What is the impact of phlebotomy on hemoglobin (Hb) levels?

From the Guidelines

Phlebotomy has a significant impact on hemoglobin (Hb) levels, with frequent blood draws contributing to the development of anemia in patients, particularly in intensive care unit (ICU) settings.

Key Findings

• Adult ICU patients lose approximately 340–660 mL of blood per week to diagnostic testing, with an 18% increase in the risk of anemia for each 50 mL of blood lost 1.
• The use of small volume tubes and closed blood sampling devices can reduce blood loss, with bundled interventions resulting in a 65% reduction in blood loss among adult ICU patients 1.
• Mathematical modeling suggests that it would take 40–70 days of 53 mL/day of blood loss for adults with normal body weight and hemoglobin at admission to the ICU to become anemic, but patients with reduced erythropoiesis and low body weight may develop anemia more quickly 1.
• Interventions to minimize phlebotomy blood loss, such as non-invasive testing and point of care testing, can help prevent iatrogenic anemia 1.

Hemoglobin Levels

• The decline in hemoglobin levels due to phlebotomy can be significant, with one study finding that the hemoglobin concentrations of patients with reduced erythropoiesis and low body weight may decline to 70 g/L or less by 9–14 days 1.
• Bundled interventions have been shown to improve hemoglobin decline in some studies, but the evidence is inconsistent 1.

Clinical Implications

• The prevention of iatrogenic anemia is crucial, as it can reduce the need for transfusions and associated risks, such as infection and transfusion reaction 1.
• Healthcare providers should consider implementing interventions to minimize phlebotomy blood loss, such as using small volume tubes and closed blood sampling devices, and promoting non-invasive testing and point of care testing 1.

From the Research

Impact of Phlebotomy on Hemoglobin Levels

• Phlebotomy has been shown to have a significant impact on hemoglobin (Hb) levels in patients, particularly in critically ill patients 2, 3, 4.
• Studies have found that the blood volume drawn and number of phlebotomies performed are correlated with decreases in Hb levels 2.
• A study found that 59.7% of patients experienced a mild decrease in Hb levels (< 2g/dl), while 21.8% presented a more severe reduction (> 2g/dl) 2.
• The frequency and volume of laboratory draws have been found to differ across ICU types, with the greatest frequency of laboratory draws in the cardiac surgical ICU and the greatest daily phlebotomy volume in the medical ICU 3.

Factors Influencing Hemoglobin Measurements

• The blood draw site and analytical device used can have a small but statistically significant effect on Hb measurements 5.
• A study found that the mean Hb content was 0.32-0.47 g/dL (2-4%) higher in capillary compared to venous blood from the same donors 5.
• The use of different Hb measuring instruments can also result in variations in Hb measurements, with some devices producing higher mean Hb content compared to others 5.

Relationship Between Phlebotomy and Anemia

• Phlebotomy-associated blood loss is a potentially modifiable contributor to anemia in critically ill patients 4.
• A study found that cumulative blood loss due to laboratory testing was independently associated with red blood cell (RBC) transfusion 4.
• Patients in the highest quartile of cumulative blood drawn experienced the longest hospitalizations, lowest nadir Hb concentrations, and greatest RBC transfusion utilization 3.
• Estimated annual phlebotomy costs exceeded $15 million, highlighting the significant economic burden of phlebotomy-associated blood loss 3.