Objective—To evaluate a human assay for quantification
of carboxy-terminal cross-linking telopeptide of
type I collagen (CTX-I), assess the influence of age on
plasma CTX-I concentration, investigate the relationship
between plasma CTX-I and serum osteocalcin
concentrations, and determine whether concentrations
of plasma CTX-I or serum osteocalcin fluctuate
in circadian manner in horses.
Horses—75 clinically normal horses.
Procedure—Cross-reactivity between equine serum
CTX-I and CTX-I antibodies in an automated electrochemiluminescent
sandwich antibody assay (ECLIA)
was evaluated via a specificity test (ie, dilution test) and
recovery calculation. Serum osteocalcin concentration
was measured with an equine-specific osteocalcin
radioimmunoassay. To analyze diurnal variations in plasma
CTX-I and serum osteocalcin concentrations, blood
samples were obtained hourly during a 24-hour period.
Results—Results of the dilution test indicated good
correlation ( r > 0.99) between expected serum CTX-I
concentrations and measured serum CTX-I concentrations.
The calculated CTX-I recovery was 97.6% to
109.9%. Plasma CTX-I and serum osteocalcin concentrations
were correlated. Plasma CTX-I concentration
was inversely correlated with age of the horse.
No significant circadian variations in plasma CTX-I and
serum osteocalcin concentrations were detected.
Conclusions and Clinical Relevance—Results suggest
that the fully automated CTX-I ECLIA can be
used for evaluation of plasma and serum samples
from horses and may be a useful tool to monitor bone
metabolism changes. Horses in this study did not
have notable diurnal fluctuations in serum osteocalcin
and plasma CTX-I concentrations. ( Am J Vet Res 2004;65:104–109)