Markers of Structural Damage of the Kidney
The most common markers of kidney structural damage include albuminuria/proteinuria, abnormalities in urine sediment, abnormalities in kidney imaging results, and pathological abnormalities on kidney biopsy. 1
Primary Markers of Kidney Damage
Urine Markers
Albuminuria/Proteinuria
Urine Sediment Abnormalities
- Hematuria (presence of red blood cells)
- Leukocyturia (presence of white blood cells)
- Cellular casts (epithelial, granular, waxy)
- Crystals 2
Imaging Abnormalities
- Structural changes detected on ultrasound:
- Cysts 1
- Changes in kidney size or echogenicity
- Hydronephrosis
- Stones
- Masses
Pathological Findings
- Abnormalities on kidney biopsy:
- Glomerular changes
- Tubular changes
- Interstitial changes
- Vascular changes 1
Novel Biomarkers of Kidney Damage
Several emerging biomarkers show promise for detecting kidney damage earlier than traditional markers:
Tubular Damage Markers:
Glomerular Damage Markers:
Clinical Application of Kidney Damage Markers
CKD Definition and Staging
Chronic Kidney Disease (CKD) is defined as either:
- Kidney damage persisting for ≥3 months, with or without decreased GFR, OR
- GFR <60 mL/min/1.73 m² persisting for ≥3 months, with or without evidence of kidney damage 2
CKD Stages Based on GFR and Markers of Damage
| Stage | GFR (mL/min/1.73 m²) | Description | With Kidney Damage | Without Kidney Damage |
|---|---|---|---|---|
| 1 | ≥90 | Normal or elevated GFR | CKD | Not CKD |
| 2 | 60-89 | Mildly decreased GFR | CKD | Not CKD |
| 3 | 30-59 | Moderately decreased GFR | CKD | CKD |
| 4 | 15-29 | Severely decreased GFR | CKD | CKD |
| 5 | <15 or dialysis | Kidney failure | CKD | CKD |
Albuminuria Categories
| Category | UACR (mg/g) | Description |
|---|---|---|
| A1 | <30 | Normal to mildly increased |
| A2 | 30-300 | Moderately increased |
| A3 | >300 | Severely increased |
Monitoring Recommendations
Frequency of monitoring should be based on GFR level and albuminuria:
- GFR ≥60 (with normal UACR): Annually
- GFR 45-59: Every 6-12 months
- GFR 30-44: Every 3-6 months
- GFR 15-29: Every 3 months
- GFR <15: Monthly 2
Laboratory assessment should include:
- Serum creatinine with eGFR calculation using CKD-EPI equation
- Urine albumin-to-creatinine ratio (UACR)
- Complete electrolyte panel
- Blood urea nitrogen (BUN)
- Complete blood count (CBC) to assess for anemia 2
Important Clinical Considerations
- Albuminuria/proteinuria can precede GFR decline and has strong associations with disease progression 5, 6
- At any GFR level, the degree of albuminuria is associated with risk of cardiovascular disease, CKD progression, and mortality 2
- Markers of kidney damage should be confirmed over at least 3 months to establish chronicity 2
- Non-albumin proteinuria may indicate tubular rather than glomerular damage and should not be overlooked 2
- Novel biomarkers (KIM-1, NGAL) may detect kidney damage prior to changes in traditional markers 5, 3
Pitfalls to Avoid
- Relying solely on serum creatinine without calculating eGFR can lead to overestimation of kidney function 1
- Failing to repeat abnormal tests over 3 months can lead to delayed diagnosis of CKD 2
- Overlooking non-albumin proteinuria which may indicate tubular rather than glomerular damage 2
- Not considering age-related GFR decline when interpreting results in elderly patients 2
- Missing early kidney damage by not using appropriate biomarkers in high-risk populations 6
By systematically evaluating these markers of kidney structural damage, clinicians can identify kidney disease earlier, implement appropriate interventions, and potentially slow disease progression.