Blood Bank Process Controls

Vol. 24 • Issue 6 • Page 40

Blood Banking

Quality is engineered into laboratory medicine through process controls. Discrete analyzers monitor temperature, sample position and dozens of other variables to carry out instructions in sequence and generate output within specific ranges. Manual procedures have a greater potential for error because they lack engineered process controls. This article describes how to apply these concepts to improve quality in blood bank tube testing.

Process Control

Process control includes activities that ensure a process is stable, predictable and produces output with a minimum amount of variation.1 It’s commonly used in manufacturing to control complex variables with automated changes that correct out-of-control situations monitored by a process engineer. Control loops of various kinds measure variables and change the process in real time.

One example is your home furnace thermostat. A temperature sensor turns the heat on if the temperature falls below a set point and off when the set point is reached. There is no error correction (no feedback loop). Your furnace is either on or off. Another example is your automobile’s cruise control, in which you define the set point as the desired speed and a controller continuously adjusts the fuel valve as grade, wind speed and other variables affect vehicle drag. The controller also corrects for variation, such as the rate of change to produce a consistent speed.2

Laboratory automation couldn’t exist without engineered process controls. Operating parameters in a chemistry analyzer, for example, such as temperature, sample location, reagent levels, absorbance readings, etc. are monitored at key steps to control the process. Built-in redundancy, control limits and fail-safes in most cases allow the analyzer to stop at a safe point if human intervention is needed.

Engineered process controls can be complex, measuring dozens of variables in a short time, but the concept works with a manual process, too. A home example is drawing water for a bath: Water temperature is determined by two flow controllers that are adjusted manually according to feedback on how hot the temperature feels until it is at the desired temperature.

In the laboratory, some manual tasks are monitored by statistical process control such as control charts. Other variables include storage temperature of reagents, built-in procedural controls and expected reaction strength. But manual lab testing is subject to a wide variation in human behavior, experience and habit. Can greater process control be applied in a high-risk area, such as blood bank tube testing?

Blood Bank Process Control

Tube testing controls vary from one lab to another – size and color of tubes, arrangement of the workstation, use of a centrifuge and/or cell washer, documentation of reactions, etc. As with all process control, a consistent output is desired. Because the output (e.g., the final reaction) is not known during the process, it is “open loop;” adjustments are made to affect the output, but there is no feedback that changes the input.3 Change to the system is made on faith there will be a valid outcome.

These controls can be defined to anticipate and reduce variation by clearly defining the expected output at each step in the process. For example, when performing a front ABO Group typing, antisera is added to two tubes labeled “Anti-A” and “Anti-B.” The expected outcome is that the first tube contains blue reagent; the second, yellow. To ensure a consistent output, your reagent rack may be arranged from left to right, enabling a technologist to grab the Anti-A reagent first. An adjustment to the process would be to rearrange these vials as necessary. Thus, a process control is checking the label and color of the reagent before dispensing.

Adding Anti-A and Anti-B reagents is second nature to experienced technologists, but writing down detailed descriptions of other expected outcomes can reveal subtle opportunities for variation that leads to error. For example, if patient serum is not added first to a three-cell antibody screen panel and is skipped, the tubes containing red cells may look as expected, resulting in a negative result.

Suggestions for Getting Started

Write down the expected outcome of each procedural step. As a group, discuss how this outcome can be affected by variables that can be observed or measured. Since blood bank tube testing is primarily a visual process, describe observable variables such as reagent color, amount of material in the tube, color of material in the tube, strength of reaction, etc.

If an outcome variation is not observable, consider adding an additional control. For example, Rh antisera is clear, creating a possibility of a false negative reaction if LISS is added by mistake. Adding a step to confirm a negative Rh type with known positive cells is a control.

While tube testing is largely a stepwise, discrete process, continuous variables can be monitored as well. These include reagent storage temperatures, heating block temperatures, centrifuge speed and timer operation.

As with any manual process, human factors present the greatest opportunity for variation. Technologists can be distracted, confused or biased to make simple mistakes (e.g., the technologist can be thinking of a recent ABO type and write down that interpretation incorrectly). This kind of variation is difficult to predict and even more difficult to control. Experienced technologists develop good, consistent work habits such as arranging tubes the same way each time, reading and documenting each reaction individually, etc. Including a deliberate element of direct peer observation using the procedure to your competency assessment will help reinforce good habits.

Finally, you should use your information system to control outcomes. Drop-down boxes, reflex comments and delta checking history are examples. In the case of a crossmatch, the selection of types for the donor unit can be limited to those compatible with the recipient. Entering a positive or incompatible result can force additional documentation.

While most of your laboratory may be automated, manual processes like blood bank tube testing remain a challenge to control and reduce variation. By applying a few concepts of engineering process control, your manual procedures can be written to ensure consistency, reduce workarounds and provide better patient care.

Scott Warner is lab manager at Penobscot Valley Hospital, Lincoln, ME.


1. What is process control? Definition and meaning. Available at: Accessed March 8, 2015.

2. Wikipedia. Process control. 2015. Available at: Accessed March 8, 2015.

3. The definition of open loop. Available at: Accessed March 13, 2015.

About The Author

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