Tubing Material Selection Can Affect Carryover … Big Time

Posted on May 23, 2017

Labs in the United States run seven to ten billion blood tests annually influencing more than 60% of clinical decision making. On any given day, that’s millions of blood samples running through millions of meters of tubing within today’s most technologically advanced diagnostic instruments. With that many chemistry panels being analyzed, there’s bound to be inaccuracies. The key here is to reduce inaccuracies to as close to zero as possible before a test panel is even run, by optimizing flow path management and through superior fluidic solutions. Carryover from one sample to the next is always a risk.

So, what is Carryover?

Carryover is defined as the remnant of a sample left over in the flow path that gets picked up in a subsequent sample. Although there are several system components which can affect carryover – the aspirate/dispense probe and unswept fluid volume readily come to mind – for now we will focus on tubing material selection.

When a fluid traversing the fluid path picks up some volume of a preceding fluid, it becomes diluted; it no longer has the same concentration. This can be problematic when multiple critical fluids travel through one fluid path.  Changes in concentration can lead to false readings and misdiagnosis.

Materials with low surface energy such as PTFE, FEP, PEEK, ETFE, and MFA are used for the flow path in an effort to reduce fluid carryover. If a fluid flowing through a piece of tubing has a higher surface energy than the tubing itself, it will usually stay bound to itself, and not bind to the inner-diameter surface of the tubing.  This reduces the likelihood of carryover, as the next fluid moving down the flow path may not encounter any of the previous fluid to pick up.

Newly marketed diagnostic instruments and their assays are becoming more and more sensitive. This greater sensitivity is likely to require more stringent control of carryover from one sample being tested to the next. Thus, the tubing choices made for today’s more sophisticated diagnostic analyzers are even more critical than in the past.

Forewarned is forearmed. So, understanding what’s involved with carryover at the onset of a design goes a long way to offering a design solution to help OEMs to solve this problem in today’s more sensitive, precise and faster diagnostic instruments.

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