A comparison of two techniques for the determination of serum bone-specific alkaline phosphatase activity in dogs

Bone-specific alkaline phosphatase (BALP) shows potential as a marker of bo ne formation in the dog. Recent studies have indicated that serum BALP may provide a useful, non-invasive indicator of skeletal health in dogs, and as a diagnostic and prognostic marker in the management of dogs with musculos keletal or metabolic disorders. Two assay techniques tone based on wheatger m lectin precipitation followed by a simple enzymatic reaction, the second on a specific enzyme linked immunoassay) were used to measure serum levels of BALP in 35 dogs of different ages. As expected, BALP concentrations decreased with age. For the enzymatic assa y, mean (+/-SD) serum concentrations of BALP activities were 100.3 (+/-116) U/liter in dogs under 1 year of age, 25.3 (+/-6.8) U/L in dogs 1 to 2 year s of age, 16.5 (+/-7.3) Un in dogs 2 to 3 years of age, 14.3 (+/-5.6) Un in dogs 3 to 7 years of age, and 12.3 (+/-4.8) U/L in dogs aged 8 years and o lder. Corresponding results from the immunoassay were 56.3 (+/-9.8) U/L, 10 .7 (+/-4.5) U/L, 7.0 (+/-25) U/L, 6.7 (+/-3.6) U/L and 7.0 (+/-2.9) U/L. Th ere was excellent correlation between the results from the two assay techni ques (r = 0.96; P <0.0001). The correlation between BALP and total ALP acti vities was poor (r = 0.20 for enzymatic BALP, r = 0.31 for immunoreactive B ALP), indicating that total ALP should be considered unreliable as an indic ator of BALP activity in canine serum. The immunoassay demonstrated accepta ble (13 per cent) cross-reactivity with the liver isoform of ALP. The commercial immunoassay kit is simple and provides fast results. Althoug h the wheatgerm lectin/enzymatic technique is preferred in situations where the activities of all three isoforms of ALP are required, the immunoassay should be considered whenever the activity of BALP is the focus of interest .