How to Interpret Microbiology Results – Serology and Virology
Serology is the investigation of a component of blood i.e. serum, to look for evidence of infection, past infection, immunity to infection or susceptibility to infection. Bacteriology looks for a living microorganism whereas serology is not reliant on the microorganism being alive.
The reasons for sending samples to a serology or molecular laboratory are:
In general, there are three types of serology report:
• Antigen detection
- Either molecules from infected cells or fragments of infecting microorganisms
- Detects acute infection
- Cheap, usually a rapid result on the same day as sample received
• Antibody detection
- Indicating the individual’s response to infection
- IgM indicates acute or recent infection
- IgG indicates past infection or immunity
- Cheap, usually a rapid result on the same day as sample received
• Molecular detection of nucleic acid or Polymerase Chain Reaction (PCR)
- Detects microorganism genes by multiplying undetectable amounts of DNA or RNA to a level that can be detected
- Usually used to detect acute infection e.g. Enterovirus PCR in CSF, but can also detect past infection that has reactivated e.g. CMV in HIV positive patients
- Can be affected by contamination as small amounts of microorganism genes can give positive results if they get in to the sample after it has been taken
- Expensive and requires specialist laboratory staff
In reality ALL samples for the diagnosis of infection are sent to the Microbiology Laboratory for processing. The laboratory decides, depending on sample type and clinical details, where best to process the sample e.g. bacteriology, serology, virology, parasitology or mycology (fungi). For details on which test, sample type, container and minimum volume required (see content in the book, Microbiology Nuts & Bolts)
The reasons for sending samples to a serology or molecular laboratory are:
- The organism cannot be cultured e.g. a virus or the non-culturable bacteria e.g. Mycoplasma sp., Chlamydia sp. or Treponema pallidum
- The patient may be on an antibiotic that prevents the microorganism from being cultured e.g. patient with meningitis is correctly given Benzylpenicillin by the GP before admission into hospital, which will stop N. meningitidis from growing but PCR will still detect the bacterium
- To assess the risk of a patient acquiring an infection after exposure to the infectious microorganism e.g. testing for Varicella Zoster Virus antibody in a pregnant woman exposed to Chicken Pox
- To assess whether a patient has had an infection in the past or been immunised against that infection e.g. a patient exposed to blood contaminated with Hepatitis B Virus has evidence of antibodies against the virus and so cannot acquire it from this needlestick injury
- To detect a microorganism that might be too small to see on microscopy e.g. viruses
In general, there are three types of serology report:
• Antigen detection
- Either molecules from infected cells or fragments of infecting microorganisms
- Detects acute infection
- Cheap, usually a rapid result on the same day as sample received
• Antibody detection
- Indicating the individual’s response to infection
- IgM indicates acute or recent infection
- IgG indicates past infection or immunity
- Cheap, usually a rapid result on the same day as sample received
• Molecular detection of nucleic acid or Polymerase Chain Reaction (PCR)
- Detects microorganism genes by multiplying undetectable amounts of DNA or RNA to a level that can be detected
- Usually used to detect acute infection e.g. Enterovirus PCR in CSF, but can also detect past infection that has reactivated e.g. CMV in HIV positive patients
- Can be affected by contamination as small amounts of microorganism genes can give positive results if they get in to the sample after it has been taken
- Expensive and requires specialist laboratory staff
In reality ALL samples for the diagnosis of infection are sent to the Microbiology Laboratory for processing. The laboratory decides, depending on sample type and clinical details, where best to process the sample e.g. bacteriology, serology, virology, parasitology or mycology (fungi). For details on which test, sample type, container and minimum volume required (see content in the book, Microbiology Nuts & Bolts)
Topics in Microbiology:
All these topics are covered in the book...Ready to buy your copy? Click here to buy your copy of "Microbiology Nuts & Bolts" Its updated and amazingly only slightly larger considering its got 1/3 more in it! (11cmx18cmx2.5cm).
- How to Take Microbiology Specimens
- Why Bother Completing Request Forms?
- What is Relevant Information for a Request Form?
- Considerations When Contacting a Microbiologist for Advice
- A to Z of Microbiology Tests by Microorganism or Condition
- A to Z of Microbiology Tests by Specimen Type
- Microbiology Results (by Specimen Type)
- How to Interpret Microbiology Results - Bacteriology
- Examples of Bacteriology Requests, Results and Interpretations
- Why Can’t I Do Every Test?
- Examples of Pre and Post-test Probability Results and Interpretations
- How to Use Pre-test Probability, Likelihood Ratios and Post-test Probabilities in the Clinical Setting
- Basic Bacterial Identification by Microscopy
- Basic Bacterial Identification
- Table of Bacterial Causes of Infection
- How to Interpret Microbiology Results – Serology and Virology
- Examples of Serology / Virology Requests, Results and Interpretations
- Notifiable Infectious Diseases in the UK
All these topics are covered in the book...Ready to buy your copy? Click here to buy your copy of "Microbiology Nuts & Bolts" Its updated and amazingly only slightly larger considering its got 1/3 more in it! (11cmx18cmx2.5cm).
