Microbiology tests
Also known as: infection tests, cultures and swabs
Tests that find the organism causing an infection: growing it on culture, detecting its genes by PCR, its proteins by antigen tests, or the antibodies the body makes against it. Culture also reports which antibiotics work.
- Kind
- Microbiology test
- Categories
- Infectious disease & microbiology
- Specimen
- Venous blood, Sputum, Wound or skin swab, Throat swab, Nose or nasopharyngeal swab, Stool
- Method
- Culture, Microscopy, Antigen detection, Serology (antibody detection), PCR (including RT-PCR and qPCR), Antimicrobial susceptibility testing
What it measures
| Measure | What it tells you |
|---|---|
| Blood cultures | Two bottles from separate sites before antibiotics; growth within 48 hours confirms bloodstream infection and its organism. |
| Swabs and sputum | Throat, wound, genital and sputum samples cultured or tested by PCR. |
| PCR and antigen tests | Fast detection of viruses (COVID-19, influenza) and hard-to-grow bacteria. |
| Serology | Antibodies show past or current infection (hepatitis, HIV, glandular fever) and immunity after vaccination. |
| Stool tests | Bacteria, parasites and C. difficile toxin; faecal immunochemical test screens for bowel cancer. |
Why it is ordered
- Fever with no obvious source, rigors, suspected sepsis
- Pneumonia, urinary infection, wound infection, meningitis
- Diarrhoea lasting more than a few days or after travel
- Screening for HIV, hepatitis and sexually transmitted infections
- Outbreak control and infection prevention (MRSA screening)
How it is done
Samples taken with sterile technique, ideally before antibiotics; results from hours (PCR) to days (culture) or weeks (TB).
Preparation. None for most; clean-catch technique for urine, deep cough for sputum.
Reading the result
| Finding | Usual meaning |
|---|---|
| Two blood cultures grow the same organism | True bacteraemia; find the source and treat for the right duration |
| Skin organism in one bottle only | Probably contamination |
| PCR positive for influenza | Antiviral treatment if early and at risk; isolation |
| Resistant organism | Antibiotic changed to a sensitive agent; infection control alerted |
Reference ranges vary by laboratory, method, age, sex and clinical context; a result is read against the person, not a table.
Limitations
Cultures are negative in a third of sepsis cases, especially after antibiotics; a positive result can mean colonisation rather than infection.
Medicines monitored with this test
Each medicine page cites the official document that names this test in its monitoring plan.
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.