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Microbiology

Prioritization & Rejection

A wide variety of specimens are received in the clinical microbiology laboratory. Specimen prioritization is how we triage these samples, ensuring that the most critical ones get processed first to help patients who need answers urgently. Specimen rejection criteria are the rules we follow to identify specimens that are too compromised to give us reliable results. By prioritizing correctly and rejecting poor-quality samples, we ensure accurate and timely diagnoses, leading to better patient care

Specimen Prioritization: Triage in the Lab

  • The Need for Prioritization
    • In a clinical microbiology lab, the volume and variety of specimens can be high. Not all specimens require the same immediate attention
    • Prioritization ensures that specimens from critical cases or those with time-sensitive diagnostic implications are processed first. This can directly impact patient care and outcomes
  • Factors Influencing Prioritization
    • Specimen Source
      • Sterile Body Sites: Specimens from normally sterile sites (e.g., CSF, blood, sterile body fluids) are almost always high priority. The presence of any organism may indicate a serious infection
      • Non-Sterile Sites: Specimens from sites with normal flora (e.g., sputum, wound, stool) may be lower priority unless specific pathogens are suspected or the patient is immunocompromised
    • Patient Status
      • Immunocompromised Patients: Specimens from patients with weakened immune systems (e.g., transplant recipients, HIV/AIDS patients, chemotherapy patients) are often prioritized due to increased susceptibility to opportunistic infections
      • Critically Ill Patients: Specimens from patients in the ICU or those with severe infections (e.g., sepsis, meningitis) are high priority
    • Physician Request/Clinical Information
      • “STAT” Requests: Specimens specifically marked as “STAT” (urgent) require immediate processing
      • Relevant Clinical History: Information provided by the physician (e.g., suspected organism, recent travel, antibiotic use) can influence prioritization. For example, a request for “rule out malaria” on a blood sample would be high priority
    • Specimen Type
      • Certain specimen types inherently carry a higher risk or diagnostic value. For example, a CSF sample is almost always higher priority than a routine urine culture
  • Common Prioritization Levels (Examples)
    • These may vary by lab, but common categories include:
      • STAT/Critical: Process immediately (e.g., CSF, blood cultures from septic patients)
      • High Priority: Process within a few hours (e.g., sterile body fluids, respiratory samples from ventilated patients)
      • Routine: Process within the normal daily workflow
      • Batch: Processed together at a specific time (e.g., certain surveillance cultures)

Specimen Rejection Criteria: Ensuring Quality Results

  • The Importance of Rejection Criteria
    • Submitting a poor-quality specimen will result in poor and unreliable results, leading to:
      • Misdiagnosis
      • Delayed or inappropriate treatment
      • Wasted resources (time, labor, materials)
      • Inaccurate epidemiological data
    • Clear rejection criteria protect the integrity of laboratory testing and ensure accurate patient care
  • Common Rejection Criteria
    • Improper Labeling
      • Unlabeled Specimen: Any specimen without a label is unacceptable
      • Mislabeled Specimen: Information on the label does not match the requisition form (e.g., patient name, date of birth, specimen source)
      • Unreadable Label: Illegible handwriting or damaged labels that prevent accurate identification
    • Inappropriate Collection Container/Transport
      • Wrong Collection Device: Using an incorrect container for the specimen type (e.g., using a non-sterile container for a sterile fluid)
      • Expired Collection Device: Using collection kits or transport media past their expiration date
      • Improper Transport Media: Specimen not submitted in the appropriate transport media to preserve viability
    • Insufficient Quantity (QNS - Quantity Not Sufficient)
      • Too little specimen to perform the requested tests. Minimum volumes are usually specified in the lab’s standard operating procedures
    • Prolonged Transport Time/Improper Transport Conditions
      • Delayed Transport: Specimen held for too long before reaching the lab, potentially leading to organism death or overgrowth of contaminants
      • Incorrect Temperature: Specimen not transported at the required temperature (e.g., not refrigerated when required)
    • Leaking or Contaminated Container
      • Specimen container is leaking, posing a biohazard risk
      • External contamination of the container, potentially compromising the specimen’s sterility
    • Duplicate Specimens
      • Multiple specimens of the same type collected from the same patient on the same day, unless specifically indicated (e.g., multiple blood cultures)
    • Specimen Integrity Compromised
      • Dried-Out Specimen: Specimen has dried out due to improper storage or transport
      • Presence of Interfering Substances: Specimen contains substances that interfere with testing (e.g., formalin in a specimen intended for culture)
    • Inappropriate Specimen Type for the Test Requested
      • Requesting a test on a specimen type that is not suitable for that test (e.g., requesting a sputum culture on a saliva sample)
    • Contaminated Specimen
      • Evidence of gross contamination (e.g., blood in a urine sample when it should be sterile)
      • Specimens with obvious contamination may be rejected to prevent false-positive results
    • Request Form Issues
      • Missing information on the requisition form (e.g., patient demographics, date/time of collection, test requested)
      • Discrepancies between the requisition form and the specimen label
  • The Rejection Process
    1. Documentation: The reason for rejection must be clearly documented in the laboratory information system (LIS) or on a rejection form
    2. Notification: The ordering physician or appropriate healthcare personnel must be notified of the rejection
    3. Repeat Collection (if possible): If the specimen is rejected due to a correctable error (e.g., improper labeling), a new specimen should be requested
    4. Exceptions/Consultation: In some cases, the laboratory director or a senior technologist may make an exception and process a suboptimal specimen, especially if it is difficult to obtain a new specimen (e.g., CSF) or if the patient’s condition is critical. This decision should be documented

Key Considerations and Best Practices

  • Clear and Accessible SOPs: The laboratory should have clearly written and readily accessible Standard Operating Procedures (SOPs) outlining specimen prioritization and rejection criteria
  • Training: All laboratory personnel must be thoroughly trained on proper specimen handling, prioritization, and rejection procedures
  • Communication: Effective communication between the lab, healthcare providers, and phlebotomists is essential to minimize errors and ensure timely collection of appropriate specimens
  • Regular Review: Rejection criteria and prioritization protocols should be reviewed regularly and updated as needed to reflect changes in testing methodologies, clinical guidelines, and regulatory requirements
  • Documentation of all Corrective Actions: Every action should be documented

Key Terms

  • Aliquoting: The process of dividing a single specimen into multiple smaller portions for separate testing or storage
  • Aseptic Technique: A set of practices and procedures performed under carefully controlled conditions with the goal of minimizing contamination by pathogens
  • Contamination: The introduction of unwanted microorganisms into a specimen, culture, or sterile environment, potentially leading to inaccurate results or infection
  • Inoculation: The process of introducing a microorganism into a culture medium to initiate growth and propagation for identification and testing
  • Nosocomial Infection: An infection acquired in a hospital or other healthcare facility; also known as a healthcare-associated infection (HAI)
  • Pathogen: A microorganism (e.g., bacterium, virus, fungus, parasite) capable of causing disease in a susceptible host
  • Requisition: A formal request for laboratory testing, typically including patient information, specimen details, and the specific tests to be performed
  • Sterile: Free from all living microorganisms, including bacteria, viruses, fungi, and spores
  • Supernatant: The liquid portion of a sample that remains after a solid (e.g., cells, debris) has settled or been centrifuged
  • Viability: The ability of a microorganism to survive, reproduce, and maintain its metabolic activity