Reliability of calcium–phosphorus (Ca/P) ratio as a new, accurate and inexpensive tool in the diagnosis of some Ca–P disorders
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.
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).
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.
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.
KeywordsCalcium–phosphorus metabolism Hyperparathyroidism Hypophosphatemia Screening
B. Madeo is the Principal Investigator and conceived the study, analysed the data, provided data interpretation and wrote the manuscript. S. De Vincentis collected and analyzed the data, and wrote the manuscript. E. Kara collected clinical and biochemical data. F. Vescini contributed to conceive the study. T. Trenti provided data about laboratory assays. G. Guaraldi provided clinical and biochemical data about HypoP patients. V. Rochira conceived the study, analysed the data, provided data interpretation and wrote the manuscript. All authors approved the final version of the manuscript and fully contributed to its final version.
This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained for all individual participant included in the study.
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