Validation and implementation of an intraoperative parathyroid hormone assay and workflow: practical advice for endocrine surgery centres

Introduction

In the United States, primary hyperparathyroidism (PHPT) has an age-adjusted prevalence of 233 per 100,000 women and 85 per 100,000 men [1]. It is associated with osteoporosis, nephrolithiasis, fatigue, constipation, and/or neurocognitive changes [2]. Surgical extirpation of hyperfunctioning parathyroid tissue is required to achieve cure in PHPT. Over 30 years ago, Irvin and colleagues developed intraoperative parathyroid hormone (IOPTH) monitoring, which harnesses the short half-life of parathyroid hormone (PTH) to guide surgeons during parathyroid gland resection [3]. These assays have been adopted by a number of endocrine surgery centres internationally, but challenges remain in terms of optimizing IOPTH sample processing and turnaround time (TAT) and promoting institutional adoption [4]. In 2016, the American Association of Endocrine Surgeons recommended IOPTH monitoring to improve surgical success when performing minimally invasive parathyroidectomy for localized PHPT [5]. Commercially available PTH immunoassays that target “intact” PTH (amino acids 1–84) have shown improvements in their TAT with modern assays demonstrating an analytical time of 10–20 min, but this does not account for time delays secondary to sample transport and result reporting [6]. Central laboratory-based IOPTH assays have also been shown to be more cost-effective when compared to point-of-care IOPTH tests, but this remains somewhat controversial [6], [7], [8], [9]. Turnaround time in central laboratory-based IOPTH assays, however, can be prolonged due to the lack of on-site facilities, delays in processing and assay run-length, and/or a lack of dedicated laboratory staff [6]. As central laboratory-based IOPTH assays must account for added personnel, coordination between surgical and laboratory teams, and feasibility challenges, it is imperative that an efficient workflow exist to standardize IOPTH assay performance and therefore, broaden the worldwide adoption of this recommended intraoperative adjunct. The goals of this study were (1) to implement a central laboratory-based IOPTH monitoring assay; (2) to validate the analytical measuring range and introduce a novel dilutional protocol for analyzing IOPTH levels elevated beyond the upper analytical limit of the assay; (3) to describe an IOPTH workflow that can be adopted by other institutions.

Materials and methods

Results

Imprecision and analytical measuring range

The Elecsys^® IOPTH assay demonstrated linearity from 505 pmol/L to 0.8 pmol/L (Figure 1). Within-and between-day imprecision CV were ≤3 % for QC material with values from 2.45 pmol/L to 44.56 pmol/L. We were not able to validate the LOD (0.13 pmol/L) as the assay showed non-specific signals with water (1.51 pmol/L) and saline (1.29 pmol/L) when measured and thus we were unable to also calculate the limit of blank, which is needed to calculate the LOD. However, using pooled EDTA samples we obtained an imprecision of 6 and 3 % at concentrations of 0.54 and 0.71 pmol/L. A 1:1 dilution of the Maine standard (i.e., 505 pmol/L) with pooled patient samples with low PTH level (i.e., 0.38 pmol/L) yielded IOPTH of 250.8 pmol/L when corrected for dilution [i.e., (2 × 250.8)–0.38] yielded as result of 501 pmol/L (i.e., >99 % recovery from the established value of 505 pmol/L).

Figure 1:

Elecsys^® intraoperative parathyroid hormone assay linearity.

Instrument and method comparison

Passing–Bablok regression showed a slight proportional bias of approximately 5 % (i.e., near the observed imprecision of the assay) between the Cobas e411 instruments [SJHH Roche PTH=0.95 (95 % CI: 0.90, 0.99) × TGH Roche PTH − 0.05 (95 % CI: −0.20, 0.09)] (Figure 2). This was confirmed with difference plots (mean % bias=−5.2 %, 95 % CI: −7.8, −2.6) and Bland–Altman analyses demonstrating a mean difference of −5.5 % with 95 % limits of agreement being −17.6–6.5 % and a high correlation between instruments (r=0.998). The method comparison between Roche PTH and Ortho PTH was difficult to assess due to lower correlation (r=0.959) between these methods [SJHH Roche PTH=0.91 (95 % CI: 0.73–1.1) × SJHH Ortho PTH: + 0.1 (95 % CI: −0.34 to 0.76)] (Figure 3).

Figure 2:

Method comparison of intraoperative parathyroid hormone assays between two Roche Diagnostics Cobas^® e411 instruments. PTH, parathyroid hormone; SJHH, St. Joseph’s Hospital Hamilton; TGH, Toronto General Hospital.

Figure 3:

Method comparison of parathyroid hormone measured by Roche Cobas e411 at Ortho Vitros XT 7600 at our centre. PTH, parathyroid hormone.

Intraoperative parathyroid hormone assay workflow and case series

Before we implemented IOPTH at our centre, all parathyroid surgery was aided by use of intraoperative frozen tissue analysis (IFTA). An internal projection identified that transition to using IOPTH would minimize hospital costs and alleviate the pathology sample backlog compounded by the COVID-19 pandemic. We decided to place the Cobas^® e411 analyzer in the central laboratory at SJHH, which is located two floors above the operating room. At a casual walking velocity, it takes approximately 140 s to transport samples from the operating suite to the analyzer. We outline in Figure 4 the scheduling, transport, and processing steps required to facilitate open communication between teams and minimize TAT for IOPTH samples. At our centre, the central laboratory immediately reports IOPTH to the operating room via telephone but does not provide calculations of the IOPTH reduction. We report the IOPTH assay results and clinical outcomes for the first 10 consecutive parathyroid surgery patients (Table 2). All patients were diagnosed with PHPT and most underwent minimally invasive parathyroidectomy for a localized single parathyroid adenoma. Our centre uses the Miami IOPTH criteria to declare intraoperative cure and surgical case completion [11]. In this cohort, all patients were diagnosed with localized PHPT and did meet the Miami criteria at 10- or 15-min post-gland excision timepoints. Based on personal preference, surgeons used central or peripheral venous sampling for obtaining IOPTH samples, but this has not been shown to impact relative IOPTH kinetics [12]. The mean time from skin incision to closure (i.e., operating time) was 47.1 min (SD: 9.1 min). The TAT between IOPTH samples ranged from 9–31 min across all included patients with the longest time discrepancy occurring between the baseline and “at excision” IOPTH samples. The mean IOPTH TAT (i.e., from IOPTH sample draw to result reporting) between samples was 9.8 min (SD: 6.7 min). All patients with adequate data entry met criteria for cure at six months and final pathology for all patients was parathyroid adenoma. None of these patients required intraoperative frozen tissue analysis (IFTA) to guide parathyroid exploration. None of the presented patients required revision parathyroid surgery. In contrast, five consecutive parathyroid surgeries performed for localized PHPT prior to implementing our IOPTH program required a mean of 1.6 IFTA samples (range: 0–3 samples) and a mean time operating time of 67.4 min (SD: 19 min).

Figure 4:

Intraoperative parathyroid assay workflow at our centre. MLT, medical laboratory technologist; ORA, operating room attendant.

Table 2:

Intraoperative parathyroid hormone assay results for first consecutive ten patients.

Patient number	Sex	Age	Diagnosis	Imaging results	Preoperative corrected calcium, mmol/L	Type of surgery	IOPTH level, pmol/L						Operation time, minutes	Frozen section analysis	PTH at 6 months, pmol/L	Corrected calcium at 6 months, mmol/L	Clinical cure at 6 months	Final pathology
							Prior to surgery	Baseline	At gland excision	10 min after gland excision	15 min after gland excision	4 h after surgery
1	Male	67	PHPT	Single parathyroid adenoma	2.6	MIP	44	33	16.3	7.2	6	4.3	55	No	3.8	2.4	Yes	Parathyroid adenoma
2	Female	54	PHPT	Single parathyroid adenoma	2.7	MIP	16.6	21.0	4.4	2.0	2.1	0.5	49	No	2.2	2.4	Yes	Parathyroid adenoma
3	Male	74	PHPT	Single parathyroid adenoma	3.0	MIP	34.6	>>500 (initial); 774 (after dilution)	31.9	11.7	8.7	3.9	52	No	3.2	NA	Yes	Parathyroid adenoma
4	Female	75	PHPT	Single parathyroid adenoma	2.6	MIP	8.8	17.1	15.1	5.4	3.7	1.5	43	No	NA	NA	NA	Parathyroid adenoma
5	Female	65	PHPT	Single parathyroid adenoma	2.8	MIP	13.8	69.4	25.9	8.8	7.2	3.7	36	No	3.6	2.4	Yes	Parathyroid adenoma
6	Male	74	PHPT	Double parathyroid adenoma	2.9	BNE	25.8	19.4	20.8	7.4	6.5	NA	44	No	2.5	2.2	Yes	Parathyroid adenoma
7	Female	70	PHPT	Single parathyroid adenoma	2.7	MIP	8.9	19.1	9.7	3.9	2.9	1.3	63	No	3.6	2.4	Yes	Parathyroid adenoma
8	Female	71	PHPT	Single parathyroid adenoma	2.5	MIP	17.5	32.6	10.4	4.9	3.8	NA	40	No	3.9	2.5	Yes	Parathyroid adenoma
9	Male	46	PHPT	Single parathyroid adenoma	2.9	MIP	8.9	112.3	3.2	2.2	1.8	1.4	56	No	2.9	2.5	Yes	Parathyroid adenoma
10	Male	84	PHPT	Single parathyroid adenoma	2.8	MIP	11.6	22.4	20.1	5.4	3.7	3.3	33	No	4.8	2.2	Yes	Parathyroid adenoma

1. BNE, bilateral neck exploration; IOPTH, intraoperative parathyroid hormone; PHPT, primary hyperparathyroidism; MIP, minimally invasive parathyroidectomy; NA, not available.

Discussion

Herein, we describe the validation and implementation of an IOPTH assay and workflow protocol at a tertiary care endocrine centre in Canada. In the early 1990s, IOPTH assays were introduced to guide parathyroidectomy, and they have gained popularity amongst surgeons over the past 30 years [4], 13]. Quinn and colleagues demonstrated that IOPTH improves surgical cure and reduces revision surgery rates in patients undergoing focused parathyroidectomy for PHPT, while recent clinical guidelines recommended its use to guide surgery for PHPT [5], 14]. Our group is currently conducting a survey study to describe the adoption of IOPTH across North America [15]. We found via our validation studies that the third-generation Elecsys^® IOPTH analyzed via Cobas^® e411 performed like other commercially available IOPTH assays, was consistent with this same assay performed at other regional endocrine surgery centres, and we had a mean sample TAT <12 min. These findings are congruent with those of a large retrospective study over 10 years where the Roche Elecsys^® PTH assay achieved a median TAT of ≤25 min when evaluated on different analytical platforms and across different hospital testing locations [6], 16]. Our mean TAT is also consistent with studies demonstrating that central laboratory-based IOPTH assays perform similarly or better than point-of-care assays [17], 18]. The Roche Elecsys^® PTH assay analytical time of 9 min is important as other assays have significantly longer analytical time (i.e., 10–18 min for other commercial PTH assays) [6], 18], 19]. There are other variables, in addition to the analytical time, that can impact PTH interpretation; these include analyte stability, hemolysis, and/or other assay interferences (e.g., biotin), which can all contribute to discordant findings between assays, as demonstrated in our comparison of Elecsys^® and Vitros assays [20]. We also describe a dilutional protocol that may assist other medical laboratories when faced with PTH levels above the upper reference interval since such a protocol is not described in the Elecsys^® IOPTH assay IFU. Third-generation IOPTH assays, which detect full-length and post-translationally modified PTH, have higher specificity and can reflect treatment success faster than second-generation assays [21]. Third-generation assays have also been shown to perform better in normocalcaemic PHPT and parathyroid carcinoma, while improving assay performance in secondary and tertiary hyperparathyroidism [21], 22]. Central laboratory-based IOPTH assays have economic advantages and despite concerns for increased TAT, recent studies have shown no impact or possible reduction in operating times when compared to point-of-care assays [6], 7]. As such, we have successfully implemented a third-generation IOPTH assay to guide all parathyroid surgeries at our high-volume centre. Prior to October 2023, all parathyroid surgery was guided by IFTA, but due to the hospital costs and pathology backlog from the COVID-19 pandemic, we discontinued using IFTA and instead transitioned to IOPTH for all parathyroid surgeries. Intraoperative FTA is invasive, misleading when determining parathyroid functionality, pathologist-dependent, and costly when compared to IOPTH – hence, parathyroid surgeons are rethinking the role for IFTA in guiding parathyroid exploration [5], 23], 24]. Consistent with the literature, we also found that IFTA increased operating time by approximately 20 min and that IOPTH was associated with shorter operating time when compared to IFTA for guiding parathyroid exploration [24], [25], [26].

To help ensure that our IOPTH workflow performed optimally, it was developed in collaboration with head and neck surgeons, general surgeons, anesthesiologists, operating room personnel, laboratory medicine personnel, and hospital administrators. We performed modifications to our IOPTH workflow based upon the sample processing efficiencies proposed in a previous study [27]. So far, we have received positive qualitative feedback from hospital stakeholders and maintained operating room case turnover and efficiency as per operating room personnel; thus, we have summarized our IOPTH workflow and provided advice for other institutions planning on developing an IOPTH program (Table 3; Figure 4). We employed our electronic medical record system to facilitate IOPTH order communication, equipment gathering, and sample label generation prior to starting surgery, which is consistent with institutions showing that streamlining IOPTH requisitions and ensuring that all necessary equipment was contained in an assigned tote box improved IOPTH processing time [28]. Our embrace of open and constant communication between surgery and laboratory personnel ensures “closed loop” communication and helps to avoid any delays associated not having analyzer calibrated for surgery [27]. Other critical facets of our IOPTH workflow ensure that dedicated personnel are on standby to transport and analyze IOPTH samples, thus allowing us to avoid unforeseen transport delays associated with pneumatic tube systems. To further improve IOPTH efficiency in the future, we plan on implementing a method that allows laboratory personnel to directly access the surgical schedule; thus, avoiding communication lapses between surgical administrators and laboratory schedulers. As we increase our surgical case volume, we will continue to reflect and improve upon modifiable steps within our IOPTH workflow so that we can further streamline sample processing and resulting.

Conclusions

In conclusion, we described a validated and efficient central laboratory-based IOPTH workflow that streamlined turnaround time at our endocrine surgery centre. We instituted this collaborative IOPTH program due to the high costs and misleading results associated with IFTA, in addition to our pathology sample backlog compounded by the COVID-19 pandemic. We also provided practical advice and a dilutional protocol for hospitals looking to implement an IOPTH program and thus, advance evidence-based parathyroid surgery around the world.