This page explains laboratory work in general terms. It is not medical advice and cannot interpret anyone's test results — that belongs with a doctor or care team.
A hospital laboratory contains several kinds of scientific work. Some benches count cells; others measure dissolved chemicals, grow microorganisms or examine the structure of tissue. The department names describe those different questions. The division called clinical chemistry focuses on substances in body fluids and tissues, while hematology includes the laboratory study of blood and its components. A job title and a department name therefore describe different things: a laboratory scientist may work in a particular testing area.
Clinical chemistry: measuring substances in fluids
Clinical chemistry draws on biology, chemistry and instrument-based measurement. Blood and urine are common specimens, with serum and plasma important in blood testing. Automated instruments can handle specimen movement and perform measurement techniques such as photometry and spectrometry; some specimens need processing before they reach that stage, as the clinical chemistry reference explains. The laboratory worker needs to understand both the material being tested and the analytical process.
A panel groups related measurements. The MedlinePlus basic metabolic panel guide lists glucose, calcium, electrolytes and kidney-related waste products. The comprehensive metabolic panel guide adds proteins, liver-associated enzymes and bilirubin. For someone exploring careers, the useful distinction is between measuring a cell and measuring a substance in the fluid around cells. The fuller explanation of blood counts, chemistry panels and hormone measurements follows those categories through the laboratory.
Some chemistry measurements support urgent care. MedlinePlus describes troponin testing as commonly performed in a hospital emergency room alongside other heart tests; the laboratory measures a protein in blood. The National Cancer Institute explains tumor markers as information normally considered with other tests rather than as a stand-alone cancer diagnosis.
The specialty includes manual work as well as automated testing. The clinical chemistry specialty overview separates routine chemistry from special chemistry, which includes electrophoresis and manual methods, and identifies clinical endocrinology as the hormone-focused area. Specimen preparation is another bench responsibility: centrifugation separates denser cells from the fluid portion used for many chemistry measurements. An instrument may incorporate that preparation into its operation, or the sample may need processing before analysis. The worker therefore handles both a physical separation and a chemical measurement, depending on the method.
Hematology and coagulation: cells and clotting
A complete blood count, or CBC, reports the number and size of blood cells along with measurements such as hemoglobin and hematocrit. Red cells carry oxygen; white cells take part in defense against infection and disease; platelets help blood clot. MedlinePlus describes the CBC as a group of measurements rather than a single all-purpose health answer. The work brings cell counting together with an understanding of cell types and blood composition.
A differential separates the white-cell measurement into its constituent types. The MedlinePlus blood differential guide explains that measuring each type differs from measuring the total white-cell count. Coagulation concerns the formation of a clot, involving platelets and proteins that form fibrin, as the coagulation reference describes. Cell counts and clotting studies examine related material but answer different laboratory questions.
The CBC’s component names describe different properties. MedlinePlus’s explanation of CBC measurements defines hemoglobin as an iron-containing protein that carries oxygen, hematocrit as the portion of whole blood made up of red cells, and mean corpuscular volume as average red-cell size. A differential further distinguishes neutrophils, lymphocytes, monocytes, eosinophils and basophils. The white-cell differential description explains that the laboratory can report their amounts or proportions. Lymphocytes include B cells and T cells; eosinophils participate in responses to parasites and allergies. These are descriptions of cell populations, without assigning a diagnosis to a count.
Medical microbiology: looking for microorganisms
Medical microbiology studies infectious organisms and their characteristics. Its scope includes bacteria, fungi, parasites and viruses, as the medical microbiology reference explains. The bench work is therefore broader than growing bacteria in dishes. The method depends on the organism and on the specimen that reaches the laboratory.
A Gram stain makes some bacterial features visible under a microscope. A laboratory professional prepares a slide, applies the stain and examines the color and shape of organisms. The MedlinePlus Gram stain guide notes that the findings may narrow the possibilities without establishing an exact bacterial identity.
A culture allows organisms in a specimen to grow in a suitable medium so they can be examined. The MedlinePlus bacterial culture guide explains that growth is needed to obtain enough cells for identification. Susceptibility work then examines the response of the organism to antibiotics in the laboratory, as the antibiotic sensitivity guide describes. These are different stages: observing appearance, establishing identity and assessing a laboratory response.
The stain’s color develops through a chemical sequence. MedlinePlus’s description of staining explains that solvent is applied after purple coloring; bacteria that retain the purple appearance are described as Gram-positive, while those appearing pink or red are Gram-negative. The microscope examination also records shape, such as round cocci or rod-shaped bacilli. Color and shape are distinct observations. The source also notes that a Gram stain cannot detect a virus, so the method has a defined scope.
Immunology, serology and urinalysis
Serology studies antibodies in serum and other body fluids. Tests can look for antibodies or antigens, using methods such as ELISA or agglutination, according to the serology reference . An antibody is a protein that recognizes particular molecular features; an antigen is material that can bind a specific antibody. Those definitions in the antibody reference and antigen reference explain why binding reactions can become laboratory tools.
Urinalysis combines observations that operate at different scales. Staff may assess the sample's physical appearance, use chemical test strips and examine material under a microscope. The urinalysis reference describes cells, casts, crystals and organisms among the structures that microscopy can identify. A sample's visible appearance, chemical composition and microscopic contents are separate forms of evidence.
For urine microscopy, centrifugation can concentrate solid material before a drop is placed beneath a coverslip. The urinalysis microscopy description distinguishes examination of concentrated sediment from counting cells in an unconcentrated sample using a counting chamber. Laboratories may use ordinary light microscopy, phase-contrast microscopy or automated systems based on flow cytometry or pattern recognition. The automated systems described in the reference recognize common elements more reliably than unusual cells, casts or crystals. Staining can make components easier to distinguish. Separately, reagent pads on a test strip change color through chemical reactions with sample components.
A department map
| Department | What it examines | Examples of tests |
|---|---|---|
| Clinical chemistry | Substances dissolved in body fluids | Metabolic panels measuring glucose, electrolytes and waste products; MedlinePlus BMP. |
| Hematology | Blood cells and their characteristics | Complete blood count and differential; MedlinePlus CBC. |
| Microbiology | Microorganisms in appropriate specimens | Staining and bacterial culture; MedlinePlus culture guide. |
| Serology | Antibodies or antigens in a sample | ELISA and agglutination methods; serology reference. |
| Urinalysis | Physical, chemical and microscopic features of urine | Test-strip chemistry and microscopy; urinalysis reference. |
Other areas, and testing near care
The blood bank examines blood groups and compatibility. Cytology and histology examine cells and tissue, while molecular diagnostics examines molecular material such as DNA. These areas deserve their own explanations because the preparations and the questions differ from routine chemistry or cell counting.
Testing near care can use handheld instruments, portable equipment or small bench analyzers. The point-of-care technology overview includes blood-gas and electrolyte measurements, coagulation tests and cardiac-marker measurements as examples. Connecting devices with electronic medical records allows results to be shared with care providers. The reference specifically distinguishes the location of testing from the complexity of the method: a test performed near care is not automatically a simple or waived test. Staff still need to understand the procedure and its requirements.
Not every measurement happens in the main laboratory. Point-of-care testing means testing at or near the place care is provided. Its examples include glucose measurement, urine test strips and some infectious-disease tests. A hospital's testing work therefore includes both centralized departments and methods used nearer the point of care.