Diagnosis

Chapter 20

Empirical Therapy

Medical treatment given based on experience and a clinical “educated guess”

• Medication is not specific because the clinician does not know the specific type of pathogen being targeted

Classification

Placing organisms in groups of related species

• Lists of characteristics of known organisms

Identification

Matching characteristics of an “unknown” organism to lists of known organisms

Restriction Fragment Length Polymorphism “RFLP” Analysis

Molecular technique that identifies variations in DNA sequences where DNA is digested with restriction enzymes, run on a gel, and stained with fluorescent or radioactive probe

• Restriction enzymes cut DNA at specific sites

Polymerase Chain Reaction (PCR)

Widely used molecular method that is used to create many copies of a specific DNA sequence

• DNA primers made for specific pathogens → multiple sets of DNA primers can identify individual genes from a pathogen for more specific typing

• Useful for pathogens that are hard to grow or slow to grow

qRT-PCR

Molecular biology technique used to detect and quantify RNA

• Combines reverse transcription (RNA to cDNA) with quantitative PCR to detect cDNA in real-time

Enzyme-Linked Immunosorbent Assay (ELISA)

Biochemical technique used to detect and quantify specific molecules, such as proteins, antibodies, or antigens

• Relies on highly specific antibody-antigen interactions and a reporter enzyme to produce a measurable signal

Direct Assay

Type of immunoassay that uses an enzyme-labeled primary antibody to directly detect and quantify a specific antigen or antibody

• Antigen immobilized onto a plate and then enzyme-labeled antibody binds to it → enzyme reacts with substrate → measurable signal

Indirect Assay

Immunoassay technique where a primary antibody binds to an antigen immobilized onto a plate, and then a secondary antibody labeled with an enzyme binds to the primary antibody, amplifying signal for detection

Capture Assay

Immunoassay technique where an immobilized antibody is bound to a target antigen in a sample, then a secondary antibody labeled is added and binds to a different site on the antigen, creating a “sandwich” complex

Fluorescent Antibody Staining

A technique where antibodies tagged with fluorophores are used to visualized specific targets (antigens) in biological samples

Sensitivity

Refers to how small of a sample a test can detect

Specificity

Refers to how well a test can distinguish positives and negatives

Point of Care “POC” Laboratory Tests

Diagnostic tests performed at or near the site of patient care, often by a non-laboratory personnel

• Salvages the length of time it typically takes for a patient to get their results back

• Good test → high specificity and high sensitivity

Immunochromatographic Assays (ICT)

Many commercial point of care tests involve these → rapid and simple diagnostic technique used to detect the presence or absence of a specific target analyte in a sample