Pre-Anaesthetic Bloodwork That Does Not Fit the Dog
A 9-year-old male Doberman is in for pre-anaesthetic bloodwork before a dental procedure. At 10:20 a technician draws 3 mL from the left cephalic vein with a 22-gauge needle and a 3 mL syringe, then transfers it into a lavender-top EDTA tube and a plain red-top tube. The EDTA tube is shaken vigorously to mix it. Both tubes sit in a rack on the treatment-room counter because the chemistry analyser is tied up with an emergency. The red-top tube is centrifuged at 15:20 and run immediately; the EDTA sample is run for a CBC at the same time - about five hours after collection. Results: potassium 7.9 mmol/L, glucose 42 mg/dL, PCV 58%, platelets 38,000/µL with clumps visible on the film, total protein 6.9 g/dL, BUN 18 mg/dL, creatinine 1.0 mg/dL. The dog is bright and alert, drank water in the lobby, urinated normally on the walk, and ate breakfast at 06:00.
1. Which of these results would you trust and which would you challenge? Name the specific pre-analytical error behind each suspect value and the mechanism.
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Challenge these:
- Potassium 7.9 mmol/L. A dog with a true potassium near 8 is usually bradycardic, weak and unwell; this dog is bright and drinking. Vigorous shaking of the EDTA tube and a small-gauge needle cause haemolysis, and red cells hold potassium at roughly 20–25 times the plasma concentration, so haemolysis inflates the result. EDTA itself also contains potassium - if any EDTA blood contaminated the chemistry sample, potassium rises and calcium falls.
- Glucose 42 mg/dL. Serum left in contact with cells for five hours without separation continues to glycolysis; red cells consume glucose at roughly 5–10% per hour. A dog that ate at 06:00 should not be at 42 mg/dL. This is in vitro glucose consumption, not hypoglycaemia.
- Platelets 38,000/µL with clumps. Clumping is the commonest cause of a spurious low platelet count; the analyser counts particles, not platelets, and clumps fall outside the counting window. EDTA-dependent platelet clumping is a well-recognised artefact in some dogs.
Trust, with reservations: BUN, creatinine and total protein fit a well-hydrated dog. PCV 58% may be real - Dobermans splenic-contract with excitement - or may reflect five hours of red-cell settling; it needs repeating on a fresh, well-mixed sample.
2. The veterinarian wants reliable results before anaesthesia. Describe how you would recollect and handle the samples, and how you would settle the platelet question.
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Recollect calmly and deliberately. Let the dog settle in a quiet area rather than wrestling a Doberman in a busy treatment room; excitement alone shifts PCV. Use a 22-gauge needle on a 3 mL syringe, fill tubes to their marked volume (an under-filled EDTA tube concentrates EDTA and distorts cells), mix by gentle inversion 8–10 times - never shake - and label at the bedside.
Handle the chemistry sample properly: allow the red-top to clot at room temperature for 20–30 minutes, then centrifuge within an hour of collection, separate the serum and run it promptly. If the analyser is busy, that is an argument for a lithium heparin tube run as plasma, not for leaving blood sitting on cells for five hours. Note the collection time and the run time on the request so the next person can see the interval.
Settle the platelets: examine a stained blood film at low power for clumps, and estimate - roughly one platelet per oil-immersion field per 15,000/µL. If clumping is confirmed, a fresh sample in citrate or heparin often gives a countable result; alternatively a manual count on the fresh EDTA sample. The clumped value should not be reported or acted on as if it were a real thrombocytopenia.
3. Ten minutes later the veterinarian, who has not yet seen the sample handling notes, says she is going to call the owner about 'possible kidney failure and a bleeding disorder'. What do you do?
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Speak up immediately and specifically - this is the point of the whole exercise. Tell her the sample was collected at 10:20 and not separated or run until 15:20, that the EDTA tube was shaken hard, and that in a bright, drinking dog the potassium and glucose are most likely artefactual with a BUN of 18 and creatinine of 1.0 that do not support kidney failure. Offer the film findings and the plan for a fresh sample.
Do it as information, not as a challenge to her authority: 'Before you call - can I show you the collection times? I think these numbers are pre-analytical.' She makes the clinical decision; your job is to make sure she has the facts.
Document: collection time, handler, tube types, the interval before processing, the shaking and the delay, who was notified and when, and what was recollected. Never alter the original results - annotate them as suspect and re-run. If the owner is called before a repeat, the conversation should be framed as 'we need a repeat test' rather than a diagnosis, which protects the client relationship and the practice.