Intended for Healthcare Professionals
You are here
Home > Medical Calculator > Parathyroid Scan Score Calculator

Parathyroid Scan Score Calculator (Revised 2020)

basal metabolic rate


Developed by Dr. Thanh D. Hoang, DO. Division of Endocrinology, Walter Reed National Military Medical Center, 8901 Wisconsin Avenue, Bethesda, MD 20889.

     Primary hyperparathyroidism (PHPT) is a common disorder of the inappropriate secretion of parathyroid hormone (PTH) from one or more of the parathyroid glands, leading to hypercalcemia. PHPT is often discovered incidentally; the majority of cases arise from a single parathyroid adenoma, whereas 15% arise from hyperplastic glands. Most of the patients with PHPT are asymptomatic, but many may present with nephrolithiasis, decreased bone mass, or nonspecific symptoms such as weakness, fatigue, neuromuscular dysfunction, cardiovascular effects, and neuropsychiatric problems that may improve after parathyroidectomy.

      Prior to the advent of the technetium-99 sestamibi (99mTc) parathyroid scan, patients with PHPT underwent surgical bilateral neck exploration to assess all 4 parathyroid glands, which can be a long and tedious surgical procedure. The 99mTc scan was introduced in the early 1990s and has become a popular preoperative test to localize a parathyroid adenoma with a reported sensitivity of 75 to 100% and a positive predictive value of 89 to 96% (1).

     There are no well-established biochemical markers to predict the probability of a positive 99mTc scan in patients with PHPT. In an original paper, Hoang et al (2) found that there are significant associations between the levels of serum ionized calcium, phosphate, intact PTH, and 99mTc scan positivity. Based on the findings of this study, Hoang et al (2) have developed this quick calculator to estimate the probability of having a positive 99mTc scan prior to surgery.

    This calculator has several advantages: (1), if the score is high, the probability of localization of a parathyroid adenoma is high and this can facilitate a parathyroidectomy for surgeons, (2), if the score is low, clinicians may not need to obtain the 99mTc scan because the probability of localization is low; therefore, patients may not require surgery at this time and may need surveillance follow-up, (3), the calculator is quick and easy and can be accessible anywhere, (4), the calculator is cost-saving ($550.00 per 99mTc scan; $100-$1,000.00 per thyroid ultrasound; $6,773.00 per 4-dimensional computed tomography, etc.), and (5), avoidance of unnecessary procedures and radiation exposure.

    Since hypercalcemia and hyperparathyroidism are common, the result of this study has significantly helped our clinicians (primary care physicians, internists, endocrinologists, nuclear medicine specialists, radiologists, ear, nose, and throat surgeons, and endocrine surgeons) improve care for their patients.

     To use the parathyroid scan calculator, clinicians can enter the serum ionized calcium, serum phosphate, and serum intact PTH levels and then press “calculate” in order to get the probability result. The calculator uses the following formula to calculate the probability, based on the regression from the paper by Hoang et al (2):

The logistic probability model used

π (x) =

e-0.313+ (β1χ1) +  (β2χ2) +  (β3χ3)
z + e-0.313 + (β1χ1) +  (β2χ2) +  (β3χ3)

The estimated parameters of the model are: β1 = 0.455,β2 = 0.756 and β3 = 1.727. 

The following limits were added: if the serum phosphate level is >3.0 mg/dL (χ1 = 1), if the serum intact parathyroid level is <90 pg/mL (χ2 = 1), and when the serum ionized calcium is <6.0 mg/dL (χ3 = 1).  Note:  the cutoff value for ionized calcium is adjustable (see below).  Note: z =1 unless any of the inputs hit the cutoff value and then z =10.

Phosphate level (mg/dL)    

Parathyroid intact level(pg/mL)   Cutoff level:

Ionized calcium level(mg/dL)
   Cutoff level:


.       .


  1. Lumachi F, Zucchetta P, Angelini F, et al. Tumors of the parathyroid glands. Changes in clinical features and in noninvasive localization studies sensitivity. J Exp Clin Cancer Res. 2000;19:7-11.

  2. Hoang TD, Jani AG, Mai VQ, Tuamokumo FO, Shakir MKM. Associations of serum ionized calcium, phosphate, and PTH levels with parathyroid scan in primary hyperparathyroidism. Endocr Pract. 2019:25:16-22.

  3. Endocrinology diabetes, and metabolism questionnaire. Available at: ParathyroidScanScoreCalc.aspx. Accessed March 1, 2020.

Parathyroid Scan Score Calculator