Ionised Calcium

Kidney

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Fasting Required

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Evaluates serum calcium, essential for bones, muscle function, nerve signaling, and cardiac health.

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Ionised Calcium Test Information Guide

Why is it done?
- Measures the physiologically active form of calcium in the blood - the calcium ions (Ca2+) that are not bound to proteins or complexed with other substances
- Evaluates calcium metabolism and identifies hypercalcemia or hypocalcemia when total calcium levels are unclear or misleading
- Assesses neuromuscular function, cardiac rhythm, and muscle contractility
- Ordered in critically ill patients with abnormal acid-base status, hypoalbuminemia, or renal disease where ionised calcium differs significantly from total calcium
- Monitors patients receiving blood transfusions (citrate binds ionised calcium) or receiving intravenous therapies
- Investigates symptoms of calcium imbalance such as tetany, seizures, cardiac arrhythmias, or muscle weakness
Normal Range
- Reference Range: 4.5 - 5.3 mg/dL (1.1 - 1.3 mmol/L) or 2.25 - 2.65 mEq/L
- Note: Reference ranges may vary slightly between laboratories and testing methods
- Units of Measurement: mg/dL (milligrams per deciliter), mmol/L (millimoles per liter), or mEq/L (milliequivalents per liter)
- Interpreting Results:
  - Normal: Ionised calcium is within the reference range, indicating appropriate calcium regulation and normal neuromuscular and cardiac function
  - High (Hypercalcemia): Greater than 5.3 mg/dL; indicates excessive free calcium available for biological activity
  - Low (Hypocalcemia): Less than 4.5 mg/dL; indicates insufficient free calcium for normal physiological functions
- Clinical Significance: Ionised calcium more accurately reflects the biologically active fraction than total calcium, making it essential in conditions affecting protein binding (liver disease, malnutrition) or acid-base balance
Interpretation
- Elevated Ionised Calcium (Hypercalcemia):
  - May cause polyuria, polydipsia, anorexia, nausea, vomiting, constipation, and abdominal pain
  - Can result in neuropsychiatric symptoms: confusion, lethargy, depression, and in severe cases, coma
  - Associated with cardiac arrhythmias, shortened QT interval on ECG, and decreased cardiac contractility
  - May indicate primary hyperparathyroidism, malignancy (lung, breast, lymphoma), vitamin D toxicity, sarcoidosis, or hyperthyroidism
- Decreased Ionised Calcium (Hypocalcemia):
  - Causes paresthesia, muscle cramps, tetany (involuntary muscle contractions), and seizures
  - Results in cardiac arrhythmias, prolonged QT interval, and increased risk of sudden cardiac death
  - Can be caused by hypoparathyroidism, vitamin D deficiency, renal failure, pancreatitis, or citrate toxicity from blood transfusions
  - May present with confusion, anxiety, and psychological disturbances
- Factors Affecting Ionised Calcium Levels:
  - pH and acid-base status: Alkalosis increases ionised calcium; acidosis decreases it
  - Plasma protein levels: Lower albumin reduces protein-bound calcium, potentially increasing ionised fraction
  - Medications: Citrate (transfusions), phosphate, estrogens, and thiazide diuretics affect ionised calcium
  - Magnesium and phosphate levels influence calcium ionisation and biological effects
Associated Organs
- Primary Organ Systems:
  - Parathyroid glands: Control calcium homeostasis through PTH secretion
  - Kidneys: Regulate calcium reabsorption and vitamin D metabolism
  - Gastrointestinal tract: Primary site of dietary calcium absorption under vitamin D influence
  - Bones: Act as calcium reservoir; PTH and vitamin D regulate calcium mobilization
  - Heart and nervous system: Critically depend on ionised calcium for electrical conduction and muscle function
- Conditions Associated with Abnormal Results:
  - Hypercalcemia causes: Primary hyperparathyroidism, malignancy-related hypercalcemia (PTHrP secretion), vitamin D toxicity, hyperthyroidism, sarcoidosis, tuberculosis, histoplasmosis, lymphoma, paget's disease, immobilization, and thiazide diuretic use
  - Hypocalcemia causes: Hypoparathyroidism, vitamin D deficiency, chronic kidney disease, acute pancreatitis, phosphate toxicity, loop diuretics, hypomagnesemia, hyperphosphatemia, and citrate toxicity from massive transfusion
- Potential Complications:
  - Severe hypercalcemia: Nephrogenic diabetes insipidus, acute kidney injury, cardiac arrhythmias, sudden death, hypercalcemic crisis
  - Severe hypocalcemia: Tetany, seizures, laryngospasm, respiratory failure, tetanic cardiomyopathy, sudden cardiac death
  - Chronic hypercalcemia: Nephrolithiasis, nephrocalcinosis, osteoporosis, band keratopathy, vascular calcification
Follow-up Tests
- If Hypercalcemia Detected:
  - Total serum calcium: Confirm elevated ionised calcium corresponds to elevated total calcium
  - Parathyroid hormone (PTH): Differentiate between PTH-mediated and non-PTH-mediated hypercalcemia
  - 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D: Assess vitamin D-mediated hypercalcemia
  - PTHrP (parathyroid hormone-related peptide): Screen for malignancy-related hypercalcemia
  - Serum phosphate: Assess kidney function and PTH effectiveness
  - Creatinine and BUN: Evaluate renal function and degree of dehydration
  - 24-hour urine calcium: Assess magnitude of hypercalcemia and rule out familial hypocalciuric hypercalcemia
  - Chest X-ray or CT imaging: Rule out sarcoidosis, lymphoma, or other malignancies
  - ECG: Assess for shortened QT interval and cardiac arrhythmias
- If Hypocalcemia Detected:
  - Total serum calcium: Confirm ionised calcium abnormality
  - Parathyroid hormone (PTH): Determine if hypoparathyroidism or secondary hyperparathyroidism
  - 25-hydroxyvitamin D: Screen for vitamin D deficiency
  - Magnesium: Hypomagnesemia impairs PTH secretion and action; may be underlying cause
  - Serum phosphate: Elevated in chronic kidney disease and hypoparathyroidism
  - Creatinine and BUN: Assess renal function
  - Albumin: Low levels may contribute to low ionised calcium
  - Lipase and amylase: Rule out acute pancreatitis
  - ECG: Monitor for prolonged QT interval and arrhythmias
- Monitoring Frequency:
  - Critical/ICU patients: Repeat ionised calcium every 4-6 hours or more frequently if receiving interventions
  - Post-transfusion or massive fluid resuscitation: Check ionised calcium after significant blood product administration
  - Chronic conditions: Monitor every 3-6 months based on underlying disorder and treatment response
  - Post-treatment: Follow-up testing to ensure normalization after intervention (e.g., PTH surgery, vitamin D supplementation)
Fasting Required?
- Fasting Requirement: No - Fasting is NOT required for ionised calcium testing
- Patient Preparation:
  - Patient may eat and drink normally prior to testing
  - No need to fast overnight or avoid specific foods or beverages
  - Patient should be calm and seated for 5 minutes before blood draw to minimize stress-related changes
- Special Specimen Collection Considerations:
  - CRITICAL: Blood must be collected ANAEROBICALLY (without air) to prevent CO2 loss, which would alter pH
  - Use heparinized collection tubes (not EDTA, citrate, or serum separator tubes) as specified by laboratory
  - Specimen must be transported to laboratory immediately on ice to maintain physiological conditions
  - Analysis should occur within 15-30 minutes of collection to prevent falsely low values due to continued cellular metabolism
  - If on mechanical ventilation, document current pH and respiratory settings as these significantly influence results
- Medications and Supplements:
  - Continue taking all medications as normally prescribed unless specifically instructed otherwise by healthcare provider
  - Inform laboratory and healthcare provider of current medications, especially thiazide diuretics, vitamin D supplements, calcium supplements, corticosteroids, and loop diuretics
  - Do NOT stop medications before the test without explicit instructions, as abrupt discontinuation may alter results

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