Laboratory Procedures and Diagnostic Imaging
This domain tests specimen selection and handling, quality control, and the imaging skills that produce diagnostic rather than merely acceptable studies.
Sample handling
- Match tube to test: EDTA (lavender) for hematology, citrate (blue) for coagulation and filled to maintain the 9:1 ratio, serum separator or clot activator for chemistry, heparin (green) for select assays, oxalate-fluoride (gray) for glucose.
- Hemolysis falsely raises potassium, AST and LDH; lipemia interferes with many chemistry reactions; both should be noted on the report.
- Make blood smears promptly and examine the monolayer near the feathered edge for platelet estimates and cell morphology.
- Urinalysis combines specific gravity by refractometer, chemical dipstick and sediment examination; cystocentesis is preferred when culture is planned.
- Dogs are typed for DEA 1.1 first because it is the most antigenic; crossmatch before any transfusion.
Imaging
- Follow ALARA: apron, gloves, thyroid shield, dosimeter, and restraint devices instead of hands in the beam.
- Take orthogonal views. Collimate, position carefully, and label the film or file.
- Contrast studies use barium or iohexol; ultrasound requires clipping and gel for an acoustic window.
Worked example
A cat's CBC reports 40,000 platelets but there is no bleeding and the technician sees clumps in the smear. This is pseudothrombocytopenia from clumping in EDTA. The correct step is to recheck with a fresh sample, often in citrate, and report the estimate rather than a machine count alone.
Traps that cost marks
Underfilled citrate tubes, overfilled EDTA microtainers that dilute the sample, delaying smears until cells distort, hands in the primary beam, and reading a single radiographic view as if it were a complete study.