Clinical Laboratory Procedures
Clinical Laboratory Procedures
This domain tests sample collection and handling, hematology, chemistry, urinalysis, cytology, and parasitology. Many questions hinge on whether a result is real or an artifact.
Core rules
- CBC components: PCV/hematocrit, total protein by refractometer, blood smear evaluation, and a platelet estimate. Roughly one platelet per oil-immersion field corresponds to about 15,000/µL.
- Chemistry: BUN and creatinine reflect renal function; ALT and ALP reflect hepatobiliary injury; albumin and glucose are commonly altered by other disease.
- Urinalysis: specific gravity by refractometer, dipstick chemistry, and sediment examination. Cystocentesis is preferred when culture is planned.
- Fecal flotation concentrates parasite eggs; a direct smear is far less sensitive.
- Tube choice: EDTA (lavender) for CBC, serum separator or heparin for chemistry; hemolysis and lipemia falsely alter many results.
Worked example
A well-hydrated dog has PCV 45% and total protein 8.6 g/dL. The PCV is normal, so this is not anemia; the elevated protein suggests dehydration or hyperproteinemia. If the sample sat in an EDTA tube for 12 hours, repeat on a fresh sample before treating.
Traps
- Reading a lipemic sample's chemistry as valid without noting the interference.
- Calling a low platelet count from a clumped sample true thrombocytopenia.
- Sampling from the same limb used for fluid administration.
- Forgetting that EDTA tubes must be filled to the marked line.