Can albuminuria reflect early kidney injury even when filtration markers are preserved?

Albuminuria and estimated filtration rate capture different aspects of kidney health: albuminuria reflects abnormal albumin permeability/handling, whereas eGFR reflects overall filtration capacity. Thus, preserved eGFR does not rule out early kidney injury.

Clinical interpretation

• Persistent albuminuria is recognized as a marker of chronic kidney disease even when eGFR is ≥60 mL/min/1.73 m².
• The most strongly supported interpretation is early impairment of the glomerular filtration barrier. Albumin can appear in urine before a measurable reduction in filtration capacity.
• Albuminuria is not specific for a particular kidney lesion or disease process. A single urine albumin-to-creatinine ratio (ACR) ≥30 mg/g should be confirmed, preferably with a first-morning specimen and persistence for at least 3 months.

Mechanistic considerations

• The glomerular barrier comprises fenestrated endothelium and its glycocalyx, the glomerular basement membrane, and podocyte slit diaphragms. Dysfunction at any of these levels can reduce albumin selectivity and increase urinary albumin loss.
• Endothelial/glycocalyx injury offers a biologically credible link between albuminuria and renal microvascular dysfunction; experimental glycocalyx disruption increases albumin permeability.
• However, albuminuria with preserved eGFR does not directly establish measured renal microvascular injury in an individual. The microvascular interpretation remains plausible rather than definitively demonstrated by direct human structural evidence.

Broader risk implications

• Higher UACR is associated prospectively with cardiovascular events and heart failure across eGFR strata, including preserved kidney function. This supports albuminuria as a vascular and cardiovascular risk marker, though not proof of renal microvascular damage.

Bottom line

• Albuminuria with preserved filtration markers can reasonably signal early glomerular barrier injury and may reflect microvascular injury, but it requires repeat confirmation and clinical context because exercise, acute illness, and hematuria can transiently elevate ACR.