How to Diagnose Chronic Kidney Disease
Diagnose CKD by measuring both serum creatinine to calculate eGFR and urine albumin-to-creatinine ratio (ACR), with abnormalities persisting for at least 3 months—either eGFR <60 mL/min/1.73 m² OR albuminuria ≥30 mg/g confirms the diagnosis. 1
Diagnostic Criteria
CKD requires abnormalities of kidney structure or function present for >3 months with health consequences 1. The 3-month duration requirement distinguishes CKD from acute kidney injury 1. You must demonstrate either:
- Decreased kidney function: eGFR <60 mL/min/1.73 m² 1
- Evidence of kidney damage: Primarily albuminuria (ACR ≥30 mg/g) 1
Essential Initial Testing
Measure Both Parameters Simultaneously
Always order both tests together—eGFR and ACR provide independent prognostic information and CKD can be diagnosed by either abnormality alone 1:
- Serum creatinine to calculate eGFR using the 2021 CKD-EPI equation (race-free) 2, 1
- Urine albumin-to-creatinine ratio (ACR) on a random spot urine collection 1
Confirm Chronicity
Following detection of elevated ACR or low eGFR, repeat tests to confirm presence of CKD 1. Proof of chronicity can be established by 1:
- Review of past GFR or albuminuria measurements
- Imaging findings showing small kidneys or cortical thinning
- Medical history consistent with chronic disease
- Repeat measurements beyond the 3-month point
Common pitfall: Do not rely on serum creatinine alone—always calculate eGFR using validated equations 3. Do not skip albuminuria testing, as eGFR and ACR provide independent prognostic information for cardiovascular events, CKD progression, and mortality 3.
Who to Screen
Target these high-risk populations for CKD screening 3, 4:
- Diabetes mellitus (screen at diagnosis for type 2,5 years after diagnosis for type 1) 1
- Hypertension 4
- Age >60 years 3
- Family history of kidney disease 3
- Cardiovascular disease 5
- Obesity 5
All persons should be assessed during routine health encounters to determine if they are at increased risk for CKD based on clinical and sociodemographic factors 3.
Staging CKD
Once diagnosed, stage CKD using both GFR and albuminuria categories 1:
GFR Categories (G stages):
- G1: ≥90 mL/min/1.73 m² (with evidence of kidney damage)
- G2: 60-89 mL/min/1.73 m²
- G3a: 45-59 mL/min/1.73 m²
- G3b: 30-44 mL/min/1.73 m²
- G4: 15-29 mL/min/1.73 m²
- G5: <15 mL/min/1.73 m² 1
Albuminuria Categories (A stages):
- A1: <30 mg/g (normal to mildly increased)
- A2: 30-300 mg/g (moderately increased)
- A3: >300 mg/g (severely increased) 1
Additional Evaluation to Determine Cause
Comprehensive History Focusing On:
- Diabetes duration and control 1
- Hypertension duration and control 1
- Family history of kidney disease 1
- Medication history (NSAIDs, lithium, calcineurin inhibitors, aminoglycosides) 3, 1
- Systemic diseases associated with kidney involvement 1
Basic Laboratory Tests:
- Complete blood count 1
- Comprehensive metabolic panel (including electrolytes, bicarbonate for metabolic acidosis) 3, 1
- Urinalysis with microscopy (looking for hematuria, pyuria, or casts suggesting glomerulonephritis) 3, 1
- Urine protein quantification 1
Additional Tests Based on Clinical Suspicion:
- Serologic testing for autoimmune diseases 1
- Complement levels 1
- Hepatitis B/C and HIV serology 1
- Serum and urine protein electrophoresis 1
Role of Imaging
Renal Ultrasound
Measure serum creatinine, eGFR, and urine ACR in all patients with hypertension or suspected CKD 2. Renal ultrasound should be considered in hypertensive patients with CKD to assess kidney structure, determine causes of CKD, and exclude renoparenchymal and renovascular hypertension 2.
Ultrasound can differentiate acute kidney injury from CKD by determining renal size and volume 2:
- Small kidneys (<9 cm in adults) with cortical thinning suggest chronic disease 2
- Normal-sized kidneys do not exclude CKD—kidney size is initially preserved in diabetic nephropathy and infiltrative disorders 2, 3
- Increased renal echogenicity is a nonspecific manifestation of renal disease 2
Important caveat: In patients with CKD and diabetes or hypertension, ultrasound has minimal impact on diagnosis and management 2. Ultrasound may be indicated when there is prior history of stones, obstruction, renal artery stenosis, frequent urinary tract infections, or family history of autosomal dominant polycystic kidney disease 2.
Advanced Imaging
CT or magnetic resonance renal angiography are alternative testing options when renovascular disease is suspected 2.
When to Consider Kidney Biopsy
Consider kidney biopsy when 1:
- The cause is unclear and results would guide treatment decisions
- Rapidly progressive disease
- Nephrotic syndrome
- Suspected glomerular disease
- Up to 30% of patients with presumed diabetic kidney disease have other causes on biopsy 3
Monitoring Frequency After Diagnosis
If moderate-to-severe CKD is diagnosed (eGFR <60 mL/min/1.73 m² or albuminuria ≥30 mg/g), repeat measurements of serum creatinine, eGFR, and urine ACR at least annually 2. Monitoring frequency should be intensified based on risk stratification 3:
- Low risk (eGFR ≥60 with UACR <30 mg/g): Annual monitoring 3
- Moderate risk (eGFR 45-59 or UACR 30-300 mg/g): 2 times per year 3
- High risk (eGFR 30-44 or UACR >300 mg/g): 3 times per year 3
- Very high risk (eGFR <30 or UACR >300 mg/g with other risk factors): 4 times per year 3
When to Refer to Nephrology
Refer to nephrology when 1, 4:
- eGFR <30 mL/min/1.73 m² 1, 4
- Significant proteinuria (UACR ≥300 mg/g) 4
- Rapid decline in kidney function 1, 4
- Continuously increasing urinary albumin levels 3
- Continuously decreasing eGFR 3
- Difficulty in determining the cause of CKD 1
- Complex management issues or difficulty managing CKD complications 3, 1
- Uncertainty about etiology or atypical features suggesting non-diabetic kidney disease 3