Reliability of Serum Calcium to Phosphorus (Ca/P) Ratio as an Accurate and Inexpensive Tool to Define Disorders of Ca-P Metabolism

Serum Calcium to Phosphorus (Ca/P) Ratio to Define Disorders of Ca-P Metabolism

BACKGROUND: Primary hyperparathyroidism (PHPT) is the third most common endocrine disorder. The Ca/P ratio is an accurate tool to differentiate patients with PHPT (>3.5 if Ca and P are expressed in mg/dl) from healthy subjects. The reliability of this index is based on the fact that serum Ca and P are inversely related together. However, other disorders of the Ca-P metabolism, such as hypophosphoremia (HypoP) not related to PHPT, might also impair the Ca/P ratio.

OBJECTIVE: To validate the accuracy of Ca/P ratio in the diagnosis of Ca-P metabolism disorders, including also patients with documented HypoP not related to PHPT.

METHODS: A single-center, retrospective, case-control study will be carried out.

Biochemical measurements will include parathormone (PTH), vitamin D, serum Ca and P, serum albumin and creatinine.

Inclusion Criteria:

• patients with diagnosis of primary hyperparathyroidism
• HIV-infected patients with reduced phosphorus but normal calcium
• subjects with normal Calcium-Phosphorus metabolism

Exclusion criteria for both cases and controls will be:

• age younger than 18 or older than 90 years
• severe renal and liver diseases (i.e. glomerular filtration rate (GFR) <30 ml/min)
• hyperparathyroidism secondary to Vitamin D deficiency
• active metabolic bone disease (e.g. Paget's disease of the bone, osteomalacia, rickets, etc)
• any type of cancer
• malnutrition
• severe obesity (BMI > 40 kg/m2)
• a history of gastrointestinal malabsorption
• sarcoidosis
• hypercortisolism
• diabetes insipidus
• hyperthyroidism
• pseudohypoparathyroidism
• familial hypocalciuric hypercalcemia (FHH)
• treatment with steroids, active forms of vitamin D (calcitriol, ergocalciferol, etc), thiazides, phosphate binders, lithium, cinacalcet, bisphosphonates, and denosumab.