Basic Concepts of Quality Assurance in the Hematology Laboratory

BASIC CONCEPTS OF QUALITY ASSURANCE PLANS IN THE HEMATOLOGY LABORATORY

Quality assurance is a comprehensive and systematic process that strives to ensure reliable patient results. This process includes every level of laboratory operation. Phlebotomy services, competency testing, error analysis, standard protocols, PPE, quality control, and turnaround time are each a key factor in the quality assurance system. From the time a sample arrives in the laboratory until the results are reported, a rigorous quality assurance system is the key feature in ensuring quality results. Each part of the quality assurance plan or process should be analyzed, monitored, and reconfigured as necessary to emphasize excellence at every outcome. Although many hospitals and research facilities have “quality” professionals who provide oversight for quality assurance plans for their facilities, an elemental understanding of terms related to the total quality assurance plan is required of all staff technologists and students. 

Quality control is a large part of the quality assurance program at most facilities. Students will be introduced to the term quality control early and often. It is an essential function in the clinical laboratory. The information that follows provides a brief overview of the quality control procedures used in promoting quality assurance in the hematology laboratory. It is not intended to be comprehensive but introduces terminology and concepts pertinent to the entry-level professional.

Quality Control Monitoring in the Hematology Laboratory

The analytical component, or the actual measurement of the analyte in body fluids, is monitored in the laboratory by quality control, a component of the laboratory quality assurance plan. Similar to the chemistry laboratory, the analytic method in the hematology laboratory primarily includes nstrumentation and reagents. Standards, or calibrators, are solutions that have a known amount of an analyte and are used to calibrate the method. A standard, or calibrator, has one assigned, or fixed, value. For example, the hemoglobin standard is 12 g/100 mL, meaning that there is exactly 12 g of hemoglobin in 100 mL of solution. Conversely, controls, or control materials, are used to monitor the performance of a method after calibration. Control materials are assayed concurrently with patient samples, and the analyte value for the controls is calculated from the calibration data in the same manner as the unknown or patient’s results are calculated. Control materials are commercially available as stable or liquid materials that are analyzed concurrently with the unknown samples. The control material measured values are compared with their expected values or target range. Acceptance or rejection of the unknown (patient) sample results is dependent on this evaluation process.

A statistical quality control system is used to establish the target range. The procedure involves obtaining at least 20 control values for the analyte to be measured. Ideally, the repeated control results should be the same; however, there will always be variability in the assay. The concept of clustering of the data points about one value is known as central tendency. The mean, mode, and median are statistical parameters used to measure the central tendency. The mean is the arithmetic average of a group of data points; the mode is the value occurring most frequently; and the median is the middle value of a dataset. If the mean, mode, and the median are nearly the same for the control values, the data have a normal distribution. The standard deviation and coefficient of variation are a measure of the spread of the data within the distribution about the mean. Standard deviation is a precision measurement that describes the average “distance” of each data point from the mean in a normal distribution. This measurement is mathematically calculated for a group of numbers. If the measured control values follow a normal distribution curve, 68.6% of the measured values fall within the mean and one standard deviation (SD) from the mean, 95.5% falls within the mean and two standard deviations (2SD) from the mean, and 99.7% fall within the mean and three standard deviations (3SD) from the mean. The 95.5% confidence interval is the accepted limit for the clinical laboratory.

Coefficient of variation (CV) is the standard deviation expressed as a percentage. The lower the CV, the more precise are the data. The usual CV for laboratory results is less than 5%, which indicated that the distribution is tighter around the mean value. Clarifying accuracy and precision is usually a troublesome task as these terms are often used interchangeably. When a test result is accurate, it means that it has come closest to the correct value if the reference or correct value is known. In most cases, once a methodology has been established for a particular analysis, standard or reference material is run to establish a reference interval. Accuracy is defined as the best estimate of the result to the true value.

Precision relates to reproducibility and repeatability of test samples using the same methodology. Theoretically, patient results should be repeatable if analyzed a number of times using the same method. If there is great variability of results around a target value, then the precision is compromised.

Source : Hematology in Practice - Betty Ciesla

The Microscope

The microscope is an essential tool to the hematology laboratory professional. It is a piece of equipment that is stylistically simple in design, yet extraordinarily complex in its ability to magnify an image, provide visual details of that image, and make the image visible to the human eye. Most commonly used today are compound microscopes, which use two lens systems to magnify the image. The ocular devices on the microscope provide an initial 10 magnification, and then additional magnification is obtained through the use of three or four different powered objectives. A light source is located within the microscope base. Light is beamed to the image directly, or filters are used that vary the wavelength. In addition, a diaphragm apparatus is usually located in the base of the microscope. Opening or closing the diaphragm can optimize or reduce the volume of light directed toward the image. This is most useful when examining cellular structures in the nucleus that need more light to be properly visualized.

Below is a brief description of the most significant parts of the microscope

Significant Parts of the Microscope

The eyepieces, or oculars, are located laterally to the microscope base and function as an additional magnification component to the objective magnification. Most microscopes are binocular and contain two eyepieces, each of which will magnify the diameter of an object placed on the stage to the power of the eyepiece, usually 10.

The objectives of the compound microscope are 10, 40, or 100. Often, a 50 (oil) magnification will be incorporated. Each objective has three numbers inscribed on the objective: a magnification number, an aperture number (NA), and a tube length number. The NA refers to the resolution power of the objective, the ability of the objective to gather light. The higher the NA number, the higher is the resolution. Tube length refers to the distance from the eyepiece to the objective.

Magnification refers to how large the image will appear, as well as how much of the viewing field will be observed. Objectives on modern microscopes are com posed of many lenses and prisms that produce an extremely high quality of optical performance.

The iris diaphragm, located below the microscope stage, increases or decreases light from the microscope light source. If the diaphragm is opened to its full capacity, the cell or structure is viewed with maximum light. If the diaphragm is minimally opened, the cell or structure is much less illuminated, which may be desirable depending on the source of the sample (i.e., hematological cells versus urine casts).

The stage is a flat surface with an opening created for light to pass through. Two flat metal clips have been mounted in which to secure the glass slide. Below the stage surface are two control knobs that move the slide in a horizontal or vertical fashion. Coarse and fine adjustment knobs are located on either side of the microscope base. These adjustments bring the image into focus through movement of the stage, which is either raised or lowered according to the level of focus needed.

Care of the Microscope

The microscope is an essential piece of equipment to the practice of hematology and must be handled with care and respect. Hematology instructors owe it to themselves to teach the care and maintenance of the microscope in hopes that these “best practices” can be adopted and practiced in the workplace. The microscope should be on a level, vibration-free surface. If it needs to be lifted from a storage cabinet to another location, the microscope must be secured on the bottom by one hand and held by the neck with the other hand. Additionally, users must be instructed on how to move objectives from one position to another without dragging non–oil objectives into oil from a slide left on the stage. The high-dry objectives must never be used with oil, only with coverslipped slides. 

Objectives are easily scratched or damaged by careless handlers; consequently, they must be cleaned with lens paper after each use. Oil objectives should be wiped free of oil when not in use, and eyepieces must be cleaned with lens paper from dust, dirt, or cosmetic debris with each viewing. Good microscopy habits should always be cultivated, practiced, and communicated. Microscopy guidelines should be posted in each area where microscopes are used. The guidelines should include

• General use of the microscope

• Instructions for transporting the microscope

• Instructions for proper cleaning of the microscope

• Storage guidelines that include proper position of microscope cording

Corrective Actions in Light Microscopy

Many of the problems that are encountered when using a microscope can be easily corrected by using common sense. Some of the most common “problems” in light microscopy are as follows:

• Image cannot be seen at any power—Try turning the slide over; perhaps the wrong side of the slide has been placed on the microscope stage.

• Fine details cannot be detected in immature cells—For immature cells, use the 100 lens and open up both diaphragms to the maximum width, for maximum light.

• The 40 objective is blurred—Try wiping off the 100 lens; perhaps the 100 lens was oil filled and was dragged across the slide.

• Dustlike particles appear on the slide but they are not large enough to be platelets—- Perhaps mascara has been left on the eyepiece; use lens cleaner to clean the eyepieces.

Source : Hematology in Practice - Betty Ciesla