Rapid Assessment of Coagulation at the Point of Care With the Hemochron Signature Elite System

Abstract

Real-time point-of-care (POC) measurement of coagulation parameters, including activated clotting time (ACT), activated partial thromboplastin time, and prothrombin time with calculated international normalized ratio can improve patient outcomes in clinical settings, such as surgical and minimally invasive cardiac procedures, critical care units, and emergency departments. Point-of-care analyzers used in these settings must be small, portable, robust, and easy to use. The Hemochron Signature Elite system (Instrumentation Laboratory) offers 6 types of single-use disposable coagulation test cartridges, ACT+ (to measure high to moderate unfractionated heparin concentrations), ACT-LR (to measure moderate to low unfractionated heparin concentrations), activated partial thromboplastin time (citrate or whole-blood samples), and prothrombin time/international normalized ratio (citrate or whole-blood samples). Using a mechanical clot-detection technology, 1 to 2 drops of blood are mixed with an assay-specific reagent. Results are analyzed, displayed, and archived within minutes of testing. An integral barcode reader scans patient and operator IDs, and reagent lot details for documentation and traceability. The system supports remote connectivity (POCT01-A–compliant) and POC management of data, operators, and analyzers with GEMweb Plus 500 Custom Connectivity solution (Instrumentation Laboratory). The Hemochron Signature Elite system provides rapid and reliable testing with the broadest coagulation test menu of any POC instrument.

In many acute care settings (eg, emergency department and intensive care units), rapid assessment of coagulation using a point-of-care (POC) system to monitor the response of anticoagulation administration can improve care and outcomes.¹ Moreover, in critical procedures, such as cardiopulmonary bypass (CPB), cardiac catheterization, and neurointervention,² unfractionated heparin (UFH) is the most commonly used anticoagulant.³ Complicating the administration of UFH is the variability in anticoagulant response that can be observed between individuals undergoing the same procedure.⁴ Dosing protocols established on a weight-based algorithm alone often requires additional adjustments to compensate for the patient's drug response. This variability in individual response can result in overdosing or underdosing of UFH with potentially serious clinical consequences (bleeding or thrombosis, respectively).^5–7 Therefore, it is important to assess coagulation before, during, and after these procedures.⁸ In addition, POC coagulation testing is also valuable in monitoring vitamin K antagonist (VKA) therapy in oral anticoagulation clinics.⁹

GOALS AND OBJECTIVES OF POC COAGULATION INSTRUMENTS

Point-of-care coagulation tests include activated clotting time (ACT), prothrombin time/international normalized ratio (PT/INR), and activated partial thromboplastin time (APTT).^10–15 The results from these assays can be integrated into clinical protocols and limit the potentially prolonged turnaround times when analysis is conducted in the central laboratory. To successfully accomplish this goal, the POC instrument must provide rapid, actionable results and be adaptable to the unique environments posed in acute care settings. It must be small, portable, easy to use, and designed to minimize the risks of errors, and it should include functions that enhance safety and laboratory regulatory and accreditation standards, as well as support connectivity and data management.¹⁶

Point-of-care analyzers should be developed with the objective of simplicity in operation, and it is essential that the instrument be efficiently operated by a variety of health care providers. These characteristics allow practitioners to focus on addressing the immediate demands of patient management using timely test results rather than diverting their attention on performing intricate, time-consuming operational procedures that may require high laboratory skill levels to execute.

HEMOCHRON SIGNATURE ELITE

The Hemochron Signature Elite system (Instrumentation Laboratory, Bedford, Massachusetts; Fig. 1) meets all the goals and objectives of a POC coagulation instrument and is built on a legacy of accurate and reliable testing technology. Starting with the Hemochronometer, the first ACT instrument to be commercially released in 1969, through 11 subsequent generations, Hemochron design innovations have provided the broadest coagulation test menu of any POC instrument.

FIGURE 1: Hemochron Signature Elite system.

The Hemochron Signature Elite system uses a single analytical platform and 6 types of single-use disposable coagulation test cartridges (Table 1):

TABLE 1 - Hemochron Signature Elite Assays^10–15

Assay Name	Reportable Range	Test Specifications	Reagent
ACT+	65–1005 s*	UFH sensitivity: 1–6 IU/mL Unaffected by aprotinin	Kaolin, silica, phospholipids
ACT-LR	68–400 s*	UFH sensitivity: up to 2.5 IU/mL	Celite, silica, potato dextrin
APTT	20–400 s†	UFH sensitivity: up to 1.5 IU/mL	Kaolin, phospholipids
Citrated APTT	20–400 s†	UFH sensitivity: up to 1.5 IU/mL	Kaolin, phospholipids, calcium salts
PT	0.8–10.0 INR	ISI = 1	Thromboplastin
Citrated PT	0.8–10.0 INR	ISI = 1	Thromboplastin, calcium salts

*Celite equivalent seconds.

†Plasma equivalent seconds.

ISI indicates international sensitivity index.

• ACT+ (ACT testing for moderate-to-high UFH concentrations)
• ACT-LR (ACT testing for low-to-moderate UFH concentrations)
• APTT (citrate or fresh whole-blood samples for very low UFH concentrations)
• PT/INR (citrate or fresh whole-blood samples for performing a quantitative 1-stage PT and monitoring VKA therapy).

Blood conservation is another important attribute of the system; all 6 coagulation test types are performed with only 1 to 2 drops of blood, allowing for greater flexibility for numerous clinical applications and settings.

To perform a test with the Hemochron Signature Elite system, the operator simply inserts a cartridge, adds blood to the cartridge's sample well, and presses “START.” Results are available within minutes, are displayed and archived onboard the instrument, and can be printed or transmitted to the hospital or laboratory information system. After test completion, the operator removes and discards the cartridge.¹⁷

PRINCIPLE OF CLOT DETECTION

The Hemochron Signature Elite system assesses coagulation by mechanically detecting clot formation. The measurement begins when blood is placed in the sample well. A 15-μL aliquot is drawn into the measurement channel and mixed with the reagent in the cartridge (Fig. 2). Each test type contains a reagent specific to its associated assay (Table 1). The blood is then pumped back and forth through a restriction within the cartridge's measurement channel. The blood movement in the channel is monitored by optical detectors, and upon reaching a predetermined flow rate, the test ends, indicating the formation of a fibrin clot.^10–15,17

FIGURE 2: Hemochron Signature Elite cartridges.

This clot-detection methodology, which is centered on identifying a fibrin end point clot, ensures that the Hemochron Signature Elite system provides accurate and reliable results.

HEMOCHRON SIGNATURE ELITE FEATURES

To facilitate compliance and accreditation, an internal optical detector identifies the test type when a cartridge is inserted. The barcode reader is then used to scan the patient identification (ID), operator ID, and quality control (QC) lot details. This eliminates transcription errors and provides traceability and an audit trail. Patient testing is locked out if required QC testing has not been completed, QC fails, the cartridge has expired, or (optionally) for uncertified operators. By scanning operator IDs and locking out uncertified users, the Hemochron Signature Elite system supports compliance to POC testing regulatory/accreditation requirements for personnel training and competency certification, and ensures strict adherence to the testing procedures of each institution.¹⁷

Furthermore, the time between liquid QC measurements can be set by the user, every 8 to 24 hours, to accommodate specific needs of the facility. Two levels of liquid QC are required to validate the performance of each new cartridge lot and every 30 days thereafter. The system also incorporates an optional, automated 2-level electronic quality control capability, to act as a surrogate QC, reducing requirements for liquid QC.^10–15

Allowing for flexible configuration, each Hemochron Signature Elite system can be tailored for the uniqueness of a specific testing area, including the test cartridge types appropriate for the clinical applications provided, the operators assigned to that location, and the QC requirements deemed appropriate for that setting. Compliant to Clinical and Laboratory Standards Institute POCT01-A, data transmission to all major middleware providers through ethernet or serial communication options are enabled. In addition, GEMweb Plus 500 Custom Connectivity (Instrumentation Laboratory) captures patient and QC test results, tagged with patient and operator IDs, error codes, operator comments, and other data. Supported middleware systems are listed in Table 2.

TABLE 2 - Middleware Supported by the Hemochron Signature Elite System

System	Manufacturer/Distributor
GEMweb Plus Custom Connectivity	Instrumentation Laboratory
RALs	Abbott
TELCOR	TELCOR
POCcelerator	Siemens

ACT TESTS

Clinical Considerations for ACT Testing

All ACT tests activate the intrinsic coagulation pathway, accelerate fibrin formation, and produce a shorter clotting time versus nonmanipulated blood samples. However, the Hemochron Signature Elite system, including its maximally activated reagents for ACT+ and ACT-LR, produces significantly shorter clotting times than do other systems. If ACT results were reported in real-time seconds by the Hemochron Signature Elite system, they could not be interpreted using conventional protocols. Therefore, to better align with clinical expectations, the Hemochron Signature Elite system incorporates a validated algorithm that accelerates numeric counting during ACT testing. The reported results are more closely correlated with traditional decision-making values (target times), commonly used when monitoring the anticoagulation effects of UFH. This hallmark feature of Hemochron Signature Elite ACT+ and ACT-LR tests is known as “RapidCount Technology.”

The ACT+ and ACT-LR cartridges contain multiple activators to ensure maximal stimulation of the intrinsic pathway. Tests using a maximally activated reagent support current clinical practice guidelines, are less affected by hypothermia and artifacts, allow for shorter testing time, and diminish potential variability induced by hemodilution.¹⁸

Activated clotting time is distinctive among coagulation assays, as it exists exclusively at the POC and is not measured in the laboratory. There are no standardized, traceable, clot-activating reagents, and there is no laboratory “reference” analyzer to compare against. Each ACT test manufacturer uses different reagent activators and/or concentrations to activate in vitro. In addition, each manufacturer uses a different methodology to detect when end point clot formation is reached, and the hardware and software controlling the specimen temperature for each device are different. Some analyzers warm the specimen to 37°C within seconds, whereas others take minutes to reach the same temperature. The combination of these characteristics generates a unique analytical profile for each ACT system. Because of these variations, different instrument models will report different ACT values.

To effectively interpret ACT results and manage UFH administration, it is essential for each institution to perform a simple correlation study to evaluate how the results from a new ACT system compare with a system using different technology. In such correlation studies, the Hemochron Signature Elite system typically reports target ACT results by as much as 50% faster than competitive instruments with similar test results because of RapidCount Technology.

The Hemochron Signature Elite offers 2 ACT assays: ACT+ and ACT-LR. The ACT+ cartridge is intended for monitoring moderate-to-high UFH concentrations and is commonly used during CPB and cardiac ablation procedures. The ACT-LR assay is intended for monitoring low heparin concentrations, common in diagnostic and interventional cardiac catheterization, neurointerventional procedures, extracorporeal membrane oxygenation (ECMO), and transcatheter aortic valve replacement.

ACT+ Performance Characteristics

Precision and normal reference range for the Hemochron Signature Elite ACT+ test are summarized in Table 3.

TABLE 3 - Performance Evaluations for Hemochron Signature Elite ACT+ Cartridge¹⁰

Measurement*
Laboratory precision testing protocol	Normal level control, ACT+ mean ± SD (%CV)	Abnormal level control, ACT+ mean ± SD (%CV)
Overall (n = 36/3 d/3 instruments)	155.5 ± 9.8 (6.3)	397.1 ± 31.8 (8.0)
Day-to-day (n = 3/3 d/1 instrument)	156.9 ± 8.3 (5.3)	395.7 ± 27.7 (7.0)
Clinical precision testing protocol	Correlation coefficient
CPB and PCI patients, duplicate tests (n = 24)	r = 0.99
Normal reference range	ACT+ range, mean ± 2 SD
Healthy volunteers (n = 20)	81–125
Hospitalized patients not receiving UFH (n = 100)	96–152

*ACT+ values reported in Celite equivalent seconds.

CV indicates coefficient of variation.

Analysis of post-heparin bolus clotting times during percutaneous transluminal cardiac angioplasty and cardiac surgery, requiring CPB, indicates that ACT+ may yield target ranges approximately 10% to 15% shorter than corresponding Celite ACT values. This represents approximately 260 to 270 ACT+ seconds at a 300-second Celite ACT in percutaneous transluminal cardiac angioplasty and approximately 410 to 440 seconds at a 480-second Celite ACT in cardiac surgery, before initiation of CPB.¹⁰

ACT-LR Performance Characteristics

Precision and normal reference range for the Hemochron Signature Elite ACT-LR test are summarized in Table 4.

TABLE 4 - Performance Evaluations for Hemochron Signature Elite ACT-LR Cartridge¹¹

Measurement*
Laboratory precision testing protocol	Normal level control, ACT-LR mean ± SD (%CV)	Abnormal level control, ACT-LR mean ± SD (%CV)
Overall (n = 27/3 d/3 instruments)	208 ± 14 (6.7)	299 ± 11 (3.8)
Day-to-day (n = 3/3 d/1 instrument)	211 ± 13.4 (6.4)	298 ± 10.8 (3.6)
Clinical Precision testing protocol	Correlation coefficient
Cardiovascular patients with ACT-LR results 87–400 s (n = 76)	r = 0.93
Normal reference range	ACT-LR range, mean ± 2 SD
Healthy volunteers (n = 21)	113–149
Cardiac catheterization and ECMO patients, not receiving UFH (n = 20)	89–169

*ACT-LR results reported in Celite equivalent seconds.

In an evaluation of 20 patients at the completion of percutaneous coronary intervention (PCI) or at 5 to 24 hours after heparin bolus when the indwelling vascular sheath was removed, the ACT Celite test reported a mean of 142 seconds (68–216 seconds) and the correlated ACT-LR reported a mean of 145 seconds (83–207 seconds).¹¹

APTT TESTS

The APTT assay activates the intrinsic pathway and is used to monitor very low concentrations of UFH. Two APTT cartridges are offered: APTT for immediate testing with fresh whole blood and a citrated APTT for delayed testing.^12,13 Test results for the APTT cartridges are reported within 2 minutes for the fresh, noncitrated test and 7 minutes (including a 5-minute incubation time for the citrated tube) for the citrated APTT test.

Fresh Whole-Blood APTT Performance Characteristics

Precision and normal reference range for the Hemochron APTT test in fresh whole blood are summarized in Table 5.

TABLE 5 - Performance Evaluations for Hemochron Signature Elite Fresh Whole-Blood APTT Cartridge¹²

Measurement
Laboratory precision testing protocol	Normal level control, APTT mean ± SD (%CV), WBS	Abnormal level control, APTT mean ± SD (%CV), WBS
Overall (n = 18/2 lots/3 d)	99.8 ± 2.3 (2.3)	204.5 ± 9.0 (4.4)
Normal reference range	APTT range, mean ± 2 SD, PES
Healthy volunteers (n = 30)	23.2–38.7

WBS, whole blood seconds.

In clinical studies, fresh blood samples (n = 48) were collected from preprocedure and postprocedure PCI patients and were tested with the APTT cartridge. An aliquot from each specimen was mixed with citrate and centrifuged. The specimens were sent to the laboratory for plasma APTT analysis. The APTT whole-blood results on the Hemochron Signature Elite system were converted to plasma equivalent seconds (PES) and compared with the laboratory result, yielding a correlation coefficient of r = 0.92.¹²

Citrated Whole-Blood APTT Performance Characteristics

Precision and normal reference range for the Hemochron Signature Elite APTT test in citrated whole blood are summarized in Table 6.

TABLE 6 - Performance Evaluations for Hemochron Signature Elite Citrate APTT Cartridge¹³

Measurement
Laboratory precision testing protocol	Normal level control, citrated APTT mean ± SD (%CV), WBS	Abnormal level control, citrated APTT mean ± SD (%CV), WBS
Overall (n = 18/2 lots/3 d)	93 ± 5.85 (6.25)	200.5 ± 8.2 (4.1)
Normal reference range	Citrated APTT range, mean ± 2 SD, PES
Healthy volunteers mixed with 3.2% citrate (n = 36)	20.6–38.6

In clinical trials, a method correlation study was performed using fresh citrated whole-blood samples obtained from 210 pre- and post-PCI patients and tested with a citrated APTT cartridge. An aliquot of each specimen was mixed with citrate and centrifuged. The specimens were sent to the laboratory for PTT analysis. The citrated APTT results on the Hemochron Signature Elite system were converted to PES and compared with the laboratory result, yielding a correlation coefficient of r = 0.88.¹³

PT/INR TESTS

In contrast to APTT, the PT assay activates the extrinsic pathway and, like the APTT cartridges, is available for both fresh and citrated whole-blood specimens. The PT/INR assay can be used in a wide variety of clinical applications, such as monitoring VKA therapy, evaluating the coagulation status before and after blood transfusions, and assessing patients with traumatic coagulopathy.^14,15,19 Test results for the PT cartridges are reported within 2 minutes for the fresh, noncitrated test and 7 minutes for the citrated test.

Fresh Whole-Blood PT/INR Performance Characteristics

Precision and normal reference range for the fresh PT test are summarized in Table 7.

TABLE 7 - Performance Evaluations for Hemochron Signature Elite Fresh Whole-Blood PT Cartridge¹⁴

Measurement
Laboratory precision testing protocol	Normal level control, INR mean ± SD	Abnormal level control, INR mean ± SD
Overall (n = 45/3 d/3 instruments)	2.3 ± 0.7	8.9 ± 0.43
Day-to-day (n = 15/3 d/1 instrument)	2.3 ± 0.28	9.1 ± 0.34
Normal reference range	INR range, INR mean ± 2 SD
Healthy volunteers (n = 36)	0.8–1.4

In clinical studies, PT was assessed in 3 hospital-based oral anticoagulation outpatient clinics on fresh, whole-blood samples obtained by venipuncture from 108 routinely monitored patients. Each hospital had a unique instrument-reagent combination. A portion of each whole-blood sample was tested on the Hemochron PT test, and the remainder was mixed with sodium citrate and sent to the laboratory for analysis. All tests were performed in duplicate and compared with the laboratory result, yielding a correlation coefficient of r = 0.91.¹⁴

In a separate analysis, the influence of the blood collection method was evaluated in 50 patients. Fresh whole-blood PT tests, using blood obtained from finger sticks (capillary specimens), were compared with those collected by venipuncture, resulting in a correlation coefficient of r = 0.95. The finger-stick results were also correlated with the laboratory plasma results, yielding a correlation coefficient of r = 0.88.¹⁴

Citrated Whole-Blood PT/INR Performance Characteristics

Precision and normal reference range for the citrated PT test are summarized in Table 8.

TABLE 8 - Precision Evaluations of Hemochron Signature Elite Citrate PT Cartridge¹⁵

Measurement
Laboratory precision testing protocol*	Normal level control, citrated PT mean ± SD (%CV), WBS	Abnormal level control, citrated PT mean ± SD (%CV), WBS
Overall (n = 55/2 d)	26 ± 1.9 (7.4)	55 ± 2.7 (5.0)
Day-to-day (n = 12/4 d)	27 ± 1.7 (6.3)	56 ± 2.2 (2.2)
Operator (n = 45/3 operators)	26 ± 1.3 (5.0)	55 ± 2.2 (3.9)
Lot-to-lot (n = 15/3 cartridge lots)	25 ± 1.7 (1.7)	54 ± 2.3 (4.2)
Normal reference range	Citrated INR range, mean ± 2 SD
Healthy volunteers mixed with 3.2% citrate (n = 59)	0.8–1.5

*All precision testing conducted with up to 6 instruments.

In clinical studies, fresh, citrated whole-blood samples, obtained from 233 patients receiving VKA therapy, were tested with a citrated PT cartridge and validated at 4 clinical sites. The citrated PT results were compared with a second aliquot analyzed in the laboratory with a plasma-based assay. Results of the comparison yielded a correlation coefficient of r = 0.92.¹⁵

SUMMARY

The Hemochron Signature Elite system provides rapid and reliable testing with the broadest coagulation test menu of any POC instrument. Fibrin clot detection and RapidCount technology ensure quality control and safe instrument operation. The system has proven utility in a wide variety of clinical applications and acute care settings.