Chart — Renal
Renal Lab Values Chart
Quick-reference renal laboratory values — BUN, creatinine, eGFR, urine studies, electrolytes, and urinalysis casts: normal ranges, elevated and decreased causes, and key clinical flags.
Source: KDIGO 2012/2022 AKI and CKD Guidelines; National Kidney Foundation KDOQI Guidelines; Clinical laboratory references. Ranges reflect typical adult values — verify with institutional norms.
Educational use only. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Lab interpretation tip:Renal labs must be interpreted as a set. A rising creatinine with BUN:Cr >20:1 points to prerenal; a normal ratio with granular casts on UA points to ATN. No single lab tells the full story.
Kidney Function Markers
| Lab Test | Normal Range | Elevated Causes | Decreased Causes |
|---|---|---|---|
| BUN (Blood Urea Nitrogen) | 7–20 mg/dL | AKI, CKD, prerenal azotemia (dehydration/shock), GI bleeding, high protein diet, steroids, catabolism (sepsis, burns) | Liver failure (↓ urea synthesis), malnutrition, overhydration, pregnancy |
| ★ Less specific than creatinine — always interpret with creatinine and clinical context | |||
| Serum Creatinine | 0.6–1.2 mg/dL (M); 0.5–1.1 mg/dL (F) | AKI, CKD, rhabdomyolysis, high meat diet. Doesn't rise until ~50% of nephrons lost. | Low muscle mass (elderly, cachexia, amputee), pregnancy |
| ★ DOUBLES when GFR falls by ~50%. Best single serum marker of GFR. | |||
| BUN:Creatinine Ratio | 10:1 to 20:1 | >20:1 = prerenal AKI (dehydration, HF, shock, GI bleed, high protein) — kidneys retaining urea | <10:1 = intrarenal (tubular) damage, liver failure, malnutrition |
| ★ NCLEX gold standard: BUN:Cr >20:1 = prerenal (volume problem) | |||
| eGFR | ≥90 mL/min/1.73m² | Hyperfiltration (early diabetes, obesity) — not clinically significant | Any fall = AKI acutely. <60 for ≥3 months = CKD. Stage G5 (<15) = ESRD requiring dialysis. |
| ★ Calculated from creatinine, age, sex. Best overall kidney function test. | |||
Urine Studies
| Lab Test | Normal Range | Elevated Causes | Decreased Causes |
|---|---|---|---|
| Urine Specific Gravity | 1.003–1.030 | >1.030: concentrated — dehydration, SIADH, adrenal insufficiency, prerenal AKI (compensatory concentration) | <1.003: dilute — diabetes insipidus, overhydration, ATN (tubular damage) |
| ★ Fixed 1.010 (isosthenuria) = severe tubular damage — ATN hallmark | |||
| Urine Output | ≥0.5 mL/kg/hr (minimum 30 mL/hr) | Polyuria (>3 L/day): DI, osmotic diuresis, diuretics, post-obstructive diuresis, ATN recovery | Oliguria (<0.5 mL/kg/hr): AKI, shock, HF, obstruction. Anuria (<50 mL/day) = emergency. |
| ★ UO <30 mL/hr = report immediately in all clinical settings | |||
| FENa (Fractional Excretion of Sodium) | N/A — diagnostic ratio | >2%: intrarenal damage (ATN) — tubules cannot reabsorb Na. Also: chronic CKD, diuretic use (invalidates FENa). | <1%: prerenal (kidneys aggressively retaining Na) or hepatorenal syndrome |
| ★ Invalid if patient received diuretics — use FEUrea instead | |||
| Urine Protein (Dipstick / UACR) | Negative to trace (dipstick); UACR <30 mg/g | Glomerular disease (nephrotic: >3.5 g/day), diabetic nephropathy (microalbuminuria = 30–300 mg/g UACR), CKD, preeclampsia, HF | Not clinically significant when decreased |
| ★ Microalbuminuria (UACR 30–300) = earliest sign of diabetic nephropathy | |||
Electrolytes in Kidney Disease
| Lab Test | Normal Range | Elevated Causes | Decreased Causes |
|---|---|---|---|
| Serum Potassium (K⁺) | 3.5–5.0 mEq/L | Hyperkalemia: AKI, CKD (↓ excretion), acidosis (H⁺ drives K⁺ out of cells), tissue necrosis, ACE inhibitors/ARBs, K⁺-sparing diuretics, hemolysis (specimen), rhabdomyolysis | Hypokalemia: loop diuretics (furosemide), vomiting, diarrhea, alkalosis |
| ★ K⁺ >6.0 = EMERGENCY. ECG: peaked T waves → widened QRS → sine wave → VF. Treat immediately. | |||
| Serum Phosphorus | 2.5–4.5 mg/dL | Hyperphosphatemia: AKI, CKD (kidneys cannot excrete PO₄), hypoparathyroidism, rhabdomyolysis, tumor lysis syndrome | Hypophosphatemia: malnutrition, refeeding syndrome, antacid use, alcoholism, hyperparathyroidism |
| ★ In CKD: hyperphosphatemia + hypocalcemia = renal osteodystrophy. Treat with phosphate binders with meals. | |||
| Serum Calcium (Ca²⁺) | 8.5–10.5 mg/dL total; ionized 4.6–5.3 mg/dL | Hypercalcemia: hyperparathyroidism, malignancy, immobility, thiazide diuretics, excess vitamin D, Paget disease | Hypocalcemia: AKI/CKD (↓ vitamin D activation, hyperphosphatemia binds Ca²⁺), hypoparathyroidism, pancreatitis, hypomagnesemia |
| ★ Correct for albumin: add 0.8 mg/dL for each 1 g/dL decrease in albumin below 4.0 | |||
| Serum Bicarbonate (HCO₃⁻) | 22–29 mEq/L | Metabolic alkalosis: vomiting (HCl loss), loop diuretics, hyperaldosteronism, excessive bicarb administration | Metabolic acidosis: AKI, CKD (↓ H⁺ excretion, ↓ NH₃ production), DKA, lactic acidosis, diarrhea, RTA |
| ★ CKD metabolic acidosis: bicarb <22 = start sodium bicarbonate supplementation | |||
Urinalysis Casts (Microscopy)
| Lab Test | Normal Range | Elevated Causes | Decreased Causes |
|---|---|---|---|
| Hyaline casts | 0–1/hpf (normal in concentrated urine or after exercise) | Concentrated urine, fever, strenuous exercise, mild prerenal azotemia | Not clinically significant when absent |
| ★ Least specific cast — may be normal | |||
| Granular (muddy-brown) casts | Absent | ATN (acute tubular necrosis) — cellular debris from damaged tubular epithelial cells | N/A |
| ★ NCLEX: Muddy-brown granular casts = ATN. Pathognomonic for intrinsic tubular damage. | |||
| RBC casts | Absent | Glomerulonephritis (GN) — bleeding within glomeruli; post-streptococcal GN, IgA nephropathy, lupus nephritis, Goodpasture syndrome | N/A |
| ★ RBC casts = glomerular bleeding = GN until proven otherwise | |||
| WBC casts | Absent | Pyelonephritis (upper UTI), acute interstitial nephritis (AIN — drug hypersensitivity), glomerulonephritis with WBC response | N/A |
| ★ WBC casts = kidney inflammation. Differentiate: AIN (drug exposure history) vs pyelonephritis (fever, CVA tenderness) | |||
Related Resources
Renal Laboratory Values ReferenceDetailed interpretation notes for each renal lab test
Open →Urine Assessment ReferenceUrine color, clarity, odor, specific gravity, and output
Open →Acute Kidney Injury (AKI)Lab patterns in AKI: BUN:Cr ratio, FENa, casts
Open →Chronic Kidney Disease (CKD)Lab trends in CKD: anemia, electrolytes, bone disease
Open →AKI vs CKD Comparison ChartSide-by-side: onset, reversibility, and lab findings
Open →Standards & sources
Fact-checked Jun 21, 2026This page is written to align with KDIGO AKI/CKD Guidelines; National Kidney Foundation KDOQI; Clinical laboratory references. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →