Because chronic kidney disease (CKD) is common in cats and Birman cats have a physiologically high concentration of serum creatinine and urea compared with the general feline population (mechanism unknown), the investigators looked to methods to better evaluate CKD in this breed. Their aim was to assess whether in contrast to serum creatinine, the serum concentration of symmetric dimethylarginine (SDMA) is comparable in healthy Birmans and in the general cat population. The authors state that CKD risks may be overestimated as the result of this physiologically high concentration of serum creatinine in the breed. Detecting a high serum creatinine often may lead to clients and veterinarians performing unnecessary and stressful clinical and laboratory work-ups to rule out the presence of CKD.
SDMA is excreted by the kidneys and the correlation between glomerular filtration rate (GFR) and creatinine and GFR and SDMA are almost identical. The serum concentration of SDMA increases when GFR decreases which occurs during CKD. One study has shown the increase of SDMA above the reference interval (RI) occurs earlier than the increase of creatinine in cats with CKD. The authors decided to assess whether SDMA might be a good marker to monitor the health of this breed. Their aim was to see if clinically healthy Birman cats have normal SDMA concentrations when compared with a general feline laboratory reference interval and at the same time, define the breed specific RI for SDMA.
The authors included in the study 50 Birman cats of and age range of 6 months to 13 years (median 4 years). The other remaining 46 cats belonged to eight different breeds with an age range of 6 months to 17 years (median 9 years). All the Birman cats were clinically healthy and the cats of other breeds did not have clinical signs consistent with kidney disease.
The results indicated that serum creatinine (1.58 ± 0.36 mg/dl) and SDMA (12.2 ± 2.8 m/dl) were higher in Birmans than in cats of other breeds (1.19 ± 0.17 mg/dl; 10.3 ± 2.5 mg/dl). No significant sex-related differences were noted for SDMA among Birman cats or among cats of other breeds.
The results also indicated that in 20 of the 50 (40.0%) Birman cats, serum creatinine was higher than both the non-breed-specific RI of the author’s laboratory and the threshold recommended to classify cats as IRIS stage 2 (1.6 mg/dl). Considering SDMA concentrations, the values were higher than the pre-existing RI in 10/50 (20.0%) Birmans and in four cats of other breeds. Among the Birman group, it was found the proportion of cats with SDMA > 14 mg/dl was lower than the proportion of cats with creatinine > 1.6 mg/dl. The breed-specific RI developed in this study for Birman cats (3.4-19.2 g/dl) primarily overlapped the pre-existing one (0.0-14.0 g/dl).
The authors state the results confirm the hypothesis of the study that SDMA is less frequently and less severely increased than creatinine in Birman cats. Yet, they also agree that the results confirm the importance of using a breed-specific RI for investigating renal function in Birman cats. SDMA could be recommended as the marker of choice for routine investigation in this breed and should be included in any general health screening profile of these cats. Using both creatinine and SDMA for analysis would help prevent over-diagnosis of CKD or staging errors in Birman cats by investigating primarily those Birman cats that have creatinine concentrations outside of the breed-specific RIs or SDMA concentrations that are largely outside of the RI of the general cat population. (VT)