How to Use This Page
Use this as a quick guide for interpreting U&Es and related electrolytes at the bedside. Always interpret results with the clinical picture and local lab reference ranges.
Electrolytes & Renal Panel (including Ca / Mg / Phosphate)
| Parameter | High Value | Low Value | Common Causes of High | Common Causes of Low |
|---|---|---|---|---|
| Sodium (Na⁺) | Hypernatremia | Hyponatremia |
Dehydration, diabetes insipidus, osmotic diuresis, excessive salt intake, hyperaldosteronism. |
SIADH, heart failure, liver cirrhosis, nephrotic syndrome, excess free water, thiazides, adrenal insufficiency. |
| Potassium (K⁺) | Hyperkalemia ECG risk | Hypokalemia ECG risk |
Renal failure, ACEi/ARB, spironolactone, potassium supplements, acidosis, cell lysis (rhabdo, tumour lysis), Addison's disease. |
Diuretics, vomiting/diarrhoea, insulin + glucose, β-agonists, hyperaldosteronism, alkalosis, poor intake. |
| Chloride (Cl⁻) | Hyperchloremia | Hypochloremia |
Normal saline overload, dehydration, renal tubular acidosis, diarrhoea, metabolic acidosis. |
Vomiting, gastric losses, diuretics, metabolic alkalosis, heart failure. |
| Bicarbonate (HCO₃⁻) | High HCO₃⁻ | Low HCO₃⁻ |
Metabolic alkalosis (vomiting, diuretics), chronic CO₂ retention (COPD), volume depletion with contraction alkalosis. |
Metabolic acidosis (DKA, sepsis, renal failure, lactic acidosis), diarrhoea, renal tubular acidosis. |
| Urea / BUN | Increased urea (BUN) | Decreased urea |
Pre-renal azotaemia: dehydration, shock, GI bleed; renal failure; high protein intake; catabolic states. |
Severe liver disease, low protein intake, overhydration, late pregnancy. |
| Creatinine | Increased creatinine | Decreased creatinine |
Acute or chronic kidney disease, obstruction, nephrotoxins, rhabdomyolysis, hypotension/shock. |
Low muscle mass (elderly, cachexia), pregnancy, amputations, malnutrition. |
| Calcium (Ca²⁺) | Hypercalcemia | Hypocalcemia |
Primary hyperparathyroidism, malignancy (bone mets, myeloma, PTHrP), vitamin D excess, thiazides, prolonged immobilisation. |
Hypoparathyroidism, vitamin D deficiency, chronic kidney disease, pancreatitis, massive transfusion (citrate). |
| Magnesium (Mg²⁺) | Hypermagnesemia | Hypomagnesemia |
Renal failure, excess Mg-containing antacids/laxatives, iatrogenic over-replacement. |
Malnutrition, alcoholism, chronic diarrhoea, diuretics, diabetes, PPIs, burns. |
| Phosphate (PO₄³⁻) | Hyperphosphatemia | Hypophosphatemia |
Chronic kidney disease, tumour lysis, rhabdomyolysis, hypoparathyroidism, vitamin D excess. |
Malnutrition/refeeding, alcoholism, DKA treatment, hyperparathyroidism, diarrhoea, diuretics. |
Tip: Always look at trends, not single values, and correlate with the ABG, fluid balance, and ECG (especially for K⁺, Ca²⁺, Mg²⁺).
Chronic Kidney Disease – GFR-Based Staging
Staging is based on estimated GFR (eGFR). Creatinine values below are rough guides and will vary with lab, muscle mass, sex, and age. Use your lab’s eGFR where available.
| Stage | eGFR (ml/min/1.73 m²) | Typical Description | Approx. Creatinine (µmol/L) | Approx. Creatinine (mg/dL) |
|---|---|---|---|---|
| G1 | > 90 | Normal or high GFR (with other markers of kidney damage) | < ~104 | < ~1.2 |
| G2 | 60–89 | Mildly decreased GFR | ~104–159 | ~1.2–1.8 |
| G3a | 45–59 | Mild–moderate decrease | ~159–200 | ~1.8–2.3 |
| G3b | 30–44 | Moderate–severe decrease | ~200–309 | ~2.3–3.5 |
| G4 | 15–29 | Severely decreased | ~309–440 | ~3.5–5.0 |
| G5 | < 15 | Kidney failure (end-stage) | > ~440 | > ~5.0 |
Practical ED use: Think “GFR < 30” (G4–G5) as a red flag for: dose-adjustment or avoidance of renally-cleared drugs, risk of volume overload, and need for urgent senior/nephrology input.