Is a parathyroid lab test typically included in a comprehensive metabolic panel (CMP) or endocrine panel?

Parathyroid Hormone Testing is NOT Included in Standard Laboratory Panels

Parathyroid hormone (PTH) is not included in either a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP) and must be ordered as a separate, specific test. 1

What Standard Panels Actually Include

Comprehensive Metabolic Panel (CMP) Components

• Serum calcium is included in the CMP, which can suggest parathyroid dysfunction when abnormal 1
• Serum phosphorus is included, which may be low in primary hyperparathyroidism 2
• Alkaline phosphatase is included, which can be elevated in hyperparathyroid bone disease 1
• Kidney function markers (creatinine, BUN) are included, which are essential for interpreting PTH levels 1, 2

What Requires Separate Ordering

• Intact PTH (iPTH) must be specifically ordered as a standalone test 1, 2
• 25-hydroxyvitamin D requires separate ordering and is crucial for interpreting PTH results 2
• 24-hour urine calcium requires separate collection when evaluating parathyroid disorders 2

Clinical Algorithm for When to Order PTH

Screening Indications for PTH Testing

• Hypercalcemia detected on CMP: Order intact PTH immediately to differentiate primary hyperparathyroidism from other causes 2, 3
• Chronic kidney disease with GFR <60 mL/min/1.73 m²: Measure calcium, phosphorus, and intact PTH to monitor for secondary hyperparathyroidism 1, 4
• Unexplained hypocalcemia: Order PTH to distinguish hypoparathyroidism from other causes 5, 3
• Metabolic bone disease evaluation: PTH is essential when investigating osteoporosis, bone pain, or fractures 6

The Diagnostic Sequence

1. Initial CMP reveals abnormal calcium → Order intact PTH simultaneously with 25-hydroxyvitamin D 2
2. Elevated calcium + elevated or inappropriately normal PTH = Primary hyperparathyroidism 2, 3
3. Normal/low calcium + elevated PTH = Secondary hyperparathyroidism (check vitamin D and kidney function) 3
4. Low calcium + low PTH = Hypoparathyroidism 5, 3

Critical Technical Considerations

PTH Assay Variability

• Different assay generations measure different PTH fragments, with second-generation assays overestimating biologically active PTH by detecting inactive 7-84 fragments 1, 4
• Third-generation assays are more specific for full-length 1-84 PTH but are not yet universally standardized 1, 4
• Sequential measurements must use the same assay in the same laboratory to ensure accurate trend evaluation 1
• Interlaboratory variability can reach 47% even within the same assay generation due to lack of standardization 1, 4

Sample Collection Requirements

• EDTA plasma is preferred over serum for PTH measurement as PTH is most stable in EDTA 2
• Storage at 4°C is superior to room temperature for maintaining PTH stability 2
• Biotin supplements can interfere with PTH assays, leading to falsely high or low results depending on assay design 2

Common Clinical Pitfalls

Interpretation Errors to Avoid

• Never interpret PTH without knowing vitamin D status: Vitamin D deficiency can elevate PTH and mask primary hyperparathyroidism or suppress urine calcium excretion 2
• Do not target "normal" PTH ranges in CKD patients: Attempting to maintain PTH <65 pg/mL in CKD can cause adynamic bone disease; use stage-specific targets instead 4
• Recognize that PTH increases with age, BMI, and varies by race: Black individuals have 20% higher PTH levels, and PTH rises with declining GFR 2

When Standard Panels Are Insufficient

• A normal CMP does not exclude normocalcemic hyperparathyroidism, which requires specific PTH measurement for diagnosis 2, 6
• Bone health screening panels that include PTH, calcium, and vitamin D together identify 68% of patients with abnormal PTH secretion that would be missed by CMP alone 6