Laboratory Equipment, Part 2
In part 1 of this series, we looked at the basics of laboratory equipment, pH meters, and automated analyzers. In this section we will cover more devices commonly found in clinical lab settings.
The cell washer/cell saver that is used in the operating room as part of an auto transfusion system is different from the cell washer used in a laboratory. In the laboratory the cell washer is sometimes confused with a centrifuge, [see ICC Prep, May]. A cell washer looks and acts similarly to a centrifuge and has most of the same problems, with several major differences:
There should be samples from only one patient at a time.
The whole blood has been previously spun down and the cells decanted to a new tube.
The cells are mixed with 2%5% saline and spun again.
Three to four times additional normal saline (0.9%) is decanted into the tube containing the cells.
The tubes overflow and the waste is collected in an external chamber.
The saline rinses remove serum proteins from the surface of the cells so they do not affect the tests that are performed when reagents are introduced.
Same as centrifuges
Problems with decanting pump for the saline
Overflowing waste container
Coagulation analyzers range from the very simple clot timer, to semi- and fully automatic devices that test all 12 coagulation factors. The automatic devices generally cover both the hemostasisarresting of bleeding (clotting)and homeostasismaintenance of blood fluidity. The machine may use whole blood, plasma, or platelets for testing. Some units can test all three while others may be limited, so as a biomed you have to determine what the medium is before doing any testing on the device.
This small, often battery-operated device is commonly found in cardiac catheterization labs and operating rooms. A tube with a whole blood sample is placed into the well of the unit, which triggers both a small heater and a timer, (some older units may have a start button that has to be pushed). On one side of the tube there is a light and on the other a photo detector. As the blood clots, less light passes through the sample, and, when fully formed, no light passes and the timer stops. This usually takes less than 60 seconds.
Dirty light or photo detector
Automatic Coagulation Analyzers
These are generally large units located in a central laboratory area, sometimes on reagent rental contracts. These units can use all three types of specimens and batch testing is most common. The integrity of the sample must be assured to have accurate results, if the samples are left unrefrigerated for any length of time they may start to clot before any testing is done. Also, if the sample is drawn using too small a needle, cells can be damaged and the sample compromised. (Blood should never be drawn for testing with any needle less than 22 gauge in diameter the higher the number the smaller the diameter.)
Samples are placed into a rack and introduced into the analyzer. This is a mechanical process and alignment is critical for smooth movement. Once in place, various reagents are added to the samples. The tests are done both by electrical conduction and photometric detectors.
While sample collection is not part of what biomeds are responsible for, improperly obtained samples will affect the results. If the majority of the samples are not getting good results, look at the collection process. Samples to be tested in these machines must be collected in plastic, siliconized, or nonwettable glass. Ordinary glass allows the sample to coat the surface and will affect test results. Also investigate the size of the needle used to obtain the samples.
Results are displayed in printed form and some units may be directly linked to a computer that distributes result reports.
Mechanical alignment of the sample trays
Tray transport system in the machine
Reagent delivery problems
Wrong paper used in report generator
Waste product receptacle full.
Like coagulation analyzers, hematology analyzers range from very simple to fully automated systems. Costs range from several hundred dollars to more than $100,000, with wide variations in how many functions the units can perform.
Very simply put, this is a hematology analyzer wherein whole blood sample is injected into the unit and diluted and divided before being aspirated past optical sensors that count cells. In the first sample division, the red cells are counted, the second division counts white cells, and in the third division, platelets are counted. The results are displayed on a screen or printed on paper. These units are used for quick counts for patients in clinics and physician offices. The ability to accurately count platelets is questionable in many of the simple units. Also these simple units do not adequately count immature cells, particles or do any serum testing.
Though no longer in wide use, you might encounter a platelet counter in a clinic. This works the same as a cell counter but was designed to count just platelets.
Low suction levels so samples do not aspirate
Wrong paper in the printer
Tubing leaks, especially in the suction line
Incomplete flush between samples
Most hospitals have automated hematology analyzers that combine the tests performed by cell counters with some of the tests done by coagulation analyzers and may include testing for certain proteins, serum, or particles.
Since these systems perform tests on samples from many patients, sample identification is critical (this is also true of a hematology analyzer that has a loading carousel). The samples are prepared and placed in racks that are transported automatically into the system. The samples are diluted and aspirated into the system and separated from one another by air, flush solution, or water. As samples pass from detector to detector, reagents can be added automatically for specific tests. Test results are printed out with patient identification. On some units, if a fault occurs on a testing step, all other tests are stopped and cannot be restarted until the fault is corrected. On other systems, the unit will keep running and just not perform the test where the fault has occurred. Once the rack has been completed, the unit will not accept another test rack until the fault has been corrected. You need to know how the system handles faults as it can affect when service can be performed. On the automated systems, suction is generally obtained from the hospitals central system. Central suction problems will affect a units ability to aspirate the samples into the detectors. This is often the cause of contaminated readings, as the flush solutions are incorrectly drawn through the system.
Water treatment systems should be considered part of the system when troubleshooting. If water pressure drops due to clogged filters, the system may stop until the pressure is returned to the correct levels. Mineral build up in the water system is becoming a problem in many parts of the country. Flow rates and pressures will often change as the hospital pipes get mineral buildup, requiring more frequent filter changes.
With all automated analyzers problems with the physical facility can and do cause the devices to malfunction so you should be aware and check externally, for construction or renovations, before getting into troubleshooting the units.
Bad or incomplete detector chamber flush
Loss of suction
Drop in water pressure
Voltage drops or spikes
Reagent or mixing pump failure
Misaligned racks on the transport track
|1) How many coagulation factors are tested on an automatic system?
2) How many times are blood cells rinsed with normal saline in a cell washer?
3) Clot timers are most commonly found in
All answers are A.
David Harrington, PhD, is director of staff development at Technology in Medicine in Holliston, Mass.
Contributing to this article is Eric Massey, a TiM biomed at Women and Infants Hospital in Providence, RI.