A medical laboratory or clinical laboratory is a laboratory where clinical pathology tests are carried out on clinical specimens to obtain information about the health of a patient to aid in diagnosis, treatment, and prevention of disease.[1] Clinical Medical laboratories are an example of applied science, as opposed to research laboratories that focus on basic science, such as found in some academic institutions.

Medical laboratories vary in size and complexity and so offer a variety of testing services. More comprehensive services can be found in acute-care hospitals and medical centers, where 70% of clinical decisions are based on laboratory testing. Doctors’ offices and clinics, as well as skilled nursing and long-term care facilities, may have laboratories that provide more basic testing services. Commercial medical laboratories operate as independent businesses and provide testing that is otherwise not provided in other settings due to low test volume or complexity.

In hospitals and other patient-care settings, laboratory medicine is provided by the Department of Pathology, and generally divided into two sections, each of which will be subdivided into multiple specialty areas. The two sections are:

Anatomic pathology: areas included here are histopathology, cytopathology, and electron microscopy.

Clinical pathology, which typically includes the following areas:

Clinical Microbiology: This encompasses several different sciences, including bacteriology, virology, parasitology, immunology, and mycology.

Clinical Chemistry: This area typically includes automated analysis of blood specimens, including tests related to enzymology, toxicology and endocrinology.

Hematology: This area includes automated and manual analysis of blood cells. It also often includes coagulation.

Blood Bank involves the testing of blood specimens in order to provide blood transfusion and related services.

Molecular diagnostics DNA testing may be done here, along with a subspecialty known as cytogenetics.

Reproductive biology testing is available in some laboratories, including Semen analysis, Sperm bank and assisted reproductive technology.

Layouts of clinical laboratories in health institutions vary greatly from one facility to another. For instance, some health facilities have a single laboratory for the microbiology section, while others have a separate lab for each specialty area.

Laboratory equipment for hematology (black analyser) and urinalysis (left of the open centrifuge).

The following is an example of a typical breakdown of the responsibilities of each area:

• Microbiology includes culturing of clinical specimens, including feces, urine, blood, sputum, cerebrospinal fluid, and synovial fluid, as well as possible infected tissue. The work here is mainly concerned with cultures, to look for suspected pathogens which, if found, are further identified based on biochemical tests. Also, sensitivity testing is carried out to determine whether the pathogen is sensitive or resistant to a suggested medicine. Results are reported with the identified organism(s) and the type and amount of drug(s) that should be prescribed for the patient.
• Parasitology is where specimens are examined for parasites. For example, fecal samples may be examined for evidence of intestinal parasites such as tapeworms or hookworms.
• Virology is concerned with identification of viruses in specimens such as blood, urine, and cerebrospinal fluid.
• Hematology analyzes whole blood specimens to perform full blood counts, and includes the examination of Blood films. Other specialized tests include cell counts on various bodily fluids.
• Coagulation testing determines various blood clotting times, coagulation factors, and platelet function.
• Clinical Biochemistry commonly performs dozens of different tests on serum or plasma. These tests, mostly automated, includes quantitative testing for a wide array of substances, such as lipids, blood sugar, enzymes, and hormones.
• Toxicology is mainly focused on testing for pharmaceutical and recreational drugs. Urine and blood samples are the common specimens.
• Immunology/Serology uses the process of antigen-antibody interaction as a diagnostic tool. Compatibility of transplanted organs may also be determined with these methods.
• Immunohematology, or Blood bank determines blood groups, and performs compatibility testing on donor blood and recipients. It also prepares blood components, derivatives, and products for transfusion. This area determines a patient's blood type and Rh status, checks for antibodies to common antigens found on red blood cells, and cross matches units that are negative for the antigen.
• Urinalysis tests urine for many analytes, including microscopically. If more precise quantification of urine chemicals is required, the specimen is processed in the clinical biochemistry lab.
• Histopathology processes solid tissue removed from the body (biopsies) for evaluation at the microscopic level.
• Cytopathology examines smears of cells from all over the body (such as from the cervix) for evidence of inflammation, cancer, and other conditions.
• Molecular diagnostics includes specialized tests involving DNA analysis.
• Cytogenetics involves using blood and other cells to produce a DNA karyotype. This can be helpful in cases of prenatal diagnosis (e.g. Down's syndrome) as well as in some cancers which can be identified by the presence of abnormal chromosomes.
• Surgical pathology examines organs, limbs, tumors, fetuses, and other tissues biopsied in surgery such as breast mastectomies.