Does erythrocytosis (increased red blood cell mass) affect Glomerular Filtration Rate (GFR)?

Impact of Erythrocytosis on Glomerular Filtration Rate

Erythrocytosis negatively impacts glomerular filtration rate (GFR) primarily through increased blood viscosity, which reduces renal blood flow and can lead to glomerular abnormalities and eventual sclerosis. 1

Pathophysiological Mechanisms

• Erythrocytosis (increased red blood cell mass) exponentially increases blood viscosity, which directly affects renal hemodynamics and microcirculation 1
• In chronic cyanotic conditions with erythrocytosis, renal glomeruli become abnormal, hypercellular, and congested, eventually progressing to sclerosis 1
• The increased viscosity from erythrocytosis decreases blood flow in small capillaries, including those in the kidney, impairing tissue perfusion 1
• Erythrocytosis can lead to reduced glomerular filtration rate, increased creatinine levels, and proteinuria 1

Hemodynamic Effects

• Blood viscosity increases exponentially with rising hematocrit levels, particularly affecting microcirculatory blood flow 2
• Erythrocytosis affects rheological properties of blood, which can compromise renal perfusion and filtration 1
• Increased red cell mass causes increased blood viscosity, which becomes a limiting factor in oxygen delivery to tissues, including the kidneys 1
• Paradoxically, severe erythrocytosis does not stimulate further erythropoietin production because decreased renal blood flow is matched by decreased oxygen consumption for sodium reabsorption, maintaining tissue oxygen tension 3

Clinical Implications

• Patients with erythrocytosis require proper hydration before procedures involving contrast media due to their already compromised renal function 1
• Medications affecting renal function (ACE inhibitors, diuretics, NSAIDs, select antibiotics) should be used cautiously in patients with erythrocytosis 1
• Therapeutic phlebotomy should be considered only when hemoglobin exceeds 20 g/dL and hematocrit is greater than 65% with associated symptoms of hyperviscosity 1
• Repeated routine phlebotomies are not recommended due to the risk of iron depletion, which can lead to microcytic red cells with reduced deformability, potentially worsening microcirculation 1

Specific Renal Manifestations

• Abnormal urate clearance is common in erythrocytosis, which combined with increased red blood cell turnover leads to hyperuricemia 1
• Chronic cyanosis with erythrocytosis can lead to proteinuria due to glomerular damage 1
• The relationship between hematocrit and renal function is bidirectional - while renal insufficiency typically causes anemia, erythrocytosis can impair renal function 4
• Erythrocytosis can unmask underlying renal conditions or exacerbate existing kidney disease 5

Monitoring and Management

• Regular assessment of renal function is essential in patients with erythrocytosis 1
• Maintaining proper hydration is critical to mitigate the negative effects of increased blood viscosity on renal function 1
• When therapeutic phlebotomy is necessary, equal volume replacement with dextrose or saline is essential to prevent further compromise of renal perfusion 1
• Addressing underlying causes of erythrocytosis (such as chronic hypoxemia) may help prevent progressive renal damage 1, 5

In conclusion, erythrocytosis has significant negative effects on GFR through multiple mechanisms, primarily related to increased blood viscosity and altered renal hemodynamics, requiring careful monitoring and management to preserve renal function.