Laboratory testing is a fundamental component of modern healthcare, providing the objective data needed for diagnosis, treatment, and monitoring of health conditions. The volume of this work is immense, with estimates suggesting that over 14 billion clinical laboratory tests are performed annually in the U.S. alone. These tests inform more than 70% of medical decisions. Understanding which biological samples are most frequently processed helps illustrate the focus and capabilities of a high-volume diagnostic laboratory.
The Primary Specimen Type
The most common specimen type tested in the laboratory is blood, which is collected in three main forms: whole blood, serum, and plasma. Whole blood contains both the liquid component and cellular elements like red and white blood cells. It is primarily used for tests that analyze the cells themselves, such as a Complete Blood Count (CBC), and is often collected with an anticoagulant like EDTA to prevent clotting.
Plasma and serum are derived from the liquid portion of the blood. Plasma is obtained when whole blood is collected in a tube with an anticoagulant, preventing clotting. After centrifugation, the cells settle, leaving the plasma on top, which still contains clotting factors such as fibrinogen.
Serum is the liquid that remains after blood has been allowed to clot naturally in the collection tube. The clotting process consumes fibrinogen and other clotting factors, meaning serum lacks these components. Serum is then separated from the clotted cells via centrifugation, offering a cleaner sample for many chemical and immunological analyses. Collectively, samples derived from blood account for the overwhelming majority of testing volume in a clinical laboratory.
Why Blood Testing Dominates Laboratory Volume
The dominance of blood testing stems from its ability to provide a comprehensive, systemic view of the body’s internal state. Blood circulates through every organ and tissue, carrying metabolites, hormones, and immune cells, making it a valuable source of diagnostic information. This breadth of data allows a single blood draw to be used for multiple high-volume tests across various laboratory disciplines.
Hematology, the study of blood cells, is a major driver of volume, with the Complete Blood Count (CBC) being one of the most frequently ordered tests globally. The CBC quantifies red blood cells, white blood cells, and platelets. This data can indicate anemia, infection, inflammation, and potential bleeding disorders, ensuring its high-volume status in both emergency and preventative care.
Clinical Chemistry tests, often performed on serum or plasma, represent a large portion of the testing volume. These panels assess organ function and metabolic health. For instance, the Comprehensive Metabolic Panel (CMP) evaluates kidney and liver function, electrolyte balance, and blood sugar levels from a single sample. Lipid panels, which measure cholesterol and triglycerides, are also routinely ordered for cardiovascular risk assessment.
Immunology and Serology testing also rely heavily on blood samples, contributing significantly to the volume with tests for infectious diseases and autoimmune conditions. These tests detect antibodies or antigens in the serum. The ability to screen or monitor a vast number of conditions through blood analysis solidifies its position as the most common specimen type.
Other High-Volume Specimens in Clinical Labs
While blood dominates, other specimens contribute substantially to the operational throughput of a clinical laboratory, most notably urine and swabs. Urine is the second most common specimen type processed, offering unique insights into the genitourinary system and metabolic function. Urinalysis is a fundamental test that involves physical, chemical, and microscopic examination of the sample.
Standard urinalysis is frequently performed using automated dipstick readers and microscopy to check for signs of kidney disease, diabetes, or urinary tract infections. Urine is also the preferred specimen for drug screening and for specialized tests like the 24-hour collection, which provides a cumulative measure of substances like protein or creatinine clearance.
The volume of testing on swabs has increased due to the expansion of molecular diagnostics for infectious diseases. Swabs collect material from sites like the nose, throat, or wounds, and are often used for high-volume testing for pathogens such as Streptococcus, Influenza, and COVID-19. These specimens are essential for microbiology and molecular labs, where nucleic acid amplification techniques like Polymerase Chain Reaction (PCR) are used to detect the genetic material of infectious agents. This rapid, high-throughput testing capability ensures that swabs remain a consistently high-volume specimen type in modern clinical practice.