If you are like me, about once per quarter you get a call or email from an internal medicine resident, critical care fellow, or someone else charged with leading a quality improvement project about a brilliant idea they had for improving the quality of care in the adult ICU. “Let's draw all microtainer blood specimens”, they proclaim, and are more than willing to share data showing that this will drastically decrease transfusions in the adult ICU. As our core laboratory is now fully automated, in the past I ended up telling them that it sounded like a good idea but was problematic from an operational standpoint. However after several years of such calls and emails, I finally decided to investigate a bit deeper. Before I go on I should add the disclaimer that I am referring to the practice of microtainer use in the adult ICU; there is compelling evidence that reducing phlebotomy loss in the NICU can reduce blood transfusions.
I first investigated the current practice in our ICUs. For two ICU areas, all orders for blood draws and amount of blood drawn were recorded for a single day. The mean number of blood draws per day was 7.6 (range 1-20), so patients in the ICU were accessed for blood on multiple occasions each day. Mean volume of blood drawn per day was ~ 30-40 cc (range 1-135), and almost all patients with > 100 cc drawn during the day had blood cultures ordered. The most common tests ordered were bedside glucose (82% of orders, requires < 100 µL blood), ABG (24% of orders, requires 1-3 cc blood), electrolyte tests (21% of tests, requires 5 cc), PT (15% of orders, requires 2.7 cc), and CBC (5% of tests, requires 3 cc blood). My enthusiasm for moving towards all microtainers decreased after gathering this data, as most test requests would not be affected by the move (most test requests are for bedside glucose or ABG).
But what evidence exists on whether reducing phlebotomy loss in the adult ICU impacts transfusion requirements? Clinicians who call about this issue often cite older studies and reviews that suggest that phlebotomy loss in the ICU (especially during the first week) averages 200-300 cc per day, and that phlebotomy loss alone may account for 50% of variability in transfusion practice in the ICU (1). However these studies were done at a time when central laboratory equipment used much more blood, and before labs had taken an active approach to reducing blood volume requirements for common tests. Newer data suggests that average blood loss in the adult ICU is ~ 20-40 cc per day (2,3), consistent with what we observed in our ICUs. One recent large study examining development in anemia after myocardial infarction found that the risk of anemia increased by 18% for each 50 cc blood drawn during the ICU stay (2). While still a significant association, this is much weaker than the association between phlebotomy loss and development of anemia published in earlier studies. A second recent smaller study of 100 patients in a single ICU found that while phlebotomy loss was related to the total number of transfusions received, it was not related to the odds of developing anemia (3).
Recently I have therefore taken a somewhat more pessimistic view of the idea that converting all adult ICU blood draws to microtainers will significantly impact the number of transfusions in the ICU. Even if this relationship does exist, I believe that other means (reviewing standing orders, protocols, etc) would be more effective than universal microtainer draws in addressing anemia in the ICU. What is your practice regarding microtainer use in the ICU, and what is your opinion regarding the value of universal microtainer use in the adult ICU?