Drawing Too Much Blood May Increase Anemia Risks

Reed Miller

August 11, 2011

August 11, 2011 (Kansas City, Missouri) — Taking less blood from acute-MI patients for diagnostic tests may improve patient outcomes by reducing the risk of hospital-acquired anemia, a new study published online August 8, 2011 in the Archives of Internal Medicine suggests [1].

Multiple studies have shown that hospital-acquired anemia is associated with greater mortality and worse health status in patients with acute MI, but the relationship between diagnostic phlebotomy and the risk of hospital-acquired anemia had not been rigorously studied in this population, according to Dr Adam Salisbury (Saint Luke’s Mid-America Heart and Vascular Institute, Kansas City, MO) and colleagues.

Salisbury and colleagues analyzed records from 57 centers from in the Cerner Health Facts electronic medical records database. This database was ideal for studying the link between phlebotomy and hospital-acquired anemia because it contains detailed information on patients' laboratory tests and patients' hemoglobin levels across a variety of hospitals. The database included 17 676 acute-MI patients who were not anemic at admission. Each patient's total diagnostic blood loss was estimated based on the standard volume for each tube type used to draw blood in that patient.

In the study, moderate to severe hospital-acquired anemia--a hemoglobin level decline from normal to <11 g/dL--was found in 3551 patients (20%). The mean volume of blood taken for diagnostics was higher in patients with anemia (173.8 mL) than in those who did not develop anemia (83.5 mL) (p<0.001). For every 50 mL of blood drawn, a patient's risk of developing moderate to severe hospital-acquired anemia increased by18%. The risk was only slightly attenuated after multivariable adjustment.

The average blood loss per patient varied significantly among hospitals, from 53.0 mL to 109.6 mL for the entire cohort. The interhospital variability was even greater among patients with moderate to severe anemia, from 119.1 mL to 246.0 mL, and the study showed that incidences of moderate to severe anemia were more frequent at hospitals with higher average diagnostic blood loss.

The average blood loss for patients developing hospital-acquired anemia was about half a standard unit of whole blood, and more than 12% of these patients had more than 300 mL of blood drawn over the course of hospitalization, with patients staying longer at the hospital tending to lose more blood to diagnostics. "Since most diagnostic evaluation and therapeutic interventions often occur early during AMI hospitalization, it is likely that much of the blood taken later during hospitalization represents routine, scheduled laboratory draws that could lead to ongoing blood loss," Salisbury et al explain.

The findings indicate that reducing blood loss from phlebotomy could limit the development and severity of hospital-acquired anemia. This could be accomplished inexpensively by using smaller blood tubes, such as those made for pediatric patients, filling standard tubes with less blood, relying more on stored serum samples, or simply reducing unnecessary, scheduled blood tests, according to the authors. But they also point out that blood loss to diagnostics is not the only cause of hospital-acquired anemia, so these blood-draw-reduction efforts must be part of a multimodal effort to reduce bleeding.

The authors also point out that because this study was retrospective, new randomized trials will be needed to test the hypothesis that reducing phlebotomy prevents hospital-acquired anemia and improves patients’ outcomes.

The study was partly supported by the American Heart Association–Pharmaceutical Roundtable and David and Stevie Spina. Salisbury had no disclosures. Disclosures for the coauthors are listed in the paper.


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