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Cytogenetics

Specimen & Test Requests

The pre-analytical phase of testing is the primary source of laboratory error. In Clinical Cytogenetics, where specimen recollection is often invasive or impossible, the verification of patient identity and the strategic triage of test requests are critical safety checkpoints. The laboratory scientist acts as the gatekeeper, ensuring that the clinical intent aligns with the laboratory procedure and that resources are allocated to the most urgent cases

Verify Patient Information & Test Orders

Regulatory standards (CLIA/CAP) mandate strict adherence to patient identification and requisition review to prevent “wrong patient, wrong test” errors

  • Patient Identification (The Two-Identifier Rule)
    • Every specimen and requisition must possess two unique identifiers (e.g., Full Name + Date of Birth, or Name + MRN)
    • The Match: The identifiers on the tube label must match the requisition exactly. Discrepancies (spelling, transposed dates) must be resolved before processing
    • Unacceptable Identifiers: Non-unique data such as room number or physician name cannot be used for verification
  • Requisition Review
    • Biological Sex: Essential for interpreting sex chromosomes. A 46,XY result is normal for a male but pathological (or a mix-up) for a female
    • Clinical Indication: The laboratory scientist must verify that the ordered test matches the diagnosis. For example, a request for “Chromosome Analysis” on blood for a leukemia patient requires an unstimulated culture (to catch blasts), whereas the same order for infertility requires a stimulated culture (PHA to grow T-cells). Processing it incorrectly renders the test useless
  • Handling Discrepancies
    • Minor (Clerical): Can often be resolved by phone confirmation with the ordering clinic
    • Major (Identity Mismatch): Usually mandates specimen rejection
    • Irretrievable Specimens: For precious samples (amniotic fluid, marrow), an “Exception Protocol” may be used, requiring the physician to physically identify the specimen and sign a liability waiver

Assign Test Priority (Triage)

Because cytogenetic cultures take days to weeks to grow, the laboratory must prioritize processing based on the immediate medical necessity of the result

  • STAT / Emergency (Immediate Clinical Impact)
    • Newborns with Anomalies: Ambiguous genitalia or life-threatening defects (Trisomy 13/18) where the result determines palliative care vs. surgery
    • Acute Promyelocytic Leukemia (APL): Diagnosis of t(15;17) dictates immediate, life-saving ATRA therapy. Often handled via STAT FISH
    • Late Gestational Age: Prenatal samples nearing the legal termination limit or delivery date
  • Urgent (Diagnosis Pending)
    • New Acute Leukemias (AML/ALL): Results determine the chemotherapy regimen and risk stratification
    • Routine Prenatal (Amnio/CVS): Prioritized to minimize parental anxiety and allow decision-making time
  • Routine (Long-term Management)
    • Constitutional Studies: Developmental delay, autism, or dysmorphic features (often done via Microarray)
    • Infertility/Recurrent Loss: Balanced translocation workups for future family planning
    • Solid Tumors: Often inherently slow-growing; results used for subtype confirmation or long-term prognosis
  • Operational Triage Strategies
    • Preliminary Reports: Issuing a “Prelim” result (e.g., “Positive for t(9;22)”) immediately upon finding the abnormality, allowing treatment to start while the full analysis completes
    • Short Harvests: Harvesting STAT cultures “early” (e.g., 24 hours) to catch fast-dividing clones, accepting a potentially lower mitotic index for the sake of speed