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Azotemia: elevated BUN, creatinine and SDMA, read with urine specific gravity

Azotemia in a dog or cat means urea nitrogen, creatinine or both sit above the lab's interval, and the urine specific gravity from the same visit is what points the cause before, within or after the kidney.

Reviewed by Brian Toncray, DVM · October 22, 2026

Azotemia is a laboratory finding, not a diagnosis. The ISFM consensus guidelines on feline chronic kidney disease build the diagnosis on azotemia together with inadequately concentrated urine, documented over time, with hydration and imaging taken into account¹. The same three-way frame applies to dogs: reduced delivery of blood to the kidney, reduced function of the kidney itself, or urine that cannot leave the body. Acute kidney injury carries its own long list of causes and can arrive on top of chronic disease².

BUN (blood urea nitrogen)

High can mean: Prerenal: dehydration or reduced renal perfusion. Renal: reduced glomerular filtration from acute or chronic kidney disease^1,2. Postrenal: urethral obstruction, which disturbs fluid balance, electrolytes and acid-base status and causes retention of metabolic wastes³, or a ruptured urinary tract with urine in the abdomen⁴. Dogs with hypoadrenocorticism are often azotemic with poorly concentrated urine, which makes them look like primary kidney failure⁵.
Low can mean: Reduced hepatic synthesis. In advanced canine liver disease, low urea sits beside low albumin, glucose or cholesterol as a marker of failing function⁶.
Can shift it artificially: Hydration at the moment of sampling. A dehydrated patient can be azotemic for reasons that resolve with fluids, which is why the guidelines stage kidney disease only in a stable, hydrated patient¹.
Next test: Urine specific gravity on a sample from the same visit; full urinalysis; bladder palpation and imaging when obstruction or leakage is possible; a repeat panel after rehydration.

Creatinine

High can mean: The same prerenal, renal and postrenal list as BUN, with creatinine tracking glomerular filtration more closely because diet and liver function affect it less¹. In acute kidney injury, the rise can be rapid and the causes range from toxins to infection to ischemia².
Low can mean: Low muscle mass. Creatinine is produced by muscle, so a thin, older cat can carry a creatinine inside the interval while its filtration is already reduced¹.
Can shift it artificially: Muscle mass, as above. This is the main reason SDMA is measured alongside it.
Next test: Urine specific gravity, urine protein to creatinine ratio, blood pressure and imaging, which are the steps the feline guidelines set out for staging and management¹.

SDMA (symmetric dimethylarginine)

High can mean: Reduced glomerular filtration. In a retrospective feline study, SDMA rose before creatinine in 17 of 21 cats with chronic kidney disease, by a mean of 17 months⁷. In dogs with necropsy-confirmed chronic kidney disease, SDMA rose before creatinine in 17 of 19, by a mean of 9.8 months⁸. SDMA is also raised in cats with established acute kidney injury and in acute-on-chronic disease, so a high result does not by itself say which⁹.
Low can mean: No clinical meaning in the cited studies.
Can shift it artificially: In the feline study, SDMA had lower specificity than creatinine, so a lone, mild rise in an otherwise unremarkable cat is repeated before it is called kidney disease⁷.
Next test: Repeat SDMA and creatinine, check urine specific gravity and protein, and read the history for an acute insult⁹.

Phosphorus

High can mean: Reduced filtration in kidney disease, where phosphate is monitored as part of staging and management in cats¹. In a series of hypercalcemic cats, phosphorus was higher in those with renal failure than in those with neoplasia¹⁰.
Low can mean: Not a focus of this page; low phosphorus belongs with the calcium page when calcium is high.
Can shift it artificially: Read phosphorus with calcium and creatinine from the same sample rather than alone.
Next test: Calcium, ideally ionized, when both move; serial monitoring in confirmed kidney disease¹.

Urine specific gravity (USG)

High can mean: Concentrated urine beside azotemia supports a prerenal cause, because kidneys that can concentrate are still working¹.
Low can mean: Inadequately concentrated urine beside azotemia supports a renal cause¹, but extrarenal problems that blunt concentrating ability can mimic it. Hypoadrenocorticism is the classic trap in dogs⁵. In hypercalcemic cats with uroliths, azotemia was common, yet their urea nitrogen, creatinine and USG differed from those of cats with renal failure¹⁰.
Can shift it artificially: Use urine collected at the same visit as the blood, so the two describe the same moment in the patient's hydration.
Next test: Full urinalysis with sediment, and culture when the sediment or history calls for it.

Reading these values together

Start with USG. Azotemia with well-concentrated urine leans prerenal; azotemia with poorly concentrated urine leans renal, after hypoadrenocorticism and other extrarenal causes have been considered^1,5. Postrenal azotemia is a physical-exam diagnosis first: a large, firm bladder in a straining male cat, or abdominal fluid after trauma^3,4. When azotemia, hyperkalemia and abdominal effusion appear together, compare the creatinine in the abdominal fluid with the serum creatinine; a fluid value markedly higher than serum supports uroabdomen⁴.

Acute or chronic is the next question. SDMA rises in both, so it does not settle it⁹. History, kidney size and shape on imaging, and the trend across repeat panels do. The feline guidelines stage chronic disease only once the patient is stable and hydrated, using creatinine and SDMA, then substage by proteinuria and blood pressure¹.

Example: a panel worked through

Example. A 14-year-old neutered male domestic shorthair has lost weight over several months and drinks more. BUN, creatinine and SDMA are above the lab's interval, phosphorus sits at the top of the interval, USG is poorly concentrated and the PCV is mildly below the interval.

With a concentrating defect beside the azotemia, this reads as renal azotemia¹. The cat is mildly dehydrated, so the panel is repeated after rehydration before any stage is assigned. Urine protein to creatinine ratio, blood pressure and kidney imaging follow, and total T4 is checked because hyperthyroidism is common in cats of this age¹¹. The mild anemia is consistent with chronic kidney disease in cats but still gets a reticulocyte count¹.

Frequently asked questions

What does elevated BUN and creatinine mean in a cat?

Azotemia. Read it with urine specific gravity from the same visit: concentrated urine leans prerenal, poorly concentrated urine leans renal, and a blocked or ruptured urinary tract is postrenal^1,3.

Is azotemia always kidney disease?

No. Dehydration, hypoadrenocorticism, urethral obstruction and uroabdomen all cause azotemia, and the first two can come with poorly concentrated urine^5,4.

Why is SDMA high when creatinine is normal?

SDMA rises earlier than creatinine as filtration falls, and creatinine is held down by low muscle mass, so SDMA can flag reduced filtration first. A lone mild rise is repeated before it is labeled^7,8.

Can SDMA tell acute kidney injury from chronic kidney disease?

No. It is raised in both, so history, imaging and serial results decide⁹.

Sources

Sparkes AH, Caney S, Chalhoub S, et al. ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. J Feline Med Surg. 2016; 18(3):219-39. PMID: 26936494. DOI: 10.1177/1098612X16631234.
Ross L. Acute Kidney Injury in Dogs and Cats. Vet Clin North Am Small Anim Pract. 2022; 52(3):659-672. PMID: 35379499. DOI: 10.1016/j.cvsm.2022.01.005.
Bartges JW, Finco DR, Polzin DJ, et al. Pathophysiology of urethral obstruction. Vet Clin North Am Small Anim Pract. 1996; 26(2):255-64. PMID: 8711861.
Stafford JR, Bartges JW. A clinical review of pathophysiology, diagnosis, and treatment of uroabdomen in the dog and cat. J Vet Emerg Crit Care (San Antonio). 2013; 23(2):216-29. PMID: 23470168. DOI: 10.1111/vec.12033.
Klein SC, Peterson ME. Canine hypoadrenocorticism: part I. Can Vet J. 2010; 51(1):63-9. PMID: 20357943.
Webster CRL, Center SA, Cullen JM, et al. ACVIM consensus statement on the diagnosis and treatment of chronic hepatitis in dogs. J Vet Intern Med. 2019; 33(3):1173-1200. PMID: 30844094. DOI: 10.1111/jvim.15467.
Hall JA, Yerramilli M, Obare E, et al. Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in cats with chronic kidney disease. J Vet Intern Med. 2014; 28(6):1676-83. PMID: 25231385. DOI: 10.1111/jvim.12445.
Hall JA, Yerramilli M, Obare E, et al. Serum Concentrations of Symmetric Dimethylarginine and Creatinine in Dogs with Naturally Occurring Chronic Kidney Disease. J Vet Intern Med. 2016; 30(3):794-802. PMID: 27103204. DOI: 10.1111/jvim.13942.
Loane SC, Thomson JM, Williams TL, et al. Evaluation of symmetric dimethylarginine in cats with acute kidney injury and chronic kidney disease. J Vet Intern Med. 2022; 36(5):1669-1676. PMID: 35903963. DOI: 10.1111/jvim.16497.
Savary KC, Price GS, Vaden SL. Hypercalcemia in cats: a retrospective study of 71 cases (1991-1997). J Vet Intern Med. 2000; 14(2):184-9. PMID: 10772491. DOI: 10.1892/0891-6640(2000)014<0184:hicars>2.3.co;2.
Berent AC, Drobatz KJ, Ziemer L, et al. Liver function in cats with hyperthyroidism before and after 131I therapy. J Vet Intern Med. 2007; 21(6):1217-23. PMID: 18196729. DOI: 10.1892/07-022.1.