Does blood viscosity affect Glomerular Filtration Rate (GFR)?

Impact of Blood Viscosity on Glomerular Filtration Rate (GFR)

Yes, blood viscosity significantly impacts GFR, with increased blood viscosity associated with reduced renal function and elevated urinary albumin excretion in hypertensive patients. 1

Pathophysiological Mechanisms

• Blood viscosity affects renal hemodynamics by altering the pressure gradient across the glomerular filtration barrier, which directly influences GFR 2
• Increased blood viscosity reduces blood flow and elevates vascular resistance in the cardiovascular system, including the renal circulation 1
• The kidney's perfusion pressure, quantified as the difference between mean arterial pressure and central venous pressure (ideally >60 mm Hg), is critical for maintaining adequate GFR 2

Clinical Evidence

• In essential hypertensive patients without chronic kidney disease, blood viscosity correlates negatively with creatinine clearance (r=-0.185, P=0.018) and positively with urinary albumin excretion (r=0.253, P=0.001) 1
• Multiple regression analysis has identified blood viscosity as an independent determinant of both creatinine clearance and urinary albumin excretion 1

Hemodynamic Factors in Renal Function

• Hemodynamic factors are critical in determining GFR, as damage to glomeruli causes changes in the microcirculation that can result in altered filtration 2
• When kidney blood flow is reduced (due to increased viscosity or declining cardiac output), GFR can initially be preserved through compensatory increases in filtration fraction via efferent arteriolar constriction 2
• With persistent reduction in kidney perfusion, glomerular filtration decreases, driven by angiotensin II–mediated constriction of both afferent and efferent arterioles 2

Hyperfiltration and Blood Viscosity

• In conditions of altered blood viscosity, single-nephron hyperfiltration may occur as a compensatory mechanism 3
• This hyperfiltration can be "absolute" (occurring with normal nephron numbers) or "relative" (occurring when functioning nephron numbers are reduced) 3
• The biomechanical forces associated with altered blood viscosity and resulting hyperfiltration may promote progressive glomerular injury 3

Clinical Implications

• In patients with heart failure, increased venous pressure contributes to decreased arteriovenous pressure gradient, leading to reduced kidney perfusion pressure and impaired GFR 2
• Increased venous pressure is transmitted across the tubules, leading to increased intratubular pressure, which results in decreased hydrostatic pressure gradient across Bowman's capsule, reducing single-nephron GFR 2
• Patients with paraproteinemia or leukemia who have increased blood viscosity show altered cerebral blood flow patterns, suggesting similar mechanisms may affect renal blood flow 4

Management Considerations

• When GFR begins to decline substantially due to hemodynamic factors including altered blood viscosity, referral to a physician experienced in the care of such patients is indicated 2
• In patients with hyperviscosity, addressing the underlying cause should be prioritized before complications arise 5
• Monitoring renal function in patients with conditions that alter blood viscosity is essential for early detection of kidney dysfunction 1

Potential Pitfalls

• Relying solely on serum creatinine to estimate GFR in patients with altered blood viscosity may be misleading, as the relationship between creatinine and actual GFR can be affected by multiple factors 6
• Radiocontrast media are particularly nephrotoxic in patients with compromised renal function, and patients should be carefully hydrated before receiving any procedures requiring contrast that cannot be avoided 2
• Failure to recognize the impact of blood viscosity on renal function may lead to underestimation of kidney injury risk in conditions associated with hyperviscosity 1