Small-Volume Blood Sample Tubes May Reduce Anemia and Transfusions in Intensive Care

Using small-volume rather than standard-volume collection tubes to draw blood for laboratory testing may reduce the incidence of anemia and the need for red blood cell (RBC) transfusion in intensive care units (ICUs), according to a new study. The change does not appear to impair biospecimen sufficiency for lab analysis.

In addition, by reducing blood transfusion during ICU admission by about 10 units per 100 patients, the change may enable hospitals and health systems to sustain blood product supply during ongoing worldwide shortages.

"It doesn't take long working in a hospital or being a patient or family member to realize how much blood we take to do lab work. As a result, patients may develop anemia and low RBC counts, which can be associated with worse health outcomes," lead author Deborah Siegal, MD, a hematologist at the Ottawa Hospital and associate professor of medicine at the University of Ottawa, told Medscape Medical News.

"Unfortunately, the majority of the blood we take is discarded as waste," she said. "Here's an opportunity to move the needle on reducing anemia in hospitalized patients, where the benefit also doesn't come at a cost."

The study was published online October 12 in JAMA.

Reducing Blood Loss

Among ICU patients with critical illness, there is a high prevalence of anemia, Siegal noted. More than 90% of these patients have some degree of anemia after a 3-day stay. Typically, RBC transfusions are given to correct the low blood counts, and as much as 40% of ICU patients receive at least one RBC transfusion. Anemia and RBC transfusion are each associated with adverse outcomes, including higher mortality and longer ICU and hospital stays.

Although anemia in critically ill ICU patients can have several causes, blood sampling can be substantial because of the need to draw multiple tubes several times per day. During 8 days in an ICU, the amount of blood drawn equals about 1 unit of whole blood, the authors noted, and ICU patients often struggle to increase RBC production and compensate for blood loss.

Even then, only 10% of the blood collected is required for lab testing; the remaining 90% is often discarded as waste, the authors noted. Small-volume tubes (1.8 to 3.5 mL), which are designed to draw about 50% less than standard-volume tubes (4 to 6 mL) by using less vacuum strength, are of the same size and cost as standard-volume tubes, and the collection technique is the same. They are produced by the same manufacturers and are compatible with existing lab equipment.

Siegal and colleagues conducted a stepped-wedge cluster randomized trial to test the switch to small-volume tubes in 25 adult medical-surgical ICUs in Canada between February 2019 and January 2021. They analyzed data from more than 27,000 patients admitted to the ICU for 48 hours or longer. ICUs were randomly assigned to switch from standard-volume tubes to small-volume tubes for lab testing. The research team primarily assessed RBC transfusion in units per patient per ICU stay, as well as hemoglobin decrease during ICU stay, length of stay in the ICU and hospital, mortality in the ICU and hospital, and specimen tubes with insufficient volume for testing.

In a primary analysis of 21,201 patients, which excluded 6210 patients admitted during the early COVID-19 pandemic, there was no significant difference between tube-volume groups in RBC units per patient per ICU stay (relative risk [RR], 0.91). However, there was an absolute reduction of 7.24 RBC units per 100 patients per ICU stay in the small-volume group.

In addition, in a prespecified secondary analysis of 27,411 patients, RBC units per patient per ICU stay significantly decreased (RR, 0.88) after the switch to small-volume tubes, and there was an absolute reduction of 9.84 RBC units per 100 patients per ICU stay.

Overall, the median decrease in transfusion-adjusted hemoglobin wasn't significantly different in the primary analysis but was lower in the secondary analysis. The frequency of specimens with insufficient volume for testing was low (≤0.03%) before and after the transition to small-volume tubes.

About 36,000 units of blood were given to ICU patients during the study period. The use of small-volume tubes may have saved about 1500 RBC units, the authors estimated.

"This could be an important way to help preserve the supply of blood products for patients who need them, including those undergoing cancer treatment, surgery, trauma, or other medical illnesses," Siegal said. "The other great aspect is that this was implemented by people on the ground in the ICUs, and it's still in use in most of those hospitals today."

The investigators noted the need to study the switch in other patient populations, such as non-ICU hospitalized patients or outpatient settings. For instance, ICU patients often have central venous or arterial catheters for blood draws, but small-volume tubes can be used with venipuncture and could lead to additional benefits there as well.

Implementing Change

Commenting on the findings for Medscape, Lisa Hicks, MD, a hematologist at St. Michael's Hospital and associate professor of medicine at the University of Toronto, said, "Routinely collecting smaller volumes of blood for diagnostic testing appears to be feasible and does not cause problems with inadequate sampling. Whether this strategy decreases transfusion is more complicated." Hicks did not participate in the study.

"At the end of the day, we still don't know with certainty whether reduced-volume blood collection tubes decrease transfusion burden in ICU patients — it's possible that there are so many other factors driving down hemoglobin in this population that the impact of blood collection volume is modest to negligible," she said. "On the other hand, it's also possible that there is an important impact that was masked by the relatively short ICU stays in the included population."

Hicks has researched ways to reduce unnecessary diagnostic phlebotomy in ICUs. She and colleagues found that targeting clinicians' test ordering behavior can decrease blood draws and RBC transfusions.

"What we now know, thanks to Siegal et al, is that we don't need to collect nearly as much blood from our ICU patients as we do, raising the question of which strategy should really be standard," she said. "My vote goes for more blood in the patient and less in the bin."

The study was funded by a peer-reviewed grant from the Academic Health Sciences Centers AFP Innovation Fund/Hamilton Academic Health Sciences Organization and the Hamilton Health Sciences Research Institute through the Population Health Research Institute. Siegal, who is supported by a Tier 2 Canada Research Chair in Anticoagulant Management of Cardiovascular Disease, reported honoraria for presentations paid indirectly to her institution from BMS-Pfizer, AstraZeneca, Servier, and Roche outside of the submitted work. Hicks reported no relevant financial relationships.

Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape, MDedge, and WebMD.

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Image 1: University of Ottawa

Image 2: Unity Health Toronto

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Cite this: Small-Volume Blood Sample Tubes May Reduce Anemia and Transfusions in Intensive Care - Medscape - Nov 30, 2023.