Which statement about SDMA as a biomarker is true?

• A. Elevated creatinine with normal SDMA
• B. SDMA remains normal until late CKD
• C. SDMA increases earlier than creatinine in kidney disease
• D. SDMA is a marker of liver function

Answer: (C)

SDMA rises as kidney function declines because it is cleared mainly by glomerular filtration and is produced at a steady rate, with little influence from muscle mass or diet. As GFR falls, SDMA accumulates in the blood, often becoming abnormal before creatinine does. Creatinine levels can be affected by muscle mass, age, and nutritional status, so it may stay within the normal range even as kidney function begins to deteriorate. This is why SDMA is considered an earlier and more sensitive indicator of renal dysfunction in dogs, especially in senior patients.

SDMA is not a marker of liver function. The idea that it would reflect liver status doesn’t fit its renal clearance pattern. The scenario where creatinine is elevated while SDMA remains normal is inconsistent with SDMA’s behavior as an early kidney function marker, and the notion that SDMA stays normal until late CKD contradicts its demonstrated early rise.