Clinical enzymology studies the enzyme activity in serum or other body fluids for the diagnosis, prognosis or monitoring of a variety of diseases. Clinical enzymology has greatly benefited from advances in technology and is now an integral part of laboratory analysis. However, to maximise the clinical benefits of serum enzyme measurement, clinicians and clinical pathologists must have a good understanding of the pathophysiology behind serum enzyme alterations. They must also be aware of the preanalytical and analytical factors that can affect the accuracy of serum enzyme activity measurement. This review article first covers the basic concepts of clinical enzymology and the general mechanisms related to serum enzyme alterations. Then, the review discusses the potential effects of various preanalytical and analytical factors on enzyme activity measurement. Lastly, it explores the pathophysiology and clinical use of various serum enzymes in canine and feline medicine. The present review article aims to be a comprehensive one‐stop source for clinical pathologists and small animal practitioners.

Haemoglobin A1c (HbA1c), the major fraction of glycated haemoglobin, is widely used for the diagnosis and monitoring of diabetes mellitus in human beings. However, there is a paucity of literature on the most reliable methods available for measurement of canine HbA1c. The aim of this study was to validate a new automated capillary electrophoresis assay for canine HbA1c, to generate a reference interval and to assess the overlap performance of the assay for the diagnosis of diabetes mellitus. Eighty-three blood samples treated with EDTA were included in the study, comprising 63 from healthy dogs and 20 from diabetic dogs. Linearity was assessed by mixing canine samples of known HbA1c percentage in different proportions, precision was assessed by repeated (n = 8) measurement of five canine samples, and stability was assessed by measuring canine samples stored at 4 °C for 96 h and −20 °C for 4 weeks. The robust method was used to determine the reference interval. The assay was demonstrated to be linear (R² = 0.943). Intra-assay and inter-assay coefficients of variation (CVs) were 4.8% and 7.0%, respectively. CVs for blood samples stored at 4 °C and −20 °C were 7.2% and 11.2%, respectively. The reference interval was 0.6-2.7%. Dogs with diabetes mellitus had significantly (P < 0.001) higher mean HbA1c (5.24 ± 0.88%) compared to the reference population (1.64 ± 0.55%), with no overlap between results. A HbA1c cut-off of 3.3% clearly differentiated diabetic from healthy dogs. The capillary electrophoresis assay was properly validated for canine HbA1c and the reference interval was determined, while the overlap performance of the assay was excellent.