Why is calcium level checked in patients with secondary hypertension?

Calcium Screening in Secondary Hypertension

Calcium levels are checked in secondary hypertension evaluation primarily to screen for hyperparathyroidism, which can cause hypertension through calcium-mediated vascular effects and is a treatable cause of high blood pressure. 1

Rationale for Calcium Testing

Calcium testing is an essential component of the secondary hypertension workup for several reasons:

1. Hyperparathyroidism Detection:

   • Primary hyperparathyroidism can cause hypertension and is included in standard screening protocols for secondary hypertension 1
   • The European Society of Cardiology explicitly lists parathyroid hormone and calcium/phosphate testing as recommended screening tests for hyperparathyroidism as a cause of secondary hypertension 1

2. Prevalence Considerations:

   • While the exact prevalence varies, hyperparathyroidism is found in approximately 1 in 130 hypertensive patients, which is significantly higher than in the general population (1 in 1,000-2,000) 2
   • This makes calcium screening a high-yield test in the hypertension workup

3. Pathophysiological Mechanism:

   • Hypercalcemia can directly cause blood pressure elevation through vascular smooth muscle effects 3
   • Parathyroid hormone may play a permissive role in the hypertensive action of hypercalcemia 3

When to Check Calcium Levels

Calcium screening should be performed in patients with:

• Early-onset hypertension (<30 years of age) 1
• Resistant hypertension (BP not controlled on ≥3 medications) 1
• Sudden deterioration in previously well-controlled BP 1
• Hypertensive urgency or emergency 1
• Clinical features suggesting secondary causes 1
• Severe hypertension (≥180/110 mmHg) 1

Diagnostic Approach

When checking calcium levels:

1. Initial Testing:

   • Serum calcium should be part of the basic biochemistry panel 1, 4
   • Interpret calcium results in conjunction with phosphate levels 1

2. Follow-up Testing:

   • If calcium is elevated, measure parathyroid hormone (PTH) levels 1, 4
   • Normal calcium with high-normal PTH may still indicate secondary hyperparathyroidism due to insufficient calcium intake 5

3. Confirmatory Testing:

   • Calcium challenge test may be useful to confirm secondary hyperparathyroidism in cases with normal-low calcium and elevated PTH 5

Clinical Implications

The identification of hyperparathyroidism through calcium screening has important clinical implications:

• Treatment Impact: Parathyroidectomy in patients with primary hyperparathyroidism can improve both hypertension and glucose control in some patients 6
• Preventing Complications: Early detection and treatment may prevent renal damage 2
• Medication Adjustment: Some patients may require fewer antihypertensive medications after correction of hyperparathyroidism 6

Pitfalls to Avoid

• Overlooking normal-low calcium: Even with normal-low calcium levels, elevated PTH may indicate secondary hyperparathyroidism 5
• Failing to correct calcium: Albumin-corrected calcium should be used for accurate interpretation
• Isolated testing: Calcium should be interpreted alongside phosphate and PTH levels for complete evaluation 1
• Ignoring medication effects: Some medications can affect calcium levels and should be considered when interpreting results

By including calcium testing in the evaluation of secondary hypertension, clinicians can identify potentially treatable causes and improve patient outcomes through targeted interventions.