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Canine CBC: Variations with Age

Age-specific interpretation is important in canine complete blood counts, such as in this Shiba Inu who is emerging into an adult dog.
Age-specific interpretation is important in canine complete blood counts, such as in this Shiba Inu who is emerging into an adult dog.
October 10, 2022

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? Get a CBC. Sick pup rushed in? Better get a puppy CBC! Geriatric dog slowing up? Probably needs a CBC! You get the picture. 

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.

 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 and cell morphology.

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 is sent to an external laboratory 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.

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 that of an adult.

This calls into question whether these standardized results are appropriate for diagnostic conclusions about 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 providing some potential values.

The below figures are from Harper et al. (2003) and correlate with a review by Brenten et al. (2016). Other puppy hematological values can be considered similar to adult reference intervals.

Reference intervals: neonate to adult

WBC (109/L)

Age Range Median
3.1-8 weeks 6.9-36.8 19
8 - 16 weeks 9.1-25.4 14.5
16 weeks – 1 year 8.6-32 18.5
>1 year 6.6-17.8 9.9

RBC (1012/L)

Age Range Median
3.1-8 weeks 4.1-5.9 4.9
8 - 16 weeks 3.8-6.6 5.1
16 weeks – 1 year 3.7-7.7 5.8
>1 year 5.8-8.3 7.1

Hemoglobin (g/L)

Age Range Median
3.1-8 weeks 82-142 123
8 - 16 weeks 86-149 126
16 weeks – 1 year 119-186 145
>1 year 142-191 165

HCT (L/L)

Age Range Median
3.1-8 weeks 0.29-0.41 0.36
8 - 16 weeks 0.28-0.46 0.38
16 weeks – 1 year 0.37-0.54 0.42
>1 year 0.42-0.56 0.48

Reference intervals: a summary

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

·  WBC count potentially varies with age. It is much higher 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 infection or other disease processes.

·  It is normal to see low values for Hb, RBC and HCT in young pups. This may not indicate anemia. Dogs will only reach 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.

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

A 2003 study (Harper et al., 2003) sampled 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 hematological variations 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, hemaglobin are all reduced in the first year of life. 

In contrast, a 2020 study (Lee et al., 2020) found no significant differences in hematological values between young and old dogs of middle-sized breeds, excepting MCV and MPV. 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 recognise 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. This is at odds with 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

Education
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Canine CBC: Variations with Age

The dog complete blood count (dog CBC) is a widely used tool in animal diagnostics around the world, but making sure to interpret reference intervals based on age is important for more accurate wellness statuses.

October 10, 2022
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