Blood Tests for Chronic Kidney Disease: What to Track
Chronic kidney disease affects 37 million Americans, most without knowing it. These blood tests track kidney function over time and help predict whether disease is progressing or stable — before it reaches the dialysis threshold.
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Get My Score →The Core Kidney Function Blood Tests
| Test | Normal / Target | What It Measures |
|---|---|---|
| eGFR (estimated GFR) | Above 60 mL/min/1.73m² | Estimated filtering capacity — main CKD staging tool |
| Creatinine (serum) | 0.6–1.2 mg/dL (women); 0.7–1.3 mg/dL (men) | Waste product from muscle; rises as filtration falls |
| BUN (blood urea nitrogen) | 7–25 mg/dL | Nitrogen waste from protein — rises with kidney impairment |
| BUN:creatinine ratio | 10:1 to 20:1 | Ratio above 20 suggests dehydration or high protein intake, not kidney disease alone |
| Urine albumin:creatinine ratio (uACR) | Below 30 mg/g | Protein leaking into urine — earliest marker of kidney damage |
| Potassium | 3.5–5.0 mEq/L | Kidneys regulate potassium; rises in CKD, causing arrhythmia risk |
| Phosphate | 2.5–4.5 mg/dL | Rises in CKD; excess phosphate drives bone disease and calcification |
| Haemoglobin/CBC | Normal range | CKD anaemia — kidneys produce erythropoietin; falls as function declines |
CKD Staging by eGFR (KDIGO Guidelines)
CKD Staging: Why eGFR Matters
Chronic kidney disease is classified into 5 stages based on eGFR. Stage 1 (eGFR above 90) means kidney damage with normal filtration — uACR is positive but eGFR is preserved. Stage 2 (60–89) is mildly reduced function. Stage 3 (30–59) is moderately reduced — most metabolic complications begin here. Stage 4 (15–29) is severely reduced — preparation for renal replacement therapy begins. Stage 5 (below 15) is kidney failure. The transition from stage 3 to 4 is particularly important to identify, as interventions at this point can significantly slow progression.
uACR: The Earliest Warning
The urine albumin:creatinine ratio detects protein leaking into urine — the earliest sign of kidney damage. This occurs before eGFR falls. Microalbuminuria (uACR 30–300 mg/g) in a diabetic or hypertensive patient indicates the kidneys are already being damaged. Annual uACR testing in everyone with diabetes or hypertension is standard of care in the US. A uACR above 300 mg/g (macroalbuminuria) indicates significant kidney damage and aggressive treatment is needed.
When to Request Urgent Nephrology Referral
Refer urgently if eGFR is below 30, falling rapidly (>5 mL/min/year), or associated with significant proteinuria (urine ACR >300 mg/g). Also refer for unexplained haematuria (blood in urine), uncontrolled blood pressure despite treatment, or suspected nephrotic syndrome (oedema + heavy proteinuria + low albumin).
The Metabolic Complications of CKD
As kidney function declines, multiple metabolic disturbances occur that require their own blood test monitoring. Elevated potassium (hyperkalaemia) causes cardiac arrhythmia risk — potassium should be monitored and potassium-sparing medications adjusted accordingly. Elevated phosphate (hyperphosphataemia) in CKD stages 3–5 leads to secondary hyperparathyroidism, bone disease, and vascular calcification — managed with dietary phosphate restriction and phosphate binders. Anaemia develops as erythropoietin production falls — haemoglobin should be monitored and treated with iron, B12/folate, or erythropoiesis-stimulating agents as appropriate.
Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice. Reference ranges, supplement dosages, and nutritional information mentioned are general educational guidance from published research—not personalised recommendations. Do not use this content to self-diagnose or self-treat any condition. Always consult a qualified healthcare provider before making any changes to your health regimen, medications, or supplements.
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