Evaluation of Serum Symmetric Dimethylarginine Concentration as a Marker for Masked Chronic Kidney Disease in Cats With Hyperthyroidism

Abstract

BackgroundHyperthyroidism can complicate (mask) the diagnosis of chronic kidney disease (CKD) because it increases glomerular filtration rate and decreases body muscle mass, both of which can lower serum creatinine concentrations. Currently, there is no clinical test that can reliably predict which hyperthyroid cats have concurrent azotemic CKD that will become apparent after treatment of the hyperthyroidism.ObjectivesTo investigate serum symmetric dimethylarginine (SDMA) concentration as a potential marker of masked azotemia in untreated hyperthyroid cats.AnimalsTwo hundred and sixty‐two hyperthyroid cats and 206 aged‐matched, clinically normal cats.MethodsProspective study. We measured creatinine, urea nitrogen, SDMA, T4, and TSH concentrations before and 1, 3, and 6 months after treatment with radioiodine (131I) and classified 131I‐treated cats as azotemic or nonazotemic based on persistent, post‐treatment creatinine concentrations >2.1 mg/dL. Groups were compared via nonparametric tests, and diagnostic accuracy was determined by receiver operating characteristic analysis and logistic regression.ResultsNo hyperthyroid cats were azotemic before treatment, but 42 (16%) became azotemic when rechecked at 4–8 months (median, 6 months) after 131I treatment; of these, 14 had high SDMA concentrations before treatment. As a diagnostic test for pre‐azotemic (masked) CKD in untreated hyperthyroid cats, SDMA showed a sensitivity of 33.3% and specificity of 97.7%.Conclusions and Clinical ImportanceFinding a high serum SDMA concentration in a hyperthyroid cat can help predict development of azotemia after treatment. The test has high diagnostic test specificity (few false‐positive results) but relatively low sensitivity (fails to predict azotemia in most hyperthyroid cats).

Cardiovascular‐renal axis disorder and acute‐phase proteins in cats with congestive heart failure caused by primary cardiomyopathy

“…Both baseline and longitudinal study results in CHF cats supported SDMA being more sensitive than creatinine, a finding that is consistent with previous publications 18,19,56 . Compared with creatinine, even with less specificity for CKD, 18 SDMA has 2 advantages: (1) it is a more accurate renal function marker in cachexic cardiac patients with low lean body mass and (2) its superior sensitivity would allow earlier detection of changes in kidney function in acute heart failure, when secondary acute renal injury may still be reversible if prompt action is taken 54 .…”

“…Conventionally, serum creatinine concentration is used for monitoring renal function in patients with cardiac disease as a marker of glomerular filtration rate (GFR), but its sensitivity and specificity are inferior to the newer marker of GFR, symmetric dimethylarginine (SDMA) 13‐16 . Unlike creatinine, SDMA is not affected by body lean mass, 17 and it can detect renal dysfunction earlier than does serum creatinine concentration 18,19 . Apart from a recent study comparing SDMA in cats with hypertrophic cardiomyopathy (HCM) and primary renal disease, 2 the biomarker role of SDMA in cats with heart disease has not been reported.…”

Hyperthyroidism is not a risk factor for subclinical bacteriuria in cats: A prospective cohort study

“…All hyperthyroid cats referred to our clinic for treatment with radioiodine over the 22‐month period from January 2018 to October 2019 were evaluated for inclusion in this prospective cohort study. To be eligible for inclusion, hyperthyroid cats underwent a thorough evaluation that included review of past medical history, complete physical examination (including body weight, body, and muscle condition scoring), 14 routine laboratory testing (CBC, serum biochemical profile, and complete urinalysis), urine culture, determination of serum thyroid hormone concentrations (total T 4 and TSH), 15,16 and qualitative and quantitative thyroid scintigraphy 17 . In cats previously treated with methimazole, the drug was discontinued ≥7 days before evaluation.…”

Spontaneous primary hypothyroidism in 7 adult cats

“…Serum creatinine concentrations in the 4 azotemic cats ranged from 2.2 to 3.4 mg/dL; concomitant urine specific gravities were less‐than‐maximally concentrated <1.035 in 2 cats (1.015 and 1.034), and well concentrated in 2 (1.047 and 1.050). Only 1 of the 4 azotemic cats had a slightly high serum SDMA concentration (15 µg/dL); the other 3 had SDMA values (11, 12, and 13 µg/dL) that were in the upper tertile of the reference interval (≤14 µg/dL). In the 3 nonazotemic cats, serum creatinine concentrations were in upper half of the reference interval (1.5, 1.7, and 1.9 mg/dL).…”

“…This prospective case series included 7 adult cats with spontaneous hypothyroidism referred to the Animal Endocrine Clinic for evaluation over a 3.5‐year period from March 2014 to September 2017 and then followed until April 2018. Data collected for each cat included the following: age, breed, sex, reason for initial workup by referring veterinarian, clinical signs as reported by owners, dietary history, drugs and supplements administered, known concurrent illnesses, physical examination findings (including the presence or absence of thyroid goiter), routine laboratory findings (eg, complete blood count, serum biochemistry profile, symmetric dimethylarginine [SDMA] concentration, and urinalysis), complete serum thyroid panel (T 4 , fT 4 , and TSH concentrations), survey radiographs of the spine and limbs, and results of thyroid imaging studies (eg, thyroid scintigraphy, or ultrasound).…”