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Degree Of Parathyroid Hormone Elevation In Primary Hyperparathyroidism: Does Time Of Day Matter?
*C. Corbin Frye, *Janessa Sullivan, *Jingxia Liu, *Taylor Brown, *William Gillanders, T.K. Pandian
Washington University, St. Louis, MO

OBJECTIVE(S): Parathyroid hormone (PTH) levels have been shown to have a predictable circadian rhythm in patients with normal parathyroid function, but this has not been described in patients with primary hyperparathyroidism (PHPT). Anecdotally, we observed that PTH levels obtained early on the morning of surgery seemed to be lower than other values obtained prior to the day of surgery. If true, this has the potential to impact the interpretation of intra-operative PTH levels. We hypothesized that early morning PTH values would be significantly lower than PTH values obtained later in the day in patients with PHPT.
METHODS: We performed an IRB-approved, retrospective chart review of patients undergoing parathyroidectomy for PHPT between October 2019 and October 2021. Only patients who had a day-of-surgery, pre-incision PTH level were included. Patient, operative, and laboratory parameters were collected. The three most recent PTH values in addition to the day-of-surgery, pre-incision PTH values were studied. Analysis was performed using mixed models for repeated measures with a first-order autoregression correlation structure. PTH values were compared before and after hourly intervals between 6am and 12pm. Significance was considered when p<0.05.
RESULTS: Among 93 patients, mean age at time of surgery was 60.1 years and 84% were female. A focused, unilateral exploration was performed in 59% and single-gland disease was identified in 65% of patients. Only 2 patients in this cohort had persistent or recurrent disease. The median PTH level before the day of surgery was 113 pg/mL and the median day-of-surgery, pre-incision PTH level was 99 pg/mL. PTH values collected before 6am were found to be significantly lower than PTH values collected after 6am (p<0.05). Statistically significant differences in PTH levels were not noted at other morning time cut-offs, although a trend toward lower PTH levels collected before 8am was observed (p=0.07).
CONCLUSIONS: Consistent with the circadian variability of PTH found in normal parathyroid function, our data suggest that patients with PHPT may have an early morning reduction in PTH elevation. As such, surgeons may wish to consider specimen collection time when using pre-incision PTH levels as a baseline for intra-operative PTH level interpretation.


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