Intraoperative vs Central Laboratory PTH Testing During

CLINICAL CHEMISTRY Frank H. Wians, Jr, PhD, MT(ASCP), DABCC, FACB Jody A. Balko, MMSc, MT(ASCP)SC Rebecca M. Hsu, MD William Byrd, PhD, HCLD William H. Snyder III, MD

Intraoperative vs Central Laboratory PTH Testing During Parathyroidectomy Surgery ABSTRACT Intact parathyroid hormone (PTH) testing can be performed rapidly, directly in the operating room, using the QuiCK-Pak System (Nichols Institute Diagnostics, San Juan Capistrano, CA) or in a central laboratory using the IMMULITE Immunoassay System and Turbo PTH assay (Diagnostic Products, Los Angeles, CA). Correlation between parathyroid hormone values obtained on EDTA plasma samples using these systems was good (r = 0.84); at 20-minutes after excision of a suspected hyperfunctioning parathyroid gland, diagnostic agreement between the two systems was 100%. Based on 50 parathyroid gland surgeries for each of a 3-year contract period, the cost of intraoperative vs central laboratory PTH testing per surgery was $760 and $360, respectively. Intraoperative parathyroid hormone testing using the QuiCK-Pak System provides faster, more reliable turnaround time for intraoperative PTH results and has other advantages over central laboratory PTH testing during parathyroid gland surgery. From the Departments of Pathology (Drs Wians and Hsu and Ms Balko), Obstetrics and Gynecology (Dr Byrd), and Surgery (Dr Snyder), The University of Texas Southwestern Medical Center, Dallas. Address correspondence to Dr Wians, The University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 752359073

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Glossary

CLS—Chemiluminometer System ICMA—Immunochemiluminometric assay ioPTH—Intraoperative parathyroid hormone IRMA—Immunoradiometric assay LI—Left inferior LS—Left superior MGD—Multiglandular disease OR—Operating room PE—Postexcision PTG—Parathyroid gland PTH—Parathyroid hormone RS—Right superior TAT—Turnaround time UGD—Uniglandular disease

L A B O R ATO RY M E D I C I N E

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Background

Nussbaum et al1 were the first to describe the central laboratory use of a rapid assay for the measurement of intact parathyroid hormone (PTH) levels in patients undergoing unilateral or bilateral neck exploration because of clinically suspected and biochemically documented primary hyperparathyroidism. Subsequently, Irvin and Deriso2 and Irvin et al3-5 improved further the application of rapid intact PTH measurement by taking advantage of an immunochemiluminometric assay for the quantitative measurement of intact PTH concentration in plasma samples and a portable cart with a microcentrifuge, kinetic enhancer module, automated tube washer, and a single-well chemiluminometer. By using this system, these authors were able to perform rapid PTH measurements using blood samples both obtained and assayed intraoperatively (ie, directly in the surgical suite) on patients undergoing parathyroid gland (PTG) surgery on an outpatient basis. Recently, Wians6 coined the term “point-ofsurgery testing” for this type of testing. Recently, Wenk et al7 reported their experience with central laboratory testing for intact PTH concentration using blood samples obtained intraoperatively and tested with the IMMULITE Turbo Intact PTH instrument/method (Diagnostic Products, Los Angeles, CA). We describe here our experience with PTH testing using blood samples obtained and tested intraoperatively using the self-contained cart (QuiCK-Pak System, Nichols Institute Diagnostics, San Juan Capistrano, CA) for quantifying intact PTH concentration using single-surgery QuiCK-Intraoperative PTH kits vs central laboratory Turbo PTH testing using the IMMULITE System.

Materials and Methods

3 100, where

[PTH]baseline

[PTH]timed represents the PTH concentration obtained at any of the aforementioned time intervals and [PTH]baseline is the preoperative or postPTG manipulation PTH concentration, whichever was highest. The criterion used for assessing complete excision of all hyperfunctioning PTGs was a reduction in PTH of more than 50%. We recorded the time of neck incision, removal of the first suspected hyperfunctioning PTG, and availability of the PTH result from the plasma sample obtained at 20 minutes after excision of the PTG. Lastly, using data from the patients’ hospital bills, we determined the total cost of an outpatient PTG surgery at our institution based on

Fig 2. IMMULITE Immunoassay System (Diagnostic Products, Los Angeles, CA) in the central laboratory of Dr William Byrd used to test parathyroid hormone concentrations of specimens obtained intraoperatively from one of the patients enrolled in this study.

the average cost of anesthesia, operating room, and recovery room time; the fixed costs of performing neck sonography, sestamibi scintigraphy, and tissue frozen section; and the cost of central laboratory or intraoperative PTH testing for only those patients (n = 7) in our study who underwent PTG surgery because of primary hyperparathyroidism. The cost of PTH testing was based on a 3year contract with purchase of a new QuiCK-Pak System ($30,000) or a refurbished IMMULITE System ($27,000), including a service agreement at no additional cost, in year 1 of the contract; 50

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Scientific Communications

[PTH]timed – [PTH]baseline

4

% Change in [PTH] =

Fig 1. QuiCK-Pak System (Nichols Institute Diagnostics, San Juan Capistrano, CA) in a surgical suite at Zale Lipshy University Hospital, Dallas, TX, during parathyroid hormone testing of EDTA plasma samples obtained intraoperatively from one of the patients enrolled in this study.

Section

By using the QuiCK-Pak and IMMULITE Systems, we quantified PTH concentration in EDTA plasma samples obtained intraoperatively from 10 consecutive patients undergoing PTG surgery, regardless of reason, at the Zale Lipshy University Hospital (ZLUH), Dallas, TX. Blood was collected from a peripheral vein into EDTA collection tubes preoperatively, after manipulation of the PTG(s), and at 5, 10, 20, and/or 30 minutes after removal of a suspected hyperfunctioning PTG in all patients. QuiCK-Intraoperative PTH testing was performed directly in the surgical suite using the QuiCK-Pak System operated by an experienced and fully trained medical technologist (J.A.B.; Fig 1) or chemical pathology fellow (R.M.H.), while Turbo PTH testing was performed by a technologist in a central laboratory (W.B.’s laboratory) using the IMMULITE automated immunoassay system (Fig 2). For IMMULITE testing, an aliquot of the same plasma samples tested intraoperatively using the QuiCK-Pak System was kept on wet ice and delivered promptly by courier to the central laboratory where it was tested for PTH concentration. Intact PTH testing was performed according to each manufacturer’s instructions using QuiCKIntraoperative PTH kits and the QuiCK-Pak System provided by Nichols Institute Diagnostics and Turbo PTH kits purchased from Diagnostic Products and the IMMULITE System in Dr Byrd’s laboratory. The performance characteristics of each method are shown in Table 1. We calculated the percentage change in PTH concentration over baseline using the formula:

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Table 1. Comparative Characteristics of the QuiCK-Pak and Turbo Intact PTH Methods* Method/Instrument Characteristic

QuiCK-Pak

Turbo

Instrument

Chemiluminometer

IMMULITE

Type of immunoassay

ICMA

ICMA

Solid phase

Polystyrene bead

Polystyrene bead

Capture antibody†

Goat polyclonal (39-84)

Goat polyclonal (44-84)

Signal antibody†

AE-conjugated goat polyclonal (1-34)

ALP-conjugated goat polyclonal (1-34)

Trigger/substrate solution

Hydrogen peroxide and sodium hydroxide

Lumigen

Type of specimen recommended for testing

EDTA plasma

EDTA plasma/serum

Centrifuge time, plasma/serum

1 min at 6,400 rpm/NA

1 min at 6,400 rpm/5-min at 3,000 rpm

Volume of specimen tested

0.2 mL

0.1 mL

Number of standards (concentration range)

6 (0-1,250 pg/mL [0-131.6 pmol/L])

2 (0-2,500 pg/mL [0-263.2 pmol/L])

Number of controls

2

2

Total incubation time 37°C

7 min at 400 rpm and 45°C and temperature

10 min with intermittent agitation at

3

1 continuous

2s

24 s

Number of wash cycles Counting time Time to first result

9 min

15 min

Analytic sensitivity

6 pg/mL (0.6 pmol/L)

4 pg/mL (0.42 pmol/L)

AE, acridinium ester; ALP, alkaline phosphatase; ICMA, immunochemiluminometric assay; NA, not applicable; PTH, parathyroid hormone. *Based on information contained in each manufacturer’s product insert. QuiCK-Pak System (Nichols Institute Diagnostics, San Juan Capistrano, CA), IMMULITE, Diagnostic Products, Los Angeles, CA; Lumigen [4-methoxy-4-(3-phosphatephenyl)-spiro-(1,2-dioxetane3,2’-adamantane)], LUMIGEN, Southfield, MI. † Numbers in parentheses refer to the amino acid portion of the intact, 84 amino acid–containing PTH molecule recognized by the antibody specified.

PTG surgeries per year, or 150 in 3 years; the cost of all primary and ancillary reagents over a 3-year period (QuiCK-Pak System and single-surgery PTH kits [maximum of 9 tests/kit], $76,364; IMMULITE System, 50 test kits and consumable reagents, $20,336); and labor costs assuming 2.5 hours of technologist time per PTG surgery at $20.74/h, including the cost of benefits (ie, 22% add-on to hourly wage of $17). Results

The PTH values obtained on samples collected at various time intervals during surgical exploration and removal of a suspected hyperfunctioning PTG(s) are shown in Table 2 for both the QuiCK-Pak and Turbo PTH methods. The correlation between 36 of the 41 paired quantitative PTH values by both of these methods (QuiCK-Pak, Turbo) is shown in Figure 3. The preoperative values (1,006 pg/mL, 1,113 pg/mL [105.9 pmol/L, 117.2 pmol/L] for patient 5 were excluded because the next highest (QuiCK-Pak, Turbo) PTH paired values were (197 pg/mL, 302 pg/mL [20.7 pmol/L, 31.8 pmol/L]) and inclusion of patient 5’s paired values, with no values between these limits, would have artificially improved

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the correlation coefficient. In addition, 4 sets of paired (QuiCK-Pak, Turbo) PTH values were excluded because 1 or both of the values in these sets was less than the lower limit of detection of the QuiCK-Pak (6 pg/mL [0.6 pmol/L]) or Turbo (4 pg/mL [0.4 pmol/L]) PTH assays (Table 1). Because the interpretation of intraoperative PTH results is based on the percentage change in PTH concentration, it is more important to look at this parameter, rather than the absolute PTH concentration. Figure 4 compares the percentage change in PTH concentration at each time point, using both the QuiCK-Pak and Turbo PTH methods, for all of our patients. Generally, with the exception of patients 6, 9, and 10, the percentage decline in PTH concentration over baseline exceeded 50% at 5 or 10 minutes after excision of a suspected hyperfunctioning PTG. For patients 6, 9, and 10, the 5-minute postexcision specimen demonstrated a percentage decline of less than 50% using the QuiCK-Pak PTH method and greater than 50% using the Turbo PTH method. By 20 minutes after excision, however, the percentage decline in PTH concentration was greater than 50% for these 3 patients and in closer agreement by both rapid PTH methods (Fig 4). Possible explanations for these findings, especially in patient 6, include the presence of

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Table 2. Intraoperative QuiCK-Pak and Central Laboratory Turbo Intact PTH Results QuiCK-Pak

PTH (pg/mL)* Turbo Type of PTG Disease

Preoperative Post-PTG manipulation 5 min PE 10 min PE 20 min PE

137 116 50 44 32

334 320 44 37 27

UGD

2

Preoperative 5 min PE 10 min PE 20 min PE

197 71 53 40

302 89 54 35

UGD

3

Preoperative 10 min PE 20 min PE

41