Parathyroid Scan Score Calculator (Revised 2020)
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):
probability model used
π (x) =
e-0.313+ (β1χ1) + (β2χ2) + (β3χ3)
z + e-0.313 + (β1χ1) + (β2χ2) +
The estimated parameters of the model are: β1 = 0.455,β2 = 0.756 and β3 =
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
Phosphate level (mg/dL)
Parathyroid intact level(pg/mL)
Ionized calcium level(mg/dL)
- 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.
- 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.
- Endocrinology diabetes, and metabolism questionnaire. Available at:
ParathyroidScanScoreCalc.aspx. Accessed March 1, 2020.