Major Finding: Of patients with acute MI, 20% acquired anemia during hospitalization, and those who did so lost approximately 174 mL of blood to draws for laboratory testing, compared with only 84 mL for patients who did not develop anemia. Every 50 mL of blood drawn was associated with an 18% rise in risk for anemia.

Data Source: A retrospective, observational study of blood draws for laboratory testing and hemoglobin values in 17,676 patients hospitalized at 57 U.S. medical centers for acute MI during an 8-year period.

Disclosures: Dr. Salisbury and two associates were funded in part by an award from the American Heart Association Pharmaceutical Round Table. The investigators reported ties to numerous drug companies.

Blood loss from diagnostic blood testing during hospitalization is substantial and has been linked to anemia in patients with acute myocardial infarction, in a study of 17,676 subjects.

One in five patients developed moderate to severe hospital-acquired anemia, and they had a mean estimated phlebotomy volume of 173.8 mL – the equivalent of half a unit of whole blood. Twelve percent of the study subjects lost more than 300 mL to blood draws during the course of their hospitalization, said Dr. Adam C. Salisbury of Saint Luke's Mid America Heart and Vascular Institute, Kansas City, Mo., and his associates.

“Our findings are likely generalizable to other populations of seriously ill medical patients,” they noted.

If further research establishes that minimizing blood loss from phlebotomy prevents anemia and improves patient outcomes, there would be broad implications for all hospitalized patients. Strategies to minimize blood loss, such as using pediatric instead of adult blood tubes or filling standard 4-mL adult tubes with only 1-2 mL of blood, would be widely adopted, Dr. Salisbury and his colleagues added.

They explored the relationship between diagnostic blood testing and the risk of hospital-acquired anemia in MI patients because blood draws have been associated with increased need for transfusions in this patient population. The researchers used an electronic medical record database that detailed the frequency and type of laboratory testing as well as patients' hemoglobin levels throughout hospitalization for acute MI. The database covered 57 hospitals during a recent 8-year period.

The study cohort comprised all patients with acute MI, excluding those who already had anemia at admission and those who underwent coronary artery bypass grafting, because both the etiology and outcomes of anemia differ from those of non-CABG patients.

The data did not include exact amounts of blood drawn for every test. The investigators estimated these amounts from the types of tests that were run, assuming that only the minimal blood volume needed to run the required tests was drawn and that no blood was wasted at the blood draws.

Twenty percent of the study cohort (3,551 patients) developed moderate to severe anemia during hospitalization. Mean hemoglobin values declined in all patients, but they declined to a greater degree in those who developed anemia (−3.9 g/dL), compared with patients who didn't develop anemia (−1.6 g/dL).

“The estimated mean blood loss from phlebotomy was nearly 100 mL higher over the course of hospitalization among patients who developed moderate to severe anemia, compared with those who did not (173.8 mL vs. 83.5 mL),” the researchers said (Arch. Intern Med. 2011 Aug. 8 [doi:10.1001/archinternmed.2011.361]).

The average amount of blood drawn for laboratory testing varied significantly across hospitals, from a low of 53 mL to a high of 109.6 mL. The amount of blood typically drawn at a hospital significantly correlated with the incidence of anemia in its patients.

In a preliminary analysis, every 50 mL of blood drawn was associated with an 18% increase in the risk of hospital-acquired anemia. That risk persisted and remained robust after the data were adjusted to account for potential confounders. When the data were broken down by day of hospitalization, the risk of developing anemia was highest on the first hospital day (10.5%), then remained relatively constant at 2.8%-4.5% through 10 days of hospitalization.

“Since most diagnostic evaluation and therapeutic interventions occur early during acute MI 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.” Indeed, blood loss was particularly high among patients who had longer hospital stays.

Factors that contribute to the development of hospital-acquired anemia – such as patient age and sex, chronic kidney disease, and acute inflammation – are not modifiable. But clearly, providers can minimize phlebotomy, Dr. Salisbury and his associates said.

This study was retrospective and observational and so could not establish causality. Prospective randomized trials are needed to establish that the blood draws caused the anemia, and to determine whether limiting the number of blood draws and the volume of blood removed for diagnostic testing can prevent hospital-acquired anemia, they noted.

Blood Loss After Phlebotomy Linked to Anemia