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Collecting Smaller Blood Samples for Testing May Benefit Patients but Pose Challenges for Labs

In 1999, Jocelyn M. Hicks, PhD, a laboratory director who was hospitalized for several months, developed anemia in the hospital and required several blood transfusions. After she recovered, she was shocked to discover that the anemia was caused by the amount of blood drawn for her lab tests during her admission. This prompted her to survey 19 community, university, and children's hospitals about blood-drawing practices. Hicks discovered that most respondents collected 10 times the volume of blood necessary for routine laboratory testing. About one-half to two teaspoons (2.5–10 mL) of blood was collected for testing that required just one-third teaspoon (1.5 mL) or less.

Little has changed over the ensuing 17 years, despite the fact that modern chemistry analyzers require less than 50 microliters (about a drop) of plasma for a routine comprehensive metabolic panel. Recent publications have shown a direct relationship between patients' ill health and the volume of blood collected for laboratory testing.

Given these findings, it is not surprising that blood-drawing (phlebotomy) has been implicated as a primary cause of anemia occurring during hospital stays (hospital-acquired anemia, HAA). Anemia is characterized by a low number of red blood cells and low hemoglobin and can cause fatigue and weakness. One study found that the rate of hospital-acquired anemia was approximately 45% in patients older than 18 years admitted to an internal medicine inpatient service. Another study of 30 pediatric intensive care units (PICUs) reported a similar rate of 41%. Hospital-acquired anemia also has been associated with higher rates of in-hospital illness and death.

Due to these concerns, there is a constant push to reduce the amount of blood collected in pediatric patients as well as in adults, and in hospitals as well as in out-patient care settings. However, while collecting the very minimal blood volume required for testing reduces the risk of anemia, laboratory testing on smaller blood volumes poses several challenges for clinical laboratories. Here are just a few examples:

Minimum sample required for automated instruments:

• The minimum amount of blood needed to perform tests on an automated instrument depends on the total amount needed for the individual tests plus the amount necessary for the instrument to accurately pick up or aspirate a sample (often referred to as the "dead volume"). The dead volume can be significant depending on the test and instrument. For example, a test might require less than a drop (30 microliters) of sample, but an instrument's dead volume might be 10 times greater.

• Some instruments test for substances in samples that can interfere with testing, such as the presence of hemoglobin from red blood cells that have broken apart (hemolysis). The tests for interferences are usually performed prior to the actual test on chemistry instruments and can add to the total volume required.

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Vol 7 No 6, September 2016 Page No: 56

Tags : clinical laboratories, pediatric intensive care units, blood transfusions, laboratory testing, blood-drawing practices, comprehensive metabolic panel, Medical Journals, GP Clinics