Top Concerns with One-Time Increase in Hemoglobin and Hematocrit
A one-time increase in hemoglobin (Hb) and hematocrit (Hct) should raise immediate concerns about increased blood viscosity, which can lead to thrombotic events, cardiovascular complications, and potential mortality.
Primary Concerns
Cardiovascular Risks
- Increased blood viscosity from elevated Hb/Hct creates higher resistance to blood flow, potentially leading to hypertension, decreased tissue perfusion, and increased cardiac workload 1
- A 20% increase in blood viscosity can decrease blood flow rate by approximately 16.67% and may require a 20% increase in blood pressure to maintain circulation 1
- Elevated blood viscosity and Hct are significantly associated with increased risk of cardiovascular events including ischemic heart disease and stroke 2
Thrombotic Complications
- Red blood cell transfusions and resulting rapid increases in Hb/Hct have been associated with increased risks of venous thromboembolism (odds ratio 1.60) and arterial thromboembolism (odds ratio 1.53) 3
- Higher Hb/Hct values increase blood viscosity in an exponential fashion, particularly when Hct exceeds 54%, significantly altering pulmonary hemodynamics 4
- Increased blood viscosity may promote ischemic heart disease and stroke through altered rheological properties 2
Pulmonary Vascular Effects
- Pulmonary vascular resistance rises exponentially as Hct increases, particularly when pulmonary blood flow is less than normal 4
- This increased resistance can lead to pulmonary hypertension and may contribute to the development of pulmonary arteriosclerosis in susceptible patients 4
Metabolic Consequences
- Elevated blood viscosity and Hct are associated with insulin resistance and are independent risk factors for developing type 2 diabetes mellitus 5
- Adults in the highest quartile of blood viscosity have a 68% higher risk of developing diabetes compared to those in the lowest quartile 5
Clinical Approach to Evaluating a One-Time Increase
Differentiate True from Apparent Polycythemia
- Determine if the elevation represents true polycythemia (actual increase in red cell mass) or apparent polycythemia (decreased plasma volume) 3
- Consider common causes of relative polycythemia such as dehydration, diuretic use, vomiting, diarrhea, or burns 3
Evaluate for Underlying Causes
- For true polycythemia, distinguish between primary polycythemia vera (clonal disorder) and secondary polycythemia (often EPO-mediated) 3
- Secondary causes include hypoxia-driven conditions (high altitude, pulmonary disease, sleep apnea) or hypoxia-independent conditions (renal tumors, other malignancies) 3
Monitoring Recommendations
- Repeated Hb/Hct measurements are essential as initial values in the normal range may mask early-phase bleeding 3
- If the increase in Hct exceeds 8 percentage points per month (or Hb increase >3 g/dL per month), consider reducing EPO dosing by 25% if the patient is on such therapy 3
Management Considerations
Transfusion-Related Concerns
- If the increase is due to transfusion, be aware that RBC transfusions have been associated with increased mortality (odds ratio 1.34), particularly with units stored for more than 14 days 3
- The major benefit of transfusion is rapid increase in Hb/Hct levels, with 1 unit of PRBCs typically increasing Hb by 1 g/dL or Hct by 3% 3
Thrombosis Prevention
- For patients with significantly elevated Hb/Hct, consider prophylactic measures against thrombosis, particularly in those with additional risk factors 2
- Monitor for signs of cardiovascular or cerebrovascular compromise, especially in patients with pre-existing disease 3
Addressing Underlying Causes
- If secondary polycythemia is identified, treat the underlying cause (e.g., CPAP for sleep apnea, smoking cessation for smoker's polycythemia) 3
- For primary polycythemia, hematology consultation is warranted for consideration of cytoreductive therapy 3
Special Populations
Patients with Traumatic Brain Injury
- Despite traditional practice of maintaining higher Hb levels (approximately 10 g/dL) in TBI patients, evidence suggests this approach does not improve outcomes 3
- RBC transfusions in TBI patients have been associated with two-fold increased mortality and three-fold increased complication rates 3
- Increasing Hct above 28% during the initial unstable phase following severe TBI has not been associated with improved outcomes 3