Quality Control for the In-Clinic Laboratory

Chapter 66


Quality Control for the In-Clinic Laboratory





Background



Why Quality Control: Rationale for Implementation


The concept of the in-clinic laboratory that consists of reagent kits and instrumentation originated in the mid-1970s. Today the concept has evolved to the use of complex instrumentation with capabilities in hematology and chemistry matching those of the central laboratory. More than 80% of veterinary facilities now have such in-clinic laboratory instrumentation. This trend has occurred with no regulatory oversight of either laboratory quality assurance or instrumentation performance claims. Any leadership in quality control recommendations or procedures has been left to the discretion of instrument suppliers.


Complex instruments perform a complicated series of functions to produce laboratory data. Mechanical components include pipetting mechanisms, addition of diluents and reagents, reaction-sample mixing, reagent stability, and sample movement to or through a measuring mechanism. Measuring components may include various transducer mechanisms or light sources that interact with the reacted sample. The physical elements may include tubing, valves, printed circuit boards, stepper motors, syringes, light-emitting sources, photodetectors, and data-reduction software. Most of these elements are variably subject to wear and eventual failure. Superimposed on this is user interaction with the sample and the system. In the in-clinic environment there is variable laboratory supervision and variable training in laboratory science among users.


The result is a complex operation that requires regular monitoring of performance accuracy. Because the in-clinic veterinary laboratory provides actionable patient data, it is regarded as equivalent to a professional diagnostic laboratory, perhaps with a limited list of services. Professional laboratories implement a standardized plan to monitor each instrument system with quality-control material at least once each shift. In high-volume settings, even more frequent monitoring may be interspersed with processing of patient samples. The authors believe this monitoring can be somewhat simplified for the veterinary practice facility. An analysis of a quality-control material once per day of use is the recommended minimum. The accumulation of daily data allows identification of a developing trend or pinpoints when system failure occurs. Analysis of quality-control material once per month or only when a problem is suspected does not allow identification of a trend or pinpointing of the time of failure.


Rather than trying to sell the merits of a quality-control program, it may be more convincing to present an example. A hematology quality-control material has a total white blood cell (WBC) target range of 12 to 14 × 103/µl. On a given morning, someone is suspicious about the fact that WBC count has been low in an unusual fraction of tested patients and decides to analyze the control material. The system produces a value of 6.4 × 103/µl. The question then is, How do you feel about interpreting WBC values for your patients for the rest of the day? Further, do you have a concern about your interpretations over some number of preceding days? Implementation of a standardized program that analyzes quality-control material on a regular basis before patient testing minimizes such uncertainty. This provides confidence in the results obtained up to that point. It does not, however, guarantee results produced in the future.



Role of Animal Health Diagnostics Companies


Unfortunately, the companies marketing instruments have been variably informative about quality control. At one extreme is the lack of availability of quality-control sample material for some instrument systems. At the opposite extreme is a recommended program of daily control sample analysis with supporting data management software that is patterned after minimal standards for a professional laboratory, but with which compliance is optional and is not monitored. In the middle are numerous recommendations, an example being to analyze a quality-control sample once per month. Some systems claim to have various mechanisms of internal quality control. Although there are procedures for monitoring electronics, these are not a substitute for analysis of a quality-control material that consists of blood or serum, which also allows monitoring of operator technique and the reagent system. The absence of quality control in the diagnostic product offering plays to concerns about cost and the expertise required to implement a quality-control program. Ironically, some people believe that a system with a quality-control program is inferior to one without. Statements like “If it requires daily quality control, it must be unreliable or malfunction frequently” actually are heard. Companies with the product offerings may unknowingly reinforce the perception that quality control is not important. This creates the impression that sales are more important than the reliability of data for medical case management.


The veterinary community, acting as individuals and through organized veterinary medicine, should encourage diagnostics companies to provide and integrate quality-assurance programs. The opportunity now exists for companies to become responsible for monitoring, analysis, and preemptive technical support in the following way. Modern instrument systems have computing power and connectivity to enable bidirectional communication via a network and the Internet. With that capability, it is possible to automate analysis and monitoring of quality control by the supplier. The supplier’s technical support personnel could then proactively intervene when quality-control analysis suggests a potential problem. With the supplier assuming much of the responsibility for the inherent complexity, this approach could standardize quality assurance across veterinary facilities. This approach has the potential to assert expertise that often is lacking or not consistent in veterinary facilities.



Implementations for Chemistry and Hematology Analyzers


The authors believe the quality-control program can be somewhat simplified for the veterinary practice facility. The most practical way to integrate quality control is to include it as part of daily start-up procedures, typically in the morning when the workday is begun. Most systems are in a stand-by mode when personnel arrive in the morning. Most benchtop units have a wake-up or start-up procedure. Analysis of a quality-control material at the conclusion of the start-up procedure verifies that the system is working properly and is ready to analyze patient samples. The procedure involves handling the quality-control material according to manufacturer directions. The material is accompanied by target values determined by repetitive reference procedures. These are expressed as a range for each measurement. Results from the analyzer are expected to fall within this range on a daily basis when all elements are functioning properly. The software of most benchtop instrument systems can store control range values and present control analysis results for inspection. The system also should be able to store control data in a way that can be retrieved for trend analysis. Additional background on quality-control procedures is available (Weiser and Thrall, 2007). More advanced treatment of quality-control data is discussed later in the chapter.



Adjunct Procedures That Supplement Routine Use of Quality-Control Material


Laboratory professionals use a variety of procedures to corroborate anomalies in laboratory data. These also may be used to evaluate data that do not fit a preconceived clinical impression when consulting with the clinician. Some of these techniques may be used in the practice setting. These include the following:



• Sample evaluation. Occasionally, results may be obtained that do not fit the clinical picture or preconceived expectations. When this happens, the sample and sample handling should be evaluated. In blood chemistry analyzers, the presence of interfering substances such as those associated with lipemia or hemolysis, the presence of fibrin clots interfering with sample loading, and improper anticoagulant use are considerations for evaluation. In hematologic testing, the adequacy of sample mixing and the presence of microclots in the sample are considerations, as are hemolysis or lipemia. Instrumentation suppliers should provide guidelines for this evaluation, and their technical support personnel may provide additional help in the evaluation when needed. One should keep in mind that it may be appropriate to repeat the analysis when an unexplained aberrant value occurs.


• Use of quality-control material outside the routine cycle. In addition to performing regular analysis of quality-control material at the beginning of each day, occasionally it is appropriate to check system function with quality-control material whenever it is suspected that analytical failure may be occurring.


• Blood film examination. It is important to note that the capability of hematology analyzers to produce a differential distribution is not intended to replace blood film review of leukocytes. At best, it is intended to detect a reasonably normal hemogram. Furthermore, there is no good quality-control material for the differential analysis. Hematology analyzers cannot detect abnormalities such as left-shifted cells, leukemic cells, nucleated erythrocytes, and other abnormal cell types. When there is leukopenia, leukocytosis, an abnormality in the differential distribution, or any abnormality in the instrument’s histogram or cytogram display, a blood film scan should be performed to corroborate the generated differential data as well as to evaluate erythrocyte morphology and screen for hemoparasites. A differential count should be performed by microscopy whenever a discrepancy or abnormal cells are detected by the scan.


• Evaluation of mean corpuscular hemoglobin concentration (MCHC). The relationship between hemoglobin concentration (Hb) and hematocrit (Hct) is a physiologic constant. These two values are used to calculate the MCHC: MCHC = (Hb × 100)/Hct. The MCHC is typically 32 to 36 g/dl, with minor variation among instrument systems. Because the two primary measurements are performed independently by taking separate measurements on two separate dilutions, they can be used to corroborate each other. Certain pathologic conditions, including iron deficiency and marked regeneration, may cause a minimal decrease in MCHC (e.g., to 30 g/dl). Certain sample abnormalities may variably increase MCHC by artifact, including marked lipemia, sample hemolysis, pathologic red blood cell (RBC) agglutination, and marked numbers of Heinz bodies. Occasionally an Hct value does not meet clinical expectations. There are two readily available means to evaluate this. One is to corroborate the Hct value with the Hb concentration. This is most easily done by examination of the MCHC value; if it is in the physiologic reference interval, the Hct and Hb are confirming each other. A nonsensically low MCHC value indicates an analytical malfunction. A very high MCHC value may indicate the same after sample abnormalities such as marked lipemia, marked sample hemolysis, prominent RBC agglutination, and marked numbers of Heinz bodes are ruled out. The second method is to compare the instrument-derived Hct with a manually obtained packed cell volume. Results for the two methods should match within a reasonable limit, provided the collection tube is filled properly. This limit may vary slightly with the instrument and the patient’s disorder. Failure of the results to match can localize the source of the nonsense MCHC values to the RBC counting and sizing. In addition, the centrifuged microhematocrit tube provides a simple means of examining the supernatant for hemolysis and lipemia. If nonsense values are obtained repeatedly, analyzing the quality-control material or contacting technical support is warranted.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Quality Control for the In-Clinic Laboratory

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