Proper design, regulated speeds critical in PTS system designs
by Dennis Ernst • August 02, 2021
Over the years, I've seen numerous studies assessing the impact of pneumatic transport systems (PTS) on blood test results. A new study sheds still more light making this an excellent opportunity to summarize the literature.
The most recent study was a meta-analysis of 29 studies covering 3121 blood samples, and includes some, but not all, of the studies I've reported on in past issues of Phlebotomy Today. That's because the authors focused on hemolysis from pneumatic tube transport more so than it's affects on individual analytes. By extension, they did include studies that assessed levels of potassium (K), lactate dehydrogenase (LD) Alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which are often elevated in hemolyzed samples. LDH, for example, is 160 times more concentrated in red blood cells than in circulating plasma.
The authors concluded hemolysis is not elevated on PTS-transported samples, but LDH levels are increased under certain circumstances. Those circumstances include when the cannister containing the samples travels faster than 19.6 feet/second (6 meters/second) or when the distance traveled was 273 feet or more (250 meters).
Looking further back to other studies, researchers in China assessed the effect of one hospital’s PTS on serum LDH and potassium levels and concluded minor shaking during sample transport influenced LDH and potassium concentrations.(2) The study states that clinical laboratory staff should recognize the negative side of PTS with regards to analyte stability, while the authors also acknowledge previously published studies that found no significant difference in hemolysis frequency between PTS and hand delivery of blood samples. The explanation: differences exist among different transport systems.
Another 2009 study evaluated the excessive rates of hemolysis associated with a recently installed pneumatic tube system in the Accident and Emergency Department of a Scottish hospital. Prior to PTS installation, the weekly mean hemolysis rate reported by the laboratory was 3.3%. A problem with the system resulted in subsequent hemolysis rates as high as 54%. After the fault was corrected and other measures taken, including bubble-wrapping samples, hemolysis rates were 7.1%. The study concludes that laboratories should be aware that defects in a PTS can cause rapid deceleration resulting in increased sample hemolysis rates.(3) Depending on the configuration and speed of a given system, samples transported by a PTS may be subjected to significant agitation en route due to sudden acceleration and deceleration. The study illustrates the need to conduct not only initial but periodic validations of PTSs to ensure proper performance.
In a study conducted in Homburg, Germany, researchers concluded that PTS transport impairs platelet aggregation, with the recommendation to manually transport whole blood samples that are collected for platelet aggregation studies or PFA-100 analysis. In contrast, a Swedish study that evaluated the effect of PTS transport on routine hematology and coagulation studies, including platelet function with PFA-100, found that sample transport by a PTS did not introduce preanalytical error for these tests.
In terms of arterial blood gas (ABG) samples, a study evaluating ABGs transported by a PTS found the partial pressure of arterial oxygen (PaO2) values to be falsely elevated and clinically unacceptable when compared to the results obtained from ABG samples transported by courier.
According to the authors of a 2011 editorial appearing in Clinical Chemistry and Laboratory Medicine, the documented effects of PTSs on sample quality and all laboratory parameters seem limited, if not controversial. Sample transport is an important preanalytical factor that can greatly impact overall turnaround times and sample integrity. When automated processes are implemented, they warrant comprehensive and periodic evaluation to ensure accurate results not sacrificed for the sake of expediency.
Here's the bottom line. PTS transport is a safe, effective and efficient means to transport diagnostic blood samples when designed and installed with consideration for minimizing speeds, distances and sudden stops and starts. If you have physicians questioning your potassium, LDH, AST and ALT results and use a PTS for sample logistics, consider evaluating its effects by conducting your own internal study. Compare test results from samples drawn from the same patient, but transported differently (manually transported versus PTS-transported). Sometimes all that's necessary is a little extra padding and some speed controls.
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