Reliability of calcium–phosphorus (Ca/P) ratio as a new, accurate and inexpensive tool in the diagnosis of some Ca–P disorders

• Published in: Journal of endocrinological investigation Vol. 42; no. 9; pp. 1041 - 1049
• Main Authors: Madeo, B., De Vincentis, S., Kara, E., Vescini, F., Trenti, T., Guaraldi, G., Rochira, V.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.09.2019; Springer Nature B.V
• Subjects: Adult; Aged; Aged, 80 and over; Biomarkers - metabolism; Calcium; Calcium (blood); Calcium - metabolism; Case-Control Studies; Creatinine; Diagnosis; Endocrinology; Female; Follow-Up Studies; HIV; HIV - isolation & purification; HIV Infections - complications; HIV Infections - metabolism; HIV Infections - virology; Human immunodeficiency virus; Humans; Hyperparathyroidism; Hyperparathyroidism, Primary - complications; Hyperparathyroidism, Primary - diagnosis; Hyperparathyroidism, Primary - metabolism; Hypophosphatemia; Hypophosphatemia - complications; Hypophosphatemia - diagnosis; Hypophosphatemia - metabolism; Male; Medicine; Medicine & Public Health; Metabolic Diseases; Metabolism; Middle Aged; Original Article; Parathyroid; Parathyroid hormone; Phosphorus; Phosphorus - metabolism; Prognosis; Reproducibility of Results; Retrospective Studies; Vitamin D; Young Adult; Screening; Hypophosphatemia; Calcium–phosphorus metabolism; Hyperparathyroidism
• DOI: 10.1007/s40618-019-01025-6
• ISSN: 1720-8386; 0391-4097

Purpose The serum calcium/phosphorus (Ca/P) ratio is an accurate tool to differentiate patients with primary hyperparathyroidism (PHPT) from healthy subjects. However, other disorders of the Ca–P metabolism might impair the Ca/P ratio, such as hypophosphatemia (HypoP) not PHPT related. The aim of this study is to examine the diagnostic value of Ca/P ratio in the diagnosis of PHPT and HypoP not PHPT related. Methods Single-center, retrospective, case–control study, including 150 patients with PHPT and 306 patients with HypoP, compared with 150 controls. HypoP patients were enrolled among HIV-infected patients by selecting those with Fanconi-like syndrome due to antiretroviral treatment. Parameters which were measured were serum Ca, P, parathyroid hormone (PTH), 25-OH vitamin D, albumin and creatinine). Results The Ca/P ratio was significantly higher in PHPT and HypoP patients, compared to controls ( p  < 0.0001). At receiver operator characteristic (ROC) curve analysis, the cut-off of 3.56 (2.75 SI) for Ca/P ratio was able to identify patients with PHPT and HypoP (sensitivity 95%; specificity 93%). Among patients with Ca/P ratio above 3.56, the thresholds of 10.3 mg/dL (2.6 mmol/L) for serum Ca (sensitivity 93%; specificity 98%) and 80.5 pg/mL for PTH (sensitivity 91%; specificity 91%) were defined for the specific diagnosis of PHPT. Conclusions The Ca/P ratio above 3.56 (2.75 SI) is a highly accurate tool to identify PHPT and HypoP not PHPT-related patients. Thanks to its simplicity, this index can be proposed as a screening and first-line examination in the diagnostic work-up when a disorder of Ca–P metabolism is suspected or should be ruled out.