New parathyroid function index for the differentiation of primary and secondary hyperparathyroidism: a case-control study

Abstract

Background: Patients with primary hyperparathyroidism (PHPT) may be asymptomatic, and some may present with normocalcemic PHPT (NPHPT). Patients with vitamin D deficiency may also be asymptomatic, with normal calcium and elevated PTH concentrations. These latter patients are usually diagnosed with vitamin D deficiency-induced secondary hyperparathyroidism (VD-SHPT). Therefore, it is very difficult to distinguish PHPT and NPHPT from VD-SHPT based on calcium or PTH concentrations in clinical settings. In this case-control study, we aimed to verify the diagnostic power of a new parathyroid function index (PFindex = Ca*PTH/P). Methods: This study enrolled 128 patients with surgically and pathologically confirmed PHPT, including 36 with NPHPT, at a hospital in West China between January 2009 and September 2017. Thirty-seven patients with VD-SHPT and 45 healthy controls were selected from the population of a cross-sectional epidemiological study as the SHPT and healthy groups, respectively. We used the PFindex to describe the characteristics of PHPT, NPHPT, and VD-SHPT.. Differences between the four groups were compared, and a receiver operating characteristic (ROC) curve analysis was used to evaluate the diagnostic power of PFindex. Results: The PHPT group had the highest PFindex (454 ± 430), compared to the other three groups (NPHPT: 101 ± 111; SHPT: 21.7 ± 6.38; healthy: 12.2 ± 2.98, all p < 0.001). A PFindex cutoff value of 34 yielded sensitivity and specificity rates of 96.9 and 97.6% and of 94.4 and 94.6% for the diagnoses of PHPT and NPHPT, respectively. The use of a PFindex > 34 to differentiate NPHPT from VD-SHPT yielded the highest positive likelihood ratio and lowest negative likelihood ratio. Conclusion: The PFindex provided excellent diagnostic power for the differentiation of NPHPT from VD-SHPT. This simple tool may be useful for guiding timely decision-making processes regarding the initiation of vitamin D treatment or surgery for PHPT.

Normocalcemic Hyperparathyroidism: A Heterogeneous Disorder Often Misdiagnosed?

“…Guo and colleagues ( 15 ) proposed another simple ratio called the PFindex to discriminate PHPT from vitamin D‐deficient secondary hyperparathyroidism. This index was defined as serum Ca × PTH/P, with Ca and P reported in mmol/L, and PTH in pg/mL.…”

Comparisons Between Normocalcemic Primary Hyperparathyroidism and Typical Primary Hyperparathyroidism

“…Since the negative predictive value was high (88%) in the study, the Ca/P ratio may be more useful to rule out NPHPT. Guo et al 4 proposed a parathyroid function index to be a reliable tool for distinguishing true NPHPT from vitamin D-deficient secondary hyperparathyroidism. Lavryk et al 5 presented the nomogram using Ca and PTH to distinguish healthy individuals from diseased patients, particularly those presenting atypical forms of PHPT.…”

Diagnostic performance of the calcium/phosphate ratio for primary hyperparathyroidism in southwest China

“…The mechanism is as follows: (1) PTH directly increases calcium absorption and decreases phosphate reabsorption in the proximal tubule of the kidney; (2) PTH promotes the conversion of 25(OH) vitamin D to 1,25-dihydroxyvitamin D by increasing the activity of 1α-hydroxylase in the proximal tubule of the kidney, which promotes gut calcium and phosphate absorption. Although other studies have already investigated the Ca/P ratio in the diagnosis of PHPT, they did not compare the Ca/P ratio with the Cl/P ratio ( 13 , 23 , 24 , 25 ). In another study by Madeo et al , the cut-off Ca/P value of 2.55 was able to correctly identify 101 out of 142 NPHPT patients, showing a high sensitivity (71.1%) and specificity (87.9%), which is in line with our findings ( 13 ).…”