Rationale for Ordering Magnesium and Albumin Laboratory Tests
Primary Clinical Rationale
Magnesium and albumin should be ordered together because approximately 25% of serum magnesium is bound to albumin, making albumin levels essential for interpreting magnesium results accurately. 1 This biochemical relationship means that hypoalbuminemia can cause falsely low total magnesium measurements even when ionized (free) magnesium—the physiologically active form—remains normal. 2, 1
When to Order These Tests
Magnesium Testing Indications
Order magnesium levels in patients with refractory hypokalemia or hypocalcemia, as magnesium deficiency prevents correction of these electrolyte abnormalities and requires magnesium repletion first. 3
Measure magnesium in critically ill patients, particularly those in intensive care units, where hypomagnesemia occurs frequently and may contribute to cardiac arrhythmias, neuromuscular irritability, and increased digoxin sensitivity. 3, 2
Check magnesium in patients with suspected esophageal perforation or other acute surgical emergencies as part of the routine electrolyte panel including sodium, potassium, chloride, magnesium, and calcium. 4
Assess magnesium in patients with liver disease, as magnesium deficiency commonly occurs due to low nutrient uptake, increased urinary losses, hypoalbuminemia, or hormone inactivation—and low magnesium can worsen liver disease progression. 5
Monitor magnesium in patients receiving medications that cause renal magnesium wasting, including loop diuretics, thiazide diuretics, aminoglycosides, cisplatin, pentamidine, and foscarnet. 3
Evaluate magnesium in alcoholic patients and diabetics, where multiple factors contribute to deficiency. 3
Albumin Testing Indications
Order albumin every 3 months in patients with chronic kidney disease (GFR <30 ml/min/1.73m²) or severe malnutrition to monitor disease severity and nutritional status, though recognize that albumin primarily reflects inflammation rather than pure nutritional status. 4, 6
Measure albumin alongside C-reactive protein (CRP) when assessing suspected malnutrition, because inflammatory cytokines directly suppress hepatic albumin synthesis even with adequate nutrition—elevated CRP indicates inflammation-driven hypoalbuminemia rather than true protein deficiency. 7, 8
Check albumin in patients with suspected protein-losing conditions including nephrotic syndrome (with urine albumin-to-creatinine ratio), protein-losing enteropathy, or severe liver disease. 7
Monitor albumin in patients with suspected esophageal perforation or acute surgical conditions as part of comprehensive metabolic assessment. 4
Critical Interpretation Principles
Magnesium Interpretation Pitfalls
A normal total serum magnesium does NOT exclude intracellular magnesium depletion, as serum levels can remain normal despite significant tissue deficiency—the majority of body magnesium resides intracellularly and in bone, not in serum. 9, 3
In critically ill patients with hypoalbuminemia, 71% of those with low total magnesium have normal ionized magnesium levels, meaning the low total magnesium is an artifact of low albumin rather than true deficiency. 2
Ionized magnesium cannot be accurately calculated from total magnesium and albumin—it must be measured directly if clinically indicated, though this is rarely necessary in routine practice. 2
The relationship between albumin and magnesium is linear at very high and very low albumin concentrations, but within the normal albumin range, magnesium concentration is independent of albumin. 1
Albumin Interpretation Pitfalls
Never interpret low albumin as malnutrition in hospitalized patients without checking inflammatory markers (CRP), as hypoalbuminemia typically reflects systemic inflammation and disease severity rather than nutritional deficiency in acute illness. 6, 7, 8
Do not order albumin infusions to "correct the number"—treat the underlying inflammatory condition or protein-losing disorder instead. 7
Albumin has a long half-life (approximately 20 days), making it insensitive for detecting acute nutritional changes—prealbumin or retinol-binding protein are superior for monitoring recent nutritional interventions. 6
Weight changes cannot be interpreted alongside albumin without assessing fluid status, as edema and ascites make both measurements unreliable in fluid-overloaded states. 6
Monitoring Frequency Algorithm
For Magnesium
Daily monitoring during initial stabilization in critically ill patients or when initiating refeeding to prevent refeeding syndrome (which includes magnesium, phosphate, and potassium depletion). 6
Every 3 months in stable chronic kidney disease patients with GFR <30 ml/min/1.73m² or severe malnutrition until stabilized. 4, 6
Reassess after correcting refractory hypokalemia or hypocalcemia to confirm magnesium repletion allowed electrolyte normalization. 3
For Albumin
Every 3 months in chronic kidney disease (GFR <30 ml/min/1.73m²) or severe malnutrition until stabilized, measuring alongside body weight. 4, 6
Every 1-3 months in chronic gastrointestinal disease with protein-losing enteropathy or malabsorption. 7
Daily to every 2-3 days in critically ill patients during initial stabilization, though recognize this primarily tracks inflammation rather than nutritional response. 6
Trigger evaluation if albumin decreases by >0.3 g/dL unintentionally—assess for underlying causes and provide dietary counseling. 6
Integration with Other Laboratory Tests
Always order magnesium as part of a comprehensive electrolyte panel including sodium, potassium, chloride, calcium, phosphate, and glucose when assessing critically ill patients or those with suspected electrolyte disturbances. 4, 6
Combine albumin measurement with complete blood count, comprehensive metabolic panel, and inflammatory markers (CRP) rather than ordering albumin in isolation. 6, 7, 8
In suspected malnutrition, order albumin alongside prealbumin, vitamin B12, folate, vitamin D, and iron studies as part of the initial nutritional assessment panel. 6, 8
For patients with liver disease, order albumin with liver function tests (bilirubin, ALT, AST) and prothrombin time to assess synthetic function comprehensively. 4