Do an undetectable UACR and optimal SDMA provide reassuring kidney context without measuring TMAO clearance?

A 52-year-old man with an undetectable UACR and laboratory-appropriate non-elevated SDMA has favorable—but targeted—renal context. These measures address albuminuria and indirectly filtration, not TMAO-specific elimination.

Kidney context

• Undetectable UACR is strongly reassuring for absence of clinically significant albuminuria and falls within KDIGO A1 (<30 mg/g). It supports intact glomerular permeability on the tested sample.
• This does not establish globally normal kidney function: CKD can occur with UACR <30 mg/g when eGFR is persistently <60 mL/min/1.73 m² or other kidney-damage markers are present. Non-albuminuric vascular, ischemic, tubulointerstitial, or fibrotic disease may also reduce filtration without albumin leakage.
• SDMA is a plausible adjunctive filtration signal. It is predominantly renally cleared and correlated strongly with measured GFR in one adult comparison (r = −0.84). However, “optimal” is assay-specific (reported reference ranges include ~0.32–0.65 µmol/L), and SDMA is not a KDIGO-recommended standalone marker for CKD diagnosis or staging.

TMAO clearance and mechanism

• Neither UACR nor SDMA directly quantifies TMAO elimination. SDMA’s correlation with TMAO is only moderate (approximately r = 0.42), insufficient to serve as a clearance surrogate.
• Direct TMAO clearance requires paired plasma and timed urinary TMAO concentrations plus urine volume, typically quantified by LC-MS/MS. In human studies, TMAO clearance approximated measured GFR and mean fractional excretion was ~105%, supporting predominant filtration; yet loop diuretics and red-meat intake can reduce fractional excretion, indicating modifiable tubular handling.

Bottom line

• Undetectable UACR and non-elevated SDMA are reassuring complementary kidney signals, but they cannot confirm normal TMAO clearance; eGFR/trajectory remain central for kidney context, while timed plasma–urine testing is needed for TMAO-specific clearance.