Feline Biochemistry: Variations with Age

Kitten physiology is different from that of an adult cat, so obtaining a kitten-specific biochemistry is important for a more accurate interpretation.
Kitten physiology is different from that of an adult cat, so obtaining a kitten-specific biochemistry is important for a more accurate interpretation.
March 3, 2023

By Dr Lizzie Youens BSc(Hons) BVSc MRCVS

Cats are the champions of hiding signs of illness and disease, and a history and clinical examination of a sick feline may often reveal only non-specific signs such as lethargy or mild pyrexia. Veterinarians interested in feline medicine are the detectives of the veterinary world, decoding subtle signs and hunting for clues. When presented with a sick cat, many veterinarians will often perform a minimum database to obtain some objective parameters with the intention that the results will guide clinical decision making.

A sick kitten in particular can be even more challenging to diagnose and treat. Neonatal animals who are not thriving often have reduced capacity of some organ systems, metabolism, and enzymatic processes, all of which will alter physiological parameters. Performing a biochemical assessment on kittens could help inform specific and appropriate care as long as an age-appropriate evaluation is implemented.

Read on to learn more about what biochemistry parameters are appropriate for each stage of kitten development along with the implications these values have on interpretation. 

Why might I need a kitten biochemistry?

Sick kittens can deteriorate rapidly, and veterinarians must act swiftly to gather measurable data alongside the history and clinical exam to gain an accurate understanding of the problem. Chemistry profiles give insight into the state and function of various organs and systems. A chemistry profile is often performed alongside a complete blood count (CBC) to gain a fuller understanding of the health and wellness of a pet. 

Obtaining a kitten chemistry sample

The sample requirement for a biochemistry profile is usually a small amount of venous blood, which is allowed to clot and is then separated for serum or plasma. 

Venipuncture is usually performed from the jugular vein, with the kitten in dorsal recumbency, head and neck extended. Care must be taken with restraint in sick kittens, who are prone to stress, and a peripheral vein may be used if easier. Approximately 0.25ml of serum is required. 

Interpreting feline chemistry: kittens vs adult cats

Kitten physiology is different from that of an adult cat, which will affect reference interval results. Biochemical parameters are often closely regulated, with very tight reference ranges, and so small variations due to developing physiology could be interpreted as being abnormal. 

All results should be assessed individually, with due consideration of age, breed, and sex differences. 

The evidence behind age-related changes in biochemistry parameters

A study of 91 healthy cats (Nakai et al., 1992) with an age range of one and 48 months old revealed how some biochemical parameters change as kittens age. Total protein and albumin values were both initially low in neonatal kittens and then stabilized to adult levels by around 9-11 months of age. On the other hand, alkaline phosphatase (ALP), phosphorus, bilirubin, cholesterol, glucose and triglycerides were all higher in young kittens before dropping to adult levels. Some parameters, such as triglycerides and phosphorus, didn’t reach adult levels until around 18 months of age, so interpreting these results should be done carefully even after what is traditionally defined as feline adulthood.  

Further study in 2006 (Levy et al., 2006) corroborated these results, although the stabilization to adult levels was found to be more rapid with most parameters stabilizing within the first 12 weeks. 

Additionally, investigation into mineral metabolism in cats (Pineda et al., 2013) found marked changes in calcium, phosphorus, and magnesium levels between kittens and adult cats.  

Reference intervals for kitten biochemistry

There are some important differences in reference intervals for various biochemical parameters in kittens as compared to adults. 

These figures are based on results from Levy et al. (2006) and Nakai et al. (1992). 

Parameter < 3 months 4-6 months 7-12 months
ALT (U/L) 10-50 < 77 < 85
ALP (U/L) <564 37-333 21-197
Creatinine (mg/dl) 0.16-1.26 0.33-1.21 0.8-2.3
Total protein (g/dl) 2.1-4.5 3.3-7.5 3.3-7.5
Albumin (g/dl) 2.4-3.0 2.6-3.1 2.8-3.9
Phosphorus (mg/dl) 6.5-10.1 6.0-10.4 4.5-8.5
Bilirubin (mg/dl) < 3 < 4 < 4
Cholesterol 119-213 124-221 65-195
Glucose (mg/dl) 80-170 70-150 70-140

How do these values affect interpretation?

Biochemical parameters are normally tightly regulated, and so small differences to reference intervals can cause alarm. Veterinarians should recognize that abnormal values may be due to growth and physiological changes rather than disease.

Here are some key points from the available data.

  • ALP is markedly elevated in young kittens. This is assumed to be due to bone growth.
  • Phosphorus and calcium levels are also elevated in the first few weeks of a kitten’s life, likely also due to rapid bone development.
  • Protein levels are initially low in kittens and only stabilize by around six months of age. This is likely caused by an immature and low-functioning immune system.
  • Globulin levels are initially high in very young kittens due to colostrum intake but then rapidly decrease.
  • Creatinine values are often low in young kittens due to low muscle mass.

The practicalities of these points can be invaluable when interpreting a kitten chemistry profile. 

  • An ALP of 500U/L in a kitten could lead to concerns about liver disease, such as a congenital fault or toxin ingestion, when in fact that is a normal value.
  • A calcium level of 13mg/dl would register as hypercalcemia, sparking an investigation into differential diagnoses such as renal disease or neoplasia, when in fact the elevated level is normal for the age
  • A total protein count of 3.1g/dl could be flagged as hypoproteinemia, leading to concern regarding an enteropathy or nephropathy, when in fact low protein levels are normal in neonatal cats. 

Considering age as an important factor when interpreting feline chemistry results is paramount to obtaining accurate and specific action. 


Levy, J.K., Crawford, P.C. & Werner, L.L. (2006) ‘Effect of age on reference intervals of serum biochemical values in kittens’ J Am Vet Med Assoc 229(7) pp.1033-1037

Nakai, N., Nawa, K., Maekawa, M. & Nagasawa, H. (1992) ‘Age-related changes in hematological and serum biochemical values in cats.’ Jikken Dobutsu 41:3 pp.287-94

Pineda, C., Aguilera-Tegero, E., Guerrero, F. & Raya, A.I. (2013) ‘Mineral metabolism in growing cats: changes in the values of blood parameters with age.’


Feline Biochemistry: Variations with Age

Kitten physiology is different from that of an adult cat, so obtaining a kitten-specific biochemistry is important. Learn what parameters are important to measure and how wellness levels within these categories change from three months onward.

March 3, 2023
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