Is canine calprotectin in serum stabile after storage at low temperature?

BACKGROUND: In human and veterinary medicine calprotectin is most widely used in diagnosing different gastro-intestinal diseases. The aim of this study was to assess the stability of canine calprotectin (cCP) in serum after storage at low temperatures and imprecision of the method. METHODS: Blood samples were collected from dogs with different clinical diagnoses. Twenty-two dogs were included in this study. Calprotectin concentration was measured 4 hours after serum separation (T0), and after being frozen at − 80 °C for 8 (T1) and 16 weeks (T2). The maximum permissible difference (MPD) was derived from the equation for calculating total error (TE) TE = %Bias + (1.96 x %CV), where bias and coefficient of variation (CV) were defined by the manufacturer. The dogs enrolled in this study were patients admitted during the morning (9–12 a.m.), on the day the first measurement was performed. All sample analysis for determination of stability were done in duplicates. For determination of within-run precision, the two patients’ serum samples were analyzed in 20 replicates. Imprecision was assessed by analyzing 20 replicates on one plate on two samples where high and low concentrations were anticipated. RESULTS: The calculated value of MPD was 32.52%. Median calprotectin concentrations were higher at T1 114.08 μg/L (IQR = 55.05–254.56) and T2 133.6 μg/L (IQR = 100.57–332.98) than at T0 83.60 μg/L (IQR = 50.38–176.07). Relative and absolute bias at T1 (49.3%; 45.98 μg/L) and T2 (109.93%; 94.09 μg /L) have shown that calprotectin concentrations increase after long term storage at − 80 °C. CONCLUSION: The results of the present study indicate that c-CP was not stable for 16 weeks at low storage temperature (− 80 °C). Considering the observed change in the concentration of c-CP at T1, a storage time of 8 weeks should be safely applied. The method imprecision was not satisfactory, especially in the lower concentration range.