Bone and Mineral Metabolism

SAT-822 - Clinical Predictors of Response to Oral Calcium Suppression Testing in Differentiating Secondary and Primary Normocalcemic Hyperparathyroidism

Saturday, June 13, 2026

9:30 AM - 4:30 PM CT

Location: ENDOExpo; Poster Floor

Abstract Poster Presenter(s)

Malini Ganesh, MD

Physician
North Atlanta Endocrinology & Diabetes PC
Suwanee, GA, United States

Senior Author/Primary Investigator(s)

Malini Ganesh, MD

Physician
North Atlanta Endocrinology & Diabetes PC
Suwanee, GA, United States
SB

Sanford Baim, FACR, CCD

Professor of Medicine
Rush University Medical Center and Cook County Health System Rush University Medical Center
Chicago, United States

Co-Author(s)

MT

Merih Tesfazghi, PhD, DABCC

Director, Rush Core Laboratory and Point of Care Testing
Rush University Medical Center
Chicago, Illinois, United States
SN

Sandra Naaman, MD, PhD, FACP

Assistant Professor of Medicine
Rush University Medical Center
Chicago, United States
SB

Sanford Baim, FACR, CCD

Professor of Medicine
Rush University Medical Center and Cook County Health System Rush University Medical Center
Chicago, United States

Disclosure(s):

Malini Ganesh, MD: No financial relationships to disclose

Background: Guidelines for management of normocalcemic primary hyperparathyroidism (NPHPT) are lacking due to the absence of both a universally accepted definition and evidence‑based treatment criteria. The bone profile of NPHPT patients has been reported to range from normal to that observed in classic PHPT, complicating differentiation from secondary hyperparathyroidism (SHPT). To address this diagnostic challenge, a clinician conducted a real‑world calcium‑suppression study in a metabolic‑bone clinic from 2015 to 2023. Participants were given 1,200 mg–1,500 mg of elemental calcium daily, with the dosing individualized based on tolerance, interacting medications, and overall medical history.
INCLUSION CRITERIA: Eligible participants were adults aged ≥ 18 years of age with BMI 18‑38 kg/m², eGFR ≥ 45 mL/min/1.73 m², and normal 25‑OH vitamin D, phosphate, magnesium, adjusted total calcium, and ionized calcium. All had elevated iPTH (Abbott, Roche, or Siemens) and no prior history of hypercalcemia or PHPT. iPTH, calcium, fracture history, bone density scan (DXA) results, and vitamin D levels were confirmed via EMR review by two clinicians. Fracture Risk Assessment (FRAX) was manually calculated at the initial visit. Of 350 screened patients, 97 met criteria for NPHPT. A positive calcium‑suppression test (consistent with secondary hyperparathyroidism) was defined as 1) normalization of iPTH that persisted throughout the study, or 2) an iPTH drop exceeding the median reference‑change value (RCV) of ± 29.5 %. Univariate and multivariate analyses identified predictors of the calcium‑challenge response, expressed as Δ PTH.

Results: After the calcium challenge, both the NPHPT and SHPT groups showed a significant rise in total 25‑(OH)D compared with baseline. However, the SHPT cohort exhibited a stronger response to the calcium challenge, characterized by greater reductions in PTH and higher adjusted serum calcium post challenge. At baseline, fragility fractures were present in 31 % of NPHPT patients and 48 % of SHPT patients, while osteoporosis on DXA was found in 62.5 % of NPHPT and 53.3 % of SHPT participants. 50% of patients with NPHPT met WHO criteria for high fracture risk. In univariate analyses, the change in adjusted calcium (Δ Ca) from pre‑ to post‑challenge was an inverse predictor of the change in PTH (Δ PTH) for both groups. Multivariate analysis confirmed that Δ Ca remained a significant inverse predictor of Δ PTH in the NPHPT group with a similar trend toward significance observed in the SHPT group.

Conclusion: In this real-world cohort, the majority of NPHPT patients had clinical or DXA-defined osteoporosis, at rates higher than previously reported. The increase in calcium levels following a calcium suppression test, predicted subsequent decline in PTH, supporting the utility of of this test in distinguishing NPHPT from SHPT and characterizing skeletal risk.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*