Diagnosing Infections Flashcards
What is required to diagnose an infection?
Demonstrate organism, isolate organism, demonstrate a serological response
How do you demonstrate an organism?
Either by microscopy, or by detecting specific components such as antigens, nucleic acids, toxins etc.
What is a latex agglutination test?
A latex agglutination test is a test to see if antigens are present. In the test, a sample is mixed with latex beads covered with antibodies. If the antigen is present it will bind to the antibodies and cause the latex beads to clump.
What is a solid phase assay test?
A solid phase assay test is a test to see if antigens are present. Antigens from the sample are attached to a surface and then a specific antibody which is tagged with a label is added which can bind to the antigen. Rather than tagging the patients serum can use an anti-human antibody that is pre tagged and will bind to the human antibodies Fc region.
What is a capture assay test?
A capture assay test is a test to see if antigens are present. Antibodies are bound to a surface, then the sample with the antigens is added, then an antibody that is tagged with a label is added.
What is a nucleic acid detection test?
Tests to see if an organism is present by detecting a known nucleic acid sequence. This is done using DNA hybridisation and PCR using a probe with a label.
What is an intact cell mass spectrometry test?
Tests to see if an organism is present by detecting unique biomarkers
What are the three different sites which are used to isolate the organism?
A sterile site which usually has no natural microbiota e.g. the CSF, a site with lots of normal microbiota e.g. the gut or a sterile site abutting site with microbiotic e.g. the lungs and respiratory tract
What further tests are done with isolating the organism?
biochemical tests, DNA analysis, antimicrobial susceptibility
How do you demonstrate a serological response?
Detect a specific immune response to an organism
What test is done to demonstrate a serological response?
Solid phase assay - with an known antigen to test whether antibodies are present, western blot -
How do you tell whether the antibodies present are because of a recent infection or a past infection?
Can either look for a 4 fold rising titre with 2 samples separated by 7-10 days, or can look for specific IgM antibodies
