Introduction to the clinical laboratory

Organization of the clinical laboratory

Laboratory medicine is the medical discipline that applies clinical laboratory science to the care and diagnosis of patients. Laboratory tests are used for four main purposes:

• To document the good health of a patient
• To screen patients for diseases and conditions such as diabetes, high cholesterol, or urinary tract infections (UTIs)
• To help the provider diagnose a medical disease, disorder, or condition
• To help the provider decide on the most appropriate treatment, to monitor the effects of medications and treatments, and to monitor a disease process

Healthcare providers order laboratory testing for patients. Patient specimens are collected at the laboratory, an ambulatory care facility, or home. A specimen is a sample of body fluid, waste product, or tissue collected for analysis. Once in the laboratory, the specimen is processed and directed to the proper laboratory department. Each department of the lab will analyze and evaluate the specimen based on specific tests ordered by the provider. Tests can be performed manually (by hand) or through a variety of specialized automated instruments. Once test results have been completed, they are reported to the provider.

Role of medical assistants

When the healthcare provider orders a laboratory test for a patient, the medical assistant can enter the provider’s order into the laboratory ordering system. The medical assistant may also do the following:

• Provide the patient with specimen collection instructions.
• Collect and label patient specimens.
• Assist with preparing specimens to be transported to a laboratory for testing.
• Perform CLIA-waived testing.

The medical assistant must be knowledgeable about the patient preparations, testing procedures, and the normal range of results for common tests. The medical assistant must carefully follow all laboratory instructions. Excellent communication between the team members and the patient is very important. The medical assistant should make the patient feel at ease with these procedures and hopefully gain the patient’s cooperation and trust.

Organization of the clinical laboratory

There are certain components found in all clinical laboratories. Personnel are needed to staff the laboratory; certain tests are performed in the laboratory, and there are different departments performing those tests. The following sections discuss each of those aspects of the clinical laboratory.

Personnel in the clinical laboratory

Medical laboratories are in hospitals, ambulatory care facilities, public health departments, health maintenance organizations, and referral laboratories (also called reference laboratories). The clinical laboratory is staffed with a variety of professionals, including the following:

• A director may be a pathologist or a clinical laboratory scientist with a doctorate degree. In ambulatory care facilities, the lab director may be the physician. This type of lab is referred to as a physician’s office laboratory (POL).
• Clinical laboratory scientists (CLSs) and clinical laboratory technicians (CLTs).
• Medical laboratory assistants (MLAs) and phlebotomists. MLAs and phlebotomists have received specialized training in the collection of blood samples and the preparation of laboratory specimens.
• Medical assistants (CMAs, RMAs, CCMAs). Medical assistants are trained to properly collect patient specimens and perform specific testing procedures within the POL. They are also trained to properly collect specimens that are sent to outside reference laboratories for testing.

Clinical laboratory testing

Clinical laboratory testing is used in conjunction with a thorough health history and physical examination to obtain essential data for screening, diagnosis, or management of a patient’s condition. The body is healthy when a state of equilibrium exists in the internal environment. This healthy state of equilibrium, called homeostasis, occurs when the physical and chemical characteristics of body substances are within a certain acceptable range, known as the normal range or reference range. A normal or reference range is a numeric range of test values for which the general population consistently shows similar results 95% of the time. A change in the internal environment of the body often results in abnormal test values, which are outside the population’s reference range.

When a provider uses a laboratory test for diagnosis, the patient’s results are compared with the reference range of values. Reference values are also useful for assessing the progress of a patient’s course of treatment. Each medical institution will establish its own reference ranges. It is important for medical assistants to be familiar with the ranges for their institution.

Abnormal values for a test may be seen with more than one pathologic condition. For example, a decrease in a patient’s hemoglobin level is seen in iron-deficiency anemia, but also in hyperthyroidism and cirrhosis of the liver. Therefore, providers cannot rely solely on one laboratory test to make a diagnosis. They must use a combination of results obtained from the history and physical exam and a number of diagnostic and laboratory tests.

Types of clinical laboratory tests

Tests performed in a clinical laboratory range from simple screening tests of one analyte (e.g., measuring glucose to diagnose or monitor diabetes) to complex profile testing, where more than one analyte is tested from a single sample. The tests are all associated with an organ or disease (e.g., performing a lipid profile to determine the various fats in the blood).

A screening test examines a specimen for the presence of an analyte that may indicate a disease state. Screening tests are not necessarily diagnostic for one disease; rather, they indicate that a disease state may exist. Screening tests are routinely done on patients based on their age, history, or gender.

Types of test results

Clinical laboratory tests can be reported in three different ways:

• Qualitative: Test results are reported as positive or negative. A numeric value is not attached to the result. A CLIA-waived mononucleosis test is reported as either positive or negative.
• Semi-quantitative: Test results do not indicate a precise amount of a substance present but an estimate of how much is present. These test results are less precise than quantitative test results but they are more precise than qualitative test results. Semi-quantitative test results may be indicated as “trace amount” or “1+, 2+, or 3+”. Urine dipsticks are examples of semi-qualitative tests.
• Quantitative: The test result is expressed as a number, usually with units of measure attached to numeric values. It is essential that quantitative test results be reported with the units of measure. A CLIA-waived blood glucose test is reported with a number followed by mg/dL (e.g., 120 mg/dL). The abbreviation mg/dL means milligrams per deciliter.

Departments of the clinical laboratory

Large laboratories are divided into various departments, which may include urinalysis, hematology, chemistry, microbiology, specimen collection and processing, blood bank (immunohematology), coagulation, immunology/serology, histology , cytology , toxicology , and special chemistry. A POL generally performs test procedures in urinalysis, hematology, chemistry, and microbiology.

Some larger laboratories use the core laboratory concept, which combines clinical hematology, immunochemistry, chemistry, toxicology, and coagulation into one automated process. The core concept provides for faster turnaround times.

Urinalysis

Urinalysis includes the physical, chemical, and microscopic examination of urine. As part of the physical examination, the color, clarity, and specific gravity are noted. The specimen’s temperature may also be measured to verify that the sample is at body temperature and, therefore, recently collected. Urine is tested with a multiple test strip, also called a dipstick, which tests the following analytes in urine: glucose, protein, ketones, blood, bilirubin, urobilinogen, nitrites, and pH. Microscopically, the provider may examine urine for the presence of red blood cells (RBCs), white blood cells (WBCs), epithelial cells, mucus, casts, crystals, and microorganisms. Additional quantitative tests may be performed in the urinalysis department of a reference laboratory to confirm routine screening test results.

Hematology

Hematology is the study of blood cells and coagulation. Laboratory testing in the hematology department may be qualitative or quantitative. In a POL, screening tests for hemoglobin, hematocrit, and the International Normalized Ratio ( INR , a coagulation test) are typically performed in the ambulatory setting. Reference laboratories will perform blood cell counts that determine the number of RBCs, WBCs, and platelets in a blood sample. Microscopic tests determine the characteristics of cells, such as size, shape, and maturity. In addition, the hematology department performs tests to determine the coagulating ability of blood.

Chemistry

The clinical chemistry department analyzes the chemicals found in blood, cerebrospinal fluid, urine, and joint fluid (synovial fluid). Specimen testing may be done manually or with complex chemistry instruments. In a POL, procedures may include single analyte tests (of blood glucose) or multitest profiles. Chemistry profiles include tests for a number of related analytes. Lipid profiles, for example, include assessments of total cholesterol, triglycerides, low-density lipoprotein (LDL), and high-density lipoprotein (HDL). POL chemistry analyzers are becoming more common in ambulatory care as technology becomes more compact and easier to use.

Microbiology

Microbiology involves the study of very small, infectious organisms such as bacteria, fungi, yeasts, parasites, and viruses. Specimens used in microbiology include blood, urine, sputum, cerebrospinal fluid (CSF), stool, wound material, and other biological sources. Specimens used for microbiology testing must be collected aseptically in sterile containers.

The goal of the microbiology department is to identify the microorganism causing the infection. The staff will also determine the most effective antimicrobial medications, which include antibiotics. This process is called identification and sensitivity (or susceptibility) testing.

Microbiology specimens may be grown on culture media . Once the organism is growing, and in pure culture , it can be identified. Organism identification tests have changed with technology and will continue to change in the future. A variety of methods and technologies are applied to identify the microorganism. Methods include biochemical, molecular, and antigen-antibody complex testing.

Sensitivity testing is performed on organisms to establish an appropriate antibiotic therapy for specific bacterium or fungi. Once again, a variety of techniques and technologies may be used to help determine which antibiotic would be most effective. In a POL, this may include the following:

• Rapid strep testing may be performed to screen for strep throat
• Microbiologic specimens may be aseptically collected and then sent to a reference laboratory
• Some microscope slides may be prepared for the provider to examine
• Identification and sensitivity tests are usually performed in larger centralized ambulatory care, hospital, or reference laboratories.

Identification and sensitivity tests are usually performed in larger centralized ambulatory care, hospital, or reference laboratories.