A preliminary investigation into the prognostic relevance of symmetric dimethylarginine in critically ill dogs

Validation of a reference interval for symmetric dimethylarginine in healthy goats and its comparison to values in goats with obstructive urolithiasis

BACKGROUND

Symmetric dimethylarginine (SDMA), a sensitive biomarker for detecting renal injury, has not been characterized in goats. Obstructive urolithiasis (OU) is the most common urinary tract disease in male small ruminants.

HYPOTHESIS/OBJECTIVE

Establish an SDMA reference interval (RI) in healthy adult goats and describe SDMA concentrations in goats with OU. We hypothesize that the SDMA RI in healthy adult goats will be similar to that of other adult veterinary species and that SDMA can be utilized to assess the renal function of goats experiencing OU.

ANIMALS

Fifty-five healthy adult male and female goats from a university herd were enrolled for SDMA RI development. Twenty male and female goats from a university herd were enrolled for validation of the SDMA RI established. Thirteen male goats diagnosed with OU were enrolled.

METHODS

Clinical trial. Serum samples for all animals enrolled were collected and analyzed for SDMA using an immunoassay (IDEXX Laboratories, Inc); goats with OU had additional blood work analyzed (PCV, total solids, and serum biochemistry). Symmetric dimethylarginine and other values in goats with OU were analyzed and compared at specific time points.

RESULTS

The SDMA RI for healthy, adult goats is 8.03 μg/dL (90% CI 4.81-11.04) to 25.93 μg/dL (90% CI 22.88-28.97). There was no correlation identified between serum creatinine and SDMA in goats with OU.

CONCLUSIONS AND CLINICAL IMPORTANCE

The SDMA RI for adult goats is higher than in other adult large animal species. Use of SDMA in goats with OU is not useful in assessing their renal function.

Evaluation of symmetric dimethylarginine in cats with acute kidney injury and chronic kidney disease

Background

Serum symmetric dimethylarginine (SDMA) concentrations are considered a biomarker for renal dysfunction in dogs and humans with acute kidney injury (AKI). No studies have assessed SDMA in cats with AKI.

Hypothesis/Objectives

SDMA correctly identifies cats with azotemic AKI.

Animals

Fifteen control cats, 22 with novel AKI, 13 with acute on chronic‐AKI (AoC) and 19 with chronic kidney disease (CKD).

Methods

Retrospective study. Cats with azotemia (serum creatinine concentrations >1.7 mg/dL) were defined as having AKI or CKD based on history, clinical signs, clinicopathological findings and diagnostic imaging, and classified using the International Renal Interest Society (IRIS) grading/staging systems. Serum SDMA concentrations were compared between groups with nonparametric methods, and correlations assessed using Spearman's correlation coefficient. Data are presented as median [range].

Results

SDMA concentrations were 11 (8‐21) μg/dL, 36 (9‐170)μg/dL, 33 (22‐75) μg/dL and 25 (12‐69) μg/dL in control, novel AKI, AoC and CKD cats. SDMA concentrations were significantly higher in cats with novel AKI (P < .001), AoC (P < .001) and CKD (P < .01) compared to controls. SDMA concentrations were significantly higher in cats with more advanced AKI (IRIS grade IV‐V) compared to less severe AKI (IRIS grade II). Serum creatinine and SDMA concentrations had a significant correlation in cats with novel AKI (r_s = 0.826, n = 22; P < .001) and a significant correlation when all cats across all 4 groups were considered together (r_s = 0.837, n = 69; P < .001).

Conclusions and Clinical Importance

Serum SDMA concentrations are elevated in cats with established AKI (novel and AoC) and CKD, providing evidence for use of SDMA as a biomarker for AKI in cats.

Symmetric dimethylarginine and renal function analysis in horses with dehydration

BACKGROUND

Acute dehydration caused by a variety of diseases in horses can lead to acute kidney injury. However, current renal biomarkers usually indicate renal damage late in the course of the disease. A novel biomarker would be helpful to diagnose renal disease earlier.

OBJECTIVES

(1) To estimate the correlation of serum symmetric dimethylarginine (SDMA) concentrations with the degree of dehydration, traditional renal biomarkers and renal function analysis, and (2) to determine the value of SDMA as a prognostic and early biomarker of renal injury in horses.

STUDY DESIGN

Prospective cohort.

METHODS

Serum SDMA, creatinine and urea concentrations and renal function analysis were measured in 41 horses with dehydration at 4 time points until 48 h after admission. Horses were grouped according to their dehydration level into mildly, moderately and severely dehydrated groups.

RESULTS

Serum SDMA concentrations at admission correlated with creatinine concentrations (r = .412, P < .001). Differences in SDMA concentrations at admission were detected among dehydration levels but not between survivors and nonsurvivors. Significant correlations of SDMA concentrations with other markers of renal function analysis and short-term outcome were not observed.

MAIN LIMITATIONS

Besides the small sample size and low statistical power, missing urine samples at specific time points were also 1 of the main limitations. Only 1 of the horses developed acute kidney injury, which made the evaluation of the predictive value of SDMA difficult.

CONCLUSIONS

SDMA concentrations correlated significantly with creatinine concentrations in dehydrated horses. Further research is needed to reveal the application of SDMA in horse.

Symmetric dimethylarginine and creatinine concentrations in serum of healthy draft horses

Background

Symmetric dimethylarginine (SDMA) is considered a more sensitive indirect estimate of glomerular filtration rate (GFR) than creatinine (Cr). Symmetric dimethylarginine is not affected by sex or muscle mass in small animals.

Objectives

To validate a commercial SDMA immunoassay (IA) for equine serum; to compare SDMA and Cr in cohorts of draft horse breeds; and to assess effects of age, sex, and breed.

Animals

One hundred and sixty‐five healthy draft horses (0.5‐16 years), including 63 Percherons, 52 Clydesdales, and 50 Belgians.

Methods

Cross‐sectional study. The SDMA IA was validated for equine serum by comparison to liquid chromatography‐mass spectroscopy (LC‐MS) results and other methods. Symmetric dimethylarginine and Cr were compared by analysis of variance and correlation analysis.

Results

Median and 95% confidence intervals (CIs) for LC‐MS (10.0 [9.4, 10.2] μg/dL) and IA (9.7 [9.5, 10.0] μg/dL) SDMA concentrations were strongly correlated (R = .74, P < .001). Symmetric dimethylarginine was lower (P < .01) in Percherons and Belgians, than in Clydesdales. Median values and 95% CI for Cr were 1.3 (1.2, 1.4), 1.4 (1.3, 1.5), and 1.4 (1.3, 1.5) mg/dL (P = .06) for Percherons, Clydesdales, and Belgians, respectively. Symmetric dimethylarginine was correlated to Cr (LC‐MS, R = .60, P < .001; IA, R = .66, P < .001). There were no differences in SDMA or Cr between sexes and there were no correlations between age and SDMA or Cr.

Conclusions and Clinical Importance

Although a significant breed effect on SDMA concentration was found, differences were small and all medians were <14 μg/dL, the cutoff value to support renal dysfunction in dogs and cats.

The new age of renal biomarkers: does SDMA solve all of our problems?

Within clinical small animal practice, diagnosis of both chronic kidney disease and acute kidney injury is common. To assess renal function, measurement of glomerular filtration rate is considered the gold standard. Currently, routine tests of kidney function include surrogate markers of glomerular filtration rate such as serum creatinine, and urea, each with their own limitations, whilst urine protein to creatinine ratio gives an indication of glomerular and tubular handling of protein, and urine specific gravity information about urine concentrating ability by the kidney. These parameters are used together with historical and physical examination data to give a diagnosis of kidney disease following which creatinine, proteinuria and blood pressure are used to stage chronic kidney disease and, together with urine output, grade acute kidney injury according to the International Renal Interest Society. However, there has been much concern that creatinine is insensitive when used to indicate early decline in renal function and this has highlighted the need for additional methods of diagnosing and monitoring these patients, with the potential to allow earlier therapeutic intervention. Symmetric dimethylarginine is a novel biomarker, which has been shown to perform as a surrogate marker of glomerular filtration rate in small animals. This article will review current research on symmetric dimethylarginine and the ways in which it may be utilised in small animal practice; current research supports the use of symmetric dimethylarginine as a screening test for detection of early chronic kidney disease according to International Renal Interest Society guidelines, but further research is required in to the usefulness of symmetric dimethylarginine as a tool for monitoring disease and the effect of non-renal influences.