Clinical Specimen Collection, Processing and Reporting
Introduction
This domain covers the pre-analytical phase: correct specimen selection, timing, collection, transport, labelling, rejection, processing, and reporting. The exam tests why specimen quality often determines result quality.
Core rules
- Collect before starting antibiotics whenever possible, and at the correct time for the suspected infection.
- Use the correct container and transport medium; blood cultures need defined sets and volume, urine needs a clean-catch midstream sample, and CSF must be transported promptly without delay.
- Label the specimen at the bedside with patient identity, site, date, and time; an unlabelled or mislabelled specimen should be rejected.
- Transport at the specified temperature and within the specified time; delay can overgrow contaminants and kill fastidious pathogens.
- Report critical results by phone and document the read-back.
Worked example
A clean-catch urine sample grows 10^5 CFU/mL of a single lactose-fermenting organism with pyuria. This supports urinary tract infection and warrants identification and susceptibility testing. If the same sample shows three mixed colony types with squamous epithelial cells, it suggests contamination; a repeat specimen is more useful than reporting a meaningless mix.
Traps
Do not accept a sputum sample that is mostly saliva for bacterial culture; quality matters. Do not delay CSF transport. Do not assume a positive culture always means infection; contamination and colonisation are common. A rejected specimen is not a laboratory failure; it protects patient care.