By Elizabeth Youens, BSc BVSc MRCVS

The dog complete blood count (dog CBC) is a widely used tool in animal diagnostics around the world. Annual dog bloodwork for routine health checkups? Get a CBC. Sick pup rushed in? Better get a puppy CBC! Geriatric dog slowing up? Probably needs a CBC! You get the picture. 

Analyzing a complete blood cell count provides invaluable information as part of a diagnostic workup by comparing the patient’s absolute count and cell distribution to normal ranges. However, interpreting canine CBCs is not a one-size-fits-all solution and requires age-specific interpretation, especially as neonates emerge into adult dogs. Learn more how age-specific reference intervals in dogs can help veterinarians provide more accurate diagnoses and care. 

Why do I need a dog CBC and how do I do it?

We use complete blood counts and chemistry data as they provide objective and specific parameters towards patient insights when interpreted alongside a more subjective physical exam. Therefore, we perform these diagnostic tests on a large range of patients: different ages, breeds, sexes, and sizes, but routinely compare all of these differing patients to the same set of normal ranges for red and white blood cells.

The sample requirement for a CBC is usually a small amount of venous blood, usually taken via an accessible peripheral vein, placed into an EDTA tube, and gently inverted to avoid clotting. A successful blood draw in sick puppies can be tricky, but only a small amount of blood is required. A blood smear should always be made concurrently to assess platelet count, cell morphology, and abnormal cells.

How do we interpret a dog CBC?

Interpretation of hematological test results is usually based upon reference intervals, often provided for us by peer reviewed journals, an animal reference laboratory, or veterinary pathologist. If the blood sample is sent to an external laboratory for a complete blood cell count, with accompanying clinical history, a veterinary pathologist interpretation may be provided, but often the results are provided merely in figure format with an accompanying reference interval for each parameter, including absolute count, cell volume, and cell type.

Individual values are considered ‘normal’ if they fall within these ranges, and it is therefore essential that the reference interval used is appropriate for the patient and lab methodology to gain a meaningful and accurate interpretation. Differing ranges for different species is well-known, but the age and breed variances in dog hematology are less considered in the clinical process.

Why can’t we just use normal reference intervals for puppies?

Many reference ranges are constructed using a population of closed-colony adult dogs to gain standard values. However, puppy physiology varies from adult dogs, and it is therefore likely that the blood results for both puppy chemistry and hematology differ from adult levels. A blood sample as part of a diagnostic workup, alongside a physical examination, is only of use if the hematological and biochemical values are accurate. 

This calls into question whether these standardized results are appropriate for diagnostic conclusions about normal ranges for canines of different ages. 

What reference intervals are appropriate for puppies?

The best data that presently exists is via a study by Brenten et al. in 2016, and there has been some robust research from this and previous studies, providing some potential values for a complete blood cell count in young dogs.

The below figures are from Harper et al. (2003) and correlate with a review by Brenten et al. (2016).

Reference intervals: neonate to adult

WBC (10⁹/L)

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RBC (10¹²/L)

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Hemoglobin (g/L)

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HCT (L/L)

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Reference intervals: a summary

Let’s run through a summary of how canine CBCs vary with age.

·  WBC count potentially varies with age. The white blood cell count is at an increased level in very young puppies (3 - 8 weeks) and then gradually decreases with age.

·  In comparison, RBC count, hematocrit and Hb concentration are all lower in young pups and slowly increase until a plateau is reached after around 1 year of age.

·  MCV also shows a gradual decrease as age increases.

How might these values affect interpretation?

Practically speaking, this research is widely applicable to veterinarians providing care to dogs of all ages. Most importantly, considering the canine’s age rather than a potential disease progression while assessing blood results could explain hematological results that are outside of standard dog reference intervals.

·  Care must be taken with interpreting WBC counts in dogs under 1 year of age as values might be higher than expected, falsely indicating infectious diseases such as viral disease or other pathologies.

·  It is normal to see low values for Hb, RBC and HCT in young pups. This may not indicate anemia. Dogs will only reach normal ranges for adult values for these parameters at around 6 - 12 months.

Many studies looking at age differences also noted breed differences in dog hematology and age variances in young dog chemistry, as well as potential sex differences.

What’s the evidence for neonate versus adult canine reference intervals?

A 2003 study (Harper et al., 2003) took a serum sample from both Labrador and Beagle puppies at between 3 - 8 weeks old, 8 - 16 weeks old, 16 weeks - 1+ years and found the above values which show marked differences from adult normal values.

These findings correlate with the Brenten et al. (2016) work on Labrador retrievers and Miniature Schnauzers which sampled puppies at weeks 8, 10, 12, 14, 16, 20, 26, 36 and 52 and found similar variations in red and white blood cells within the first year. These findings are again matched by a South Korean study in 2019 (Yi et al., 2019) looking at Sapsaree pups, which found that RBC count, hematocrit, and hemaglobin are all reduced in the first year of life. 

A 2020 study (Lee et al., 2020) looked at growth hormone, insulin growth factors, glucose levels, and protein concentrations as biomarkers for aging. It found no significant differences in hematological values between young and old dogs of middle-sized breeds, excepting MCV (mean corpuscular volume) and MPV (mean platelet volume). Corpuscular volume was increased in young dogs, but platelet parameters were the most significantly different, with platelet volume markedly higher in young dogs than the accepted adult level. However, this study used dogs between 1-3 years old as their ‘young’ group, and dogs aged 7-10 as the ‘older’ group. Since canines usually reach maturation between 6-18 months of age, this study is not helpful in assessing data from puppies but is useful to recognize that these differences become statistically insignificant once the dogs are over a year old in mid to large-sized breeds.

An interesting deviation from the earlier mentioned studies is found in Rortveit et al., 2015, which found similarly low values in puppies for RBC, hematocrit, and hemoglobin concentration but no statistically different values for white blood cells including lymphocyte counts, neutrophil count, and eosinophil count. This is at odds with previous studies by Harper et al., Brenten et al., and Yi et al. but implies that care must be taken when interpreting hematological results.

References

Brenten, T., Morris, P.J., Salt, C., Raila, J., Kohn, B., Schweigert, F. & Zentek, J. (2016) ‘Age-associated and breed-associated variations in haematological and biochemical variables in young Labrador retriever and minature schnauzer dogs’ Vet Record Open 3 pp.1-9

Harper, E.J., Hackett, R.M., Wilkinson, J. & Heaton, P.R. (2003) ‘Age related variations in hematologic and plasma biochemical test results in Beagles and Labrador Retrievers’ JAVMA 222:10 pp 1436-1442

Lee, S.H., Kim, J.W., Lee, B.C. & Oh, H.J. (2020) ‘Age-specific variations in hematological and biochemical parameters in middle- and large-sized of dogs’ J Vet Sci. 21:1

Rortveit, R., Saevik, B.K., Eggertsdottir, A.V., Skancke, E., Lingaas, F., Thoresen, S. & Jansen, J.H. (2015) ‘Age-related changes in hematologic and serum biochemical variables in dogs aged 16-60 days’ Vet Clin Pathol 44:1 pp. 47-57

Yi, S., Kim, E., Oh, S., Ha, J., Lee, B., Yoo, J. & Do, Y. (2019) ‘Changes in the complete blood count and serum biochemical parameters of Sapsaree dogs according to different age groups’ Korean Journal of Veterinary Service 42:4 pp. 227-236