Centrifugation and centrifuge maintenance may not be the most exciting topics in laboratory medicine, but they are central to much of the testing we do and important in the quality of tests we provide, as an inadequate instrument or poor procedure can affect test results. Though their care is often neglected, the very high speeds at which centrifuges operate make them high performance instruments that need to be monitored and maintained.
The College of American Pathologists (CAP) only has limited requirements for centrifuge maintenance. The CAP checklists GEN.41017 and COM.30600 require documentation that centrifuge performance is verified at least annually by manufacturer service representatives or a clinical engineer, or more frequently as defined by the manufacturer. Specifically, the centrifuge speed should be confirmed and the lid lock mechanism function verified, as appropriate. In our lab, hospital clinical engineers take care of these annual function checks and maintain the records.
Clinical and Laboratory Standards Institute (CLSI) guidelines in GP31A go into more detail about centrifuge care and maintenance. This document sets out the general recommendations for maintenance, but specifically cites the need for accuracy in centrifuge timers and speed control. GP31A endorses verifying timers against an accurate time source, such as a stopwatch, at various time points. If the centrifuge timer is inaccurate, a correction factor may be applied. The trick with this is ensuring that everyone uses the correction factor every time they use the centrifuge.
Verifying centrifuge speed is a more complicated task, often performed by the manufacturer’s representative or a clinical engineer. Speed verification is assessed across a range of speeds using a calibrated tachometer or stroboscopic light. If the expected and actual speeds do not match, a correction factor can be applied, or the centrifuge should be adjusted and calibrated to run at the expected speed. CLSI GP31A also recommends semi-annual maintenance including checking the condition of braking brushes, gaskets, seals, mounts, and power supply, and replacing any damaged or worn parts. Finally, at least twice per year, and anytime a centrifuge part is removed or replaced, an appropriate lubricant should be applied to bucket grooves, threads, and rubber seals. Proper lubrication is essential to prevent instrument burnout.
Annual performance verification is well and good, but for optimal sample processing, lab staff should be prepared to do routine maintenance and function checks. Laboratorians should all be familiar with the basic operation of centrifuges and the need to check several factors with each run. First, centrifuges must always be balanced. Every centrifuge I’ve ever seen has a rack of water-filled tubes next to it to balance out uneven numbers of tubes. Second, if a sample spills into or breaks while in the centrifuge, staff should know how to disassemble the rotor for cleaning with neutral cleaning solutions and non-abrasive cloths. Of course, if the centrifuge is making strange noises or vibrating, it should be taken out of commission immediately to prevent severe damage to the instrument or user. Additionally, staff every day should inspect the centrifuge—especially the rotor and shaft—for signs of cracking, uneven wear, or corrosion, and they should replace any affected parts.
Suboptimal centrifugation of samples causes poor separation of plasma or serum from cells. Inadequate centrifugation results from insufficient speed or time spinning, or failure of the centrifuge. Figure 1A shows a gel tube that was centrifuged at a speed lower than the manufacturer’s recommendation. Clearly, there is poor separation of the red cells from the plasma. Figure 1B is of a gel tube spun for less than the recommended time. There is extensive penetration of cells throughout the gel, and though difficult to see in the picture, cells appear to be on top of the gel as well.
Several years ago, we discovered that one of our centrifuges at an off-site physician’s office wasn’t functioning properly when we noticed a rash of poorly-separated samples in gel tubes. Moreover, some of the samples weren’t caught, and so were not aliquoted and re-centrifuged before testing. We only identified the problem after the samples failed delta checks for analytes such as potassium and aspartate aminotransferase, which were released from platelets and red cells that lysed once on the chemistry analyzer. Ideally, the staff centrifuging the samples at the off-site office would have noticed the poor sample separation and discontinued use of the instrument until it could be fixed. This just illustrates that the seemingly lowly centrifuge actually plays a crucial role in laboratory medicine. With that in mind, labs that give centrifuges the care and attention they have earned will find these high performance instruments will provide years of dependable service.
Amy L. Pyle-Eilola, PhD, DABCC, FACB, is assistant core lab director at Nationwide Children’s Hospital in Columbus, Ohio.