Bench-top centrifuges have remained a critical piece of equipment in today's laboratory ever since their invention back in the mid-1800s.¹ Today's centrifuges not only separate serum and plasma but also play an important role in helping laboratories achieve Lean by reducing waste and improving productivity.

One of the main principles of Lean is to move from batch processing to "just-in-time" processing. Traditionally, laboratories employed batch processing through the use of a large-capacity centrifuge, where a large amount of tubes are spun for 10 minutes in batches. Batch processing is considered a type of waste in Lean as batching creates excessive work in progress and excessive waiting. 

To reduce waste, the use of high speed low capacity centrifuges have become more commonplace as they allow the lab to reduce batch sizes and centrifugation time, thereby reducing work in progress and waiting.  Another advantage is the smaller footprint of high-speed low-volume centrifuges means that they can be placed at the immediate processing and testing area instead of a centralized location, which can reduce unnecessary motion.

By selecting the right centrifuge, the lab can achieve better turnaround times, reduce waste and improve ergonomics. It is important for labs to examine workflow, space and needs when purchasing centrifuges as each vendor and model has its own advantages and disadvantages. Below are factors that the lab should consider when deciding on the type of centrifuge to purchase.

• Types of Tubes -- Unlike the large capacity centrifuge, the smaller high-speed centrifuge has more limitations in terms of the types of tubes that it can accommodate. Some models are limited to spinning only a few tube sizes, while others require the use of different adaptors or inserts to accommodate different size tubes. Due to the high RCP, glass tubes, regardless of size, should not be spun with a high speed centrifuge.
• Rotor -- The two most common types of rotors are horizontal and fixed angle. Gel tubes spun with a horizontal rotor will have a flat gel barrier which is preferable for chemistry and immunoassay testing. One disadvantage of horizontal rotors is that they generally cannot achieve platelet-poor plasma (platelet count of < 10,000) with shortened spin time (< 3 minutes). Gel tubes spun with a fixed angle will result in gel barriers that are slanted proportional to the angle of the centrifuge. The lower the angle, the flatter the gel barrier will be. Most fixed-angle high speed centrifuges have an angle between 20 to 45 degrees. A slant gel can create problems with certain chemistry and immunoassay analyzers, depending on the mechanism of aspiration and the angle of the slant.
• Spin time -- It is important to consider the total time, which includes both acceleration and deceleration time, when comparing spin time. Depending on the model and RPM, the acceleration and deceleration times can vary quite significantly and account for a significant portion of the total spin time.
• Capacity -- Capacity usually ranges from 4 to 12 regular size sample tubes. Some models even have slots for microtainers that allow them to be spun without the use of an adaptor. It is important to keep in mind that there might be limitations in terms of the types of tubes that can be spun at once. For example, a high speed centrifuge with an 8-place rotor might be able to spin eight 13x75 tubes but only four 13x100 tubes at once.
• Physical layout -- Since Stat centrifuges are likely to be placed close to the processing and testing area, their size and weight should be considered to ensure that they will fit the current layout. Also, as Stat centrifuges are placed closer to the bench along with other analyzers and equipment instead of a separate area, sound levels can become a concern. CAP and OSHA require labs to provide protection when sound levels are equal to or exceeding an 8-hour time-weighted average of 85 decibels.²
• Operators -- The lab should consider its centrifuge operators when making a decision. Centrifuges that require the use of different adaptors or inserts or the use of a mix of fixed-angle centrifuges (for coagulation) and swing buckets (for chemistry) can be confusing unless there are dedicated operators. 
• Demo -- Vendors usually can offer demo unit to the lab for free, therefore allowing the lab to test out the centrifuge in live environment prior to purchasing.

As more focus on Lean processing is being placed in the pre-analytical phase of testing, decreasing centrifugation time by deploying Stat centrifuge is perhaps one of the easiest ways to improve TAT. Selecting the right centrifuge requires a detailed understanding of the lab's current processes, and by reviewing the current processes, lab managers may be able to identify where waste that can be eliminated.  

Michael Yu is area laboratory manager, Kaiser Permanente Panorama City Hospital, CA

References

1. Buie, J. (2010, May 07). Evolution of the lab centrifuge. Lab Manager Magazine, 5(4), 38. Retrieved from http://www.labmanager.com/?articles.view/articleNo/3666/article/Evolution-of-the-Lab-Centrifuge
2. College of American Pathologists (2012, Sept 5). Laboratory General Checklist.