Overview
Definition:
Intraoperative parathyroid hormone (PTH) monitoring is a technique used during parathyroidectomy and thyroidectomy to confirm the successful removal of hyperfunctioning parathyroid tissue or the preservation of normal parathyroid glands
It involves serial measurements of PTH levels in peripheral blood to assess the gland's functional status in real-time.
Epidemiology:
Hyperparathyroidism affects approximately 1-4% of the population, with primary hyperparathyroidism being the most common indication for parathyroidectomy
Intraoperative PTH monitoring is now considered the gold standard for confirming parathyroid gland excision in many centers globally, significantly reducing the rate of persistent or recurrent hyperparathyroidism.
Clinical Significance:
Accurate localization and removal of abnormal parathyroid glands are crucial for successful surgical outcomes in hyperparathyroidism
Intraoperative PTH monitoring helps surgeons differentiate between normal and hyperfunctioning glands, confirm complete excision of hyperfunctioning adenomas or hyperplasia, and identify potentially missed or ectopic glands, thereby minimizing complications like hypoparathyroidism and persistent hypercalcemia
This technique is vital for optimizing patient care and improving surgical success rates, making it a key area of study for DNB and NEET SS aspirants.
Indications
Primary Hyperparathyroidism:
When a single adenoma is identified by preoperative imaging, it allows for focused unilateral exploration and confirmation of removal
For multiglandular disease or when imaging is equivocal, it aids in ensuring all hyperfunctioning glands are addressed and remaining normal glands are preserved.
Ectopic Parathyroid Adenomas:
To confirm the removal of an adenoma located in unusual sites such as the mediastinum or thyroid.
Renal Osteodystrophy:
In patients with severe secondary or tertiary hyperparathyroidism undergoing total parathyroidectomy with or without autotransplantation.
Reoperative Parathyroidectomy:
When previous surgery has altered anatomy, making gland identification difficult
Intraoperative PTH monitoring is invaluable in these complex scenarios.
Thyroidectomy:
To assess the viability and function of remaining parathyroid glands after thyroid resection, especially in cases of extensive thyroid cancer or difficult dissections.
Protocol Steps
Baseline Pth Level:
A baseline PTH level is drawn from peripheral venous blood immediately before making the incision
This serves as a reference point for subsequent measurements.
During Excision:
Once a suspect parathyroid gland is identified and removed, a PTH level is drawn from peripheral venous blood
For a successful parathyroidectomy (especially in single adenoma cases), a significant drop in PTH levels is expected
Typically, a >50% drop from baseline, or a PTH level < 50 pg/mL (depending on assay sensitivity and baseline), within 10-20 minutes of gland removal indicates success.
Subsequent Measurements:
If the initial drop is insufficient, or if multiple glands are suspected, additional PTH levels are drawn after removing other suspect glands
A second measurement is usually taken 15-20 minutes after the first specimen removal
Some protocols involve drawing blood from the venous effluent of the suspected gland (venous sampling) if a precise localization is needed, though this is less common now with routine peripheral sampling.
Confirmation Of Normocalcemia:
The ultimate goal is to achieve and maintain normocalcemia postoperatively
The PTH drop is a surrogate marker for adequate parathyroid tissue removal.
Final Pth Level:
A final PTH level is drawn before closing the surgical site to ensure sustained suppression, though this is often less critical than the initial post-excision drop if the initial criteria are met.
Interpretation And Criteria
Goldman Criteria:
A >50% decrease from baseline PTH and a PTH level < 50 pg/mL at 10-20 minutes post-excision is considered a successful outcome for focused parathyroidectomy in cases of single adenoma.
Rocha Criteria:
A drop of >50% from baseline within 10-20 minutes is a common indicator of successful removal of hyperfunctioning tissue.
Assay Variations:
Different PTH assays have varying normal ranges and sensitivities
It is crucial to be aware of the specific assay's characteristics and follow established laboratory guidelines.
Persistent Hypercalcemia:
Failure to meet the criteria, indicated by a persistent high PTH level or a minimal drop, suggests residual hyperfunctioning parathyroid tissue, necessitating further exploration or removal of additional glands.
Hypoparathyroidism:
An excessively rapid or profound drop in PTH may indicate removal of all parathyroid tissue, raising concern for postoperative hypoparathyroidism
Close monitoring of calcium levels is essential.
Technical Considerations
Timing Of Blood Draws:
Accurate timing of blood draws is critical
Samples should be drawn rapidly from a peripheral vein after gland removal and sent immediately to the lab for rapid PTH assay.
Blood Tubes:
Use appropriate EDTA tubes for PTH measurement
Avoid hemolysis, as it can interfere with assay results.
Laboratory Turnaround Time:
Establish a reliable and rapid turnaround time with the laboratory for PTH assays, ideally within 10-15 minutes of sample receipt.
Number Of Glands Removed:
The interpretation differs for single gland adenoma versus multiglandular disease
In multiglandular disease, the target is often near-complete suppression of all hyperfunctioning glands, not necessarily a specific absolute PTH value.
Echocardiographic Confirmation:
In some cases, especially with ectopic glands, intraoperative ultrasound can be used to locate the removed gland, and venous sampling from the surrounding vessels can be performed for PTH analysis.
Complications
Persistent Hyperparathyroidism:
Failure to achieve adequate PTH suppression indicates residual hyperfunctioning parathyroid tissue, leading to continued hypercalcemia
This may require reoperation.
Postoperative Hypoparathyroidism:
Excessive removal of parathyroid tissue, or devascularization of remaining glands, can lead to symptomatic hypocalcemia
This is a serious complication requiring prompt calcium and vitamin D supplementation, and potentially hospitalization.
Recurrent Laryngeal Nerve Injury:
While not directly related to PTH monitoring, the surgical dissection required for gland identification and removal carries the risk of recurrent laryngeal nerve injury, leading to vocal cord dysfunction.
Bleeding And Hematoma:
Standard surgical risks including bleeding, hematoma formation, and infection are always present.
Damage To Adjacent Structures:
Risk of injury to the esophagus, trachea, or major vessels during extensive dissection, particularly in reoperative cases.
Key Points
Exam Focus:
Understand the typical PTH drop criteria (>50% from baseline, <50 pg/mL at 10-20 min) for focused parathyroidectomy
Know the role of PTH monitoring in reoperative surgery and multiglandular disease
Recognize the importance of rapid assay turnaround time.
Clinical Pearls:
Always draw baseline PTH before incision
Be familiar with your hospital's specific PTH assay and its reference ranges
A consistent drop is more important than an absolute value in complex cases
Intraoperative ultrasound can be a useful adjunct for localization and confirmation.
Common Mistakes:
Incorrect timing of blood draws, delayed transport of samples to the lab, misinterpretation of assay results due to assay variations, and failure to re-explore when PTH levels do not drop sufficiently
Forgetting to draw a baseline PTH is a critical error.