms:

1. Increased Blood Viscosity:

   • Elevated red blood cell mass increases whole blood viscosity 1
   • Impaired blood flow can reduce renal perfusion
   • Reduced renal blood flow may lead to decreased glomerular filtration rate

2. Renal Hypoxia and Paradoxical Effects:

   • While erythrocytosis typically increases oxygen-carrying capacity, the increased viscosity can actually impair tissue oxygenation
   • In the kidneys, this creates a complex relationship where decreased blood flow might be partially offset by decreased oxygen consumption for sodium reabsorption 1

Clinical Evidence

The relationship between erythrocytosis and renal function is supported by several clinical observations:

• In chronic kidney disease (CKD), anemia is much more common than erythrocytosis, but when erythrocytosis occurs, it requires specific attention due to potential complications 2

• Erythrocytosis has been documented in various kidney conditions including:

  • Renal artery stenosis 3
  • Cystic kidney diseases
  • Post-kidney transplantation 4
  • Idiopathic membranous glomerulopathy 5

• The European Society of Cardiology notes that renal impairment is associated with multiple factors including anemia, which suggests that abnormalities in red blood cell parameters (either too few or too many) can impact kidney function 6

Monitoring and Management

When erythrocytosis is present, monitoring renal function is essential:

• Regular assessment of eGFR using CKD-EPI equation is recommended as the most accurate method for estimating GFR in adults of any age 6
• In patients with erythrocytosis, monitoring for signs of declining renal function is important, as eGFR may decrease with progression of the condition
• The National Kidney Foundation recommends monitoring serum creatinine, eGFR, electrolytes, and urine albumin-to-creatinine ratio in patients with kidney concerns 7

Clinical Implications

1. Thrombotic Risk:

   • Erythrocytosis, especially when untreated, can lead to serious thrombotic events 2
   • These thrombotic events may further compromise renal function

2. Treatment Considerations:

   • Therapeutic phlebotomy may be necessary if hemoglobin exceeds 20 g/dL and hematocrit is greater than 65% with associated symptoms of hyperviscosity 6
   • However, repeated routine phlebotomies are not recommended due to risk of iron depletion and decreased oxygen-carrying capacity 6
   • In post-transplant erythrocytosis, ACE inhibitors have been shown to be effective in normalizing hemoglobin, hematocrit, and RBC mass 4

Important Caveats

• The relationship between erythrocytosis and eGFR is bidirectional - kidney disease can cause erythrocytosis in some cases, while erythrocytosis can potentially impact kidney function
• Not all patients with erythrocytosis will develop decreased eGFR
• Other factors such as dehydration, medications, and underlying conditions may contribute to changes in eGFR in patients with erythrocytosis
• In patients with congenital heart disease and cyanosis, aggressive phlebotomy or blood loss is the most likely cause of complications rather than the erythrocytosis itself 6

In summary, while erythrocytosis can contribute to decreased eGFR through increased blood viscosity and altered renal hemodynamics, the relationship is complex and may be influenced by multiple factors. Careful monitoring of renal function is warranted in patients with erythrocytosis.