Whole Blood Platelet Aggregometry.

Light transmittance aggregometry is the historical reference method for platelet function testing and continues to be used extensively. Whole blood impedance lumiaggregometry represents an updated methodology that provides for simplified specimen management, an assay milieu that replicates in vivo platelet activation conditions, improved reproducibility, and near-patient testing. While the impedance-based whole blood aggregometer with luminescence channel is becoming the standard for platelet function testing using this methodology, at least three near-patient whole blood instruments are available, each employing its unique technology. We provide descriptions of whole blood lumiaggregometry and three near-patient systems. We include the principle of operation, materials, and stepwise example protocols and speculate on the importance of concordance among the platforms.

Measuring dabigatran with the dilute Russell viper venom confirm assay in an anticoagulation clinic population.

The dabigatran dose-response is predictable; however, it is necessary to measure plasma levels in a variety of clinical conditions. We evaluated a novel dabigatran measure - the 'dilute Russell viper venom confirm (DRVVC) assay' - against current developmental assays and a reference method. We measured plasma dabigatran and compared results from the Stago Sta-Clot DRVVC assay, Stago Ecarin Chromogenic Assay, Biophen Hemoclot Thrombin Inhibitor, and liquid chromatography tandem mass spectrometry. We obtained dabigatran calibrators and controls from Biophen, and performed the coagulation assays using a Stago STA-R Evolution coagulometer. Liquid chromatography tandem mass spectrometry method specimens were performed on an AB Sciex instrument at LabCorp. We enrolled 97 anticoagulation clinic patients (mean age 76 years) who were taking 150 mg dabigatran twice daily. All had creatinine clearances above 30 ml/min; patients were not excluded for concurrent medications or health issues. Citrated blood specimens were processed immediately, and stored at -70°C. We did not correlate collection time with medication time. We employed descriptive statistics, analysis of variance, and the Bland-Altman difference plot to assess the data. The range for all assays was 11.6-917 ng/ml. Analysis of variance generated a P value of 0.1 and Bland-Altman differences were all below 4.0% compared with DRVVC. The DRVVC measures dabigatran with validity comparable to other methods.

Comparison of six dilute russell viper venom time lupus anticoagulant screen/confirm assay kits.

BACKGROUND: The normalized dilute Russell viper venom time (DRVVT) ratio provides a robust assay methodology for lupus anticoagulant (LA) detection. OBJECTIVES: We evaluated six normalized DRVVT LA screen and confirm systems for inter-method consistency. Reagents were purchased from Diagnostica Stago, Inc. (Parsippany, NJ); Precision BioLogic Inc. (Halifax, Nova Scotia, Canada); Siemens Healthcare Inc. (Deerfield, IL); TCoag (Parsippany, NJ); Instrumentation Laboratories (Bedford, MA); and Sekisui Diagnostics (Pfungstadt, Germany). METHODS: For all assays, we employed the STA-R Evolution automated coagulometer, adhering to manufacturers' instructions. LA-positive and LA-negative plasma controls were purchased from Diagnostica Stago and pooled normal plasma (PNP) was purchased from Precision BioLogic. We computed the mean of the reference interval (MRI) and action limits for all kits using LA-negative aliquots from locally sourced normal subjects (n = 42). We then assayed locally sourced LA-positive plasmas (n = 43) and using analysis of variance compared uncorrected screen/confirm ratios and screen/confirm ratios that were normalized using MRI and mean PNP results. RESULTS: The grand mean action limit, MRI + 3 SD, derived from the local normal plasmas, was 1.2, confirming the manufacturers' recommended limits; however, limits must be locally computed. The all-sample p value was less than 0.001, indicating heterogeneity among ratios. When Sekisui ratios were excluded, the p value was 0.14, thus indicating that this method introduced the major difference among methods. Mean screen/confirm ratios computed from LA-positive specimens were 1.91 to 2.04 for reagent systems other than Sekisui, which instead yielded a mean ratio of 1.198, indicating that this method was relatively insensitive to LA. A negative bias was recorded by two lots from the Sekisui system for LA-positive specimens. Screen/confirm ratios from combined LA-positive and LA-negative samples generated a combined range of 1.59 to 1.67 for all reagents except Sekisui, which instead yielded 1.09. The within-run percent coefficient of variation (CV%) was less than 5.0% using all samples. Between-run CV% using Diagnostica Stago LA-positive and LA-negative controls was less than 5.5%. CONCLUSIONS: DRVVT screen/confirm ratios discriminate between LA-positive and LA-negative samples and generally provide acceptable reproducibility. Ratio results may vary among reagent-instrument combinations. In this study, normalization added little to the clinical result interpretation.

Career research opportunities for the medical laboratory scientist.

Medical Laboratory Scientists (MLS) typically practice in hospital laboratories; however there are multiple alternatives in research. This article details the advantages of working in a variety of research laboratory settings. These include public institutions, federal laboratory workplaces, private facilities, and industry settings. A view of the different research laboratory settings such as public institutions, federal laboratory workplaces, private facilities, and industry settings will be provided. An assessment on how MLS professionals can prepare for a career in research is outlined and the report concludes with a brief summary of the various aspects of the research setting.

Ability of the INNOVANCE PFA P2Y system to detect clopidogrel-induced ADP receptor blockade in preangiocath individuals.

We compared the ability of four test systems to detect platelet P2Y12 (ADP receptor) blockade by clopidogrel. The systems were the INNOVANCE PFA P2Y cartridge (PFA P2Y), the Accumetrics VerifyNow P2Y12 cartridge (VN P2Y12), whole blood aggregometry (WBA) using 5 (WBA 5) and 10 (WBA 10)  µmol/l ADP, and light transmittance aggregometry (LTA) using 20 (LTA 20)  µmol/l ADP. Blood was collected in 3.2% citrate from 101 preangiography participants who had received 300-600  mg of clopidogrel within 6-24  h or 75  mg daily for at least 7 days. Blood was also collected in 3.8% citrate for the PFA P2Y. Cut-offs indicating blockade were PFA P2Y, more than 106  s; VN P2Y12, less than 20%,  less than  235 Plavix resistance unit (PRU); WBA 5, less than 5  ohms; WBA 10, less than 8  ohms; and LTA 20, less than 50% aggregation. Percentage positives were PFA P2Y (3.2% citrate), 59%; PFA P2Y (3.8% citrate), 95%; VN P2Y12, 60%; VN P2Y12 PRU, 50%; WBA 5, 88%; WBA 10, 89%; and LTA 20, 72%. Percentage agreements were PFA P2Y 3.2% to VN P2Y12, 71%; PFA P2Y 3.2% to WBA 5 and 10, 64 and 65%, respectively; PFA P2Y 3.2% to LTA 20, 69%; PFA P2Y 3.8% to VN P2Y12, 71%, and to VN P2Y12 PRU, 60%; PFA P2Y 3.8% to WBA 5 and 10, 90% for both; PFA P2Y 3.8% to LTA 20, 76%; VN P2Y12 to WBA 5 and 10, 68 and 67%, respectively; and VN P2Y12 to LTA 20, 72%. PFA P2Y (3.2% citrate) detection compared favorably to VN P2Y12. The same system at 3.8% citrate compared more closely to WBA 5 and WBA 10.

Acinetobacter baumannii and MRSA contamination on reusable phlebotomy tourniquets.

OBJECTIVE: A study was undertaken to determine the incidence of Acinetobacter baumannii and methicillin resistant Staphylococcus aureus (MRSA) contamination on reusable phlebotomy tourniquets at Wilford Hall Medical Center, Lackland AFB, TX. DESIGN: Reusable tourniquets (n=200) were collected after being used for one day in the outpatient blood collection center (n=100) or during morning blood collection rounds on inpatient wards (n=100). Tourniquets were cultured and growth was screened for A. baumannii and S. aureus. A. baumannii isolates were identified using colonial morphology, oxidase, and GNI+ card on Vitek Legacy. S. aureus isolates were identified and screened for MRSA using colonial morphology, catalase, Staphaurex, and Oxacillin screening agar. RESULTS: Each outpatient tourniquet was used on an average of 33 patients and each inpatient tourniquet was used on an average of 11 patients. The overall contamination rate was 9% (18/200). A. baumannii was isolated from 11% (11/100) of the outpatient tourniquets and 3% (3/100) of the inpatient tourniquets. Methicillin-susceptible S. aureus was isolated from 2% (2/100) of the outpatient tourniquets and 3% (3/100) of the inpatient tourniquets. No MRSA was isolated. One ou'tpatient tourniquet had both A. baumannii and methicillin-susceptible S. aureus. CONCLUSIONS: Reusable tourniquets could serve as a potential reservoir for bacterial pathogens.

Effects of glucosamine and Celadrin on platelet function.

OBJECTIVE: The purpose of this study was to determine the effects of glucosamine and celadrin on platelet function. DESIGN: Baseline values were determined on the Chronolog 570VS platelet aggregometer with whole blood aggregation impedance readings using 2 different concentrations of ADP (5 microM, 10 microM), collagen (1 microg/mL), arachidonic acid (0.5 mM/L) and an Accumetrics whole blood platelet aggregation cartridge assay for P2Y12 receptors were obtained from 24 healthy volunteers. These subjects then took the suggested doses of Glucosamine with Celadrin (Stockbridge Naturals) as advertised (estimated 1500mg daily) for 2 weeks. Platelet aggregation analyses, as described above, were obtained after treatment. Statistics performed via a McNemar test. MAIN OUTCOME: Five of twenty-four subjects had at least a 20% difference in whole blood aggregation using the 5 microM concentration of ADP. A total of 6 and 7 subjects also showed a significant difference in platelet aggregation with administration of collagen and arachidonic acid, respectively. No significant differences were found with Accumetrics assay for P2Y12 in any of the subjects. CONCLUSION: Glucosamine and celadrin may inhibit platelet aggregation in some individuals via aspirin-like effects as well as inhibition of ADP receptor P2Y1 but not P2Y12.

Duration of Loxosceles reclusa venom detection by ELISA from swabs.

BACKGROUND: Diagnosis of Loxosceles reclusa envenomations is currently based upon clinical presentation. An enzyme-linked immunosorbent assay (ELISA) can detect surface Loxosceles venom at the envenomation site, allowing diagnostic confirmation. The length of time that venom on the skin is recoverable non-invasively is unknown. MATERIALS AND METHODS: To investigate duration of recoverable venom antigen, whole venom and fractionated sphingomyelinase D venom aliquots were injected subcutaneously in New Zealand White rabbits. Cotton and Dacron swabs were compared for venom recovery over a 21-day period using a surface swab technique. RESULTS: Significant amounts of Loxosceles reclusa antigen were found on the surface of rabbit skin after experimental injection of whole venom and sphingomyelinase D. The duration of recoverable antigen using this experimental model appears to be at least two weeks and as long as 21 days in some cases. CONCLUSIONS: Because the duration of the recoverable antigen is seen to be at least two weeks, the ELISA venom test appears capable of detecting venom on most patients presenting with Loxosceles envenomations. This detection system will allow the physician more accurate determination of whether the lesion is from a brown recluse spider or some other agent that can cause this type of necrotic ulcer.

Whole blood platelet aggregometry and platelet function testing.

Platelet aggregometry has been the reference method employed to detect, diagnose, and monitor qualitative platelet disorders since the early 1960s. Lumiaggregometry and impedance-based whole blood lumiaggregometry have advantages over light transmittance aggregometry in that they provide for enhanced specimen management and increase the test sensitivity to impairment of platelet granule secretion. Whole blood lumiaggregometry detects and identifies congenital and acquired platelet plasma membrane receptor defects, metabolic pathway secretion disorders, and storage pool deficiency. Whole blood lumiaggregometry is also being applied to antiplatelet therapy monitoring and identifies aspirin and thienopyridine resistance. There is growing interest in using impedance-based whole blood lumiaggregometry for near-patient whole blood platelet analysis and antiplatelet therapy monitoring. This article will also discuss other whole blood testing processes for assessing platelet function, particularly as applied to assessing the effect of antiplatelet medication.

Comparison of a chromogenic factor X assay with international normalized ratio for monitoring oral anticoagulation therapy.

The purpose of the present study was to compare the international normalized ratio with a chromogenic factor X (CFX) assay for monitoring patients on oral anticoagulant therapy using the DiaPharma CFX method on a STA-R Evolution coagulation analyzer. International normalized ratio values were correlated with the CFX for determining normal, subtherapeutic, therapeutic and supratherapeutic ranges for these patients. Specimens were analyzed and grouped as normal or patients on oral anticoagulant therapy with international normalized ratios of less than 2.0, 2.0-3.0, and more than 3.0. Three hundred and nine randomly selected oral anticoagulant therapy patients were tested. The range of international normalized ratio and CFX in oral anticoagulant therapy patients was 0.92-12.76 and 9-132%, respectively. CFX was inversely related to international normalized ratio; R = 0.964 (P < 0.0001) (CFX = 13.2 + (5.3/international normalized ratio) + (81.3/international normalized ratio). Results by group were as follows: normal (n = 30), CFX range 72-131%, mean CFX 96%; international normalized ratio less than 2.0 (n = 70), CFX range 32-132%, mean CFX 53%; international normalized ratio 2.0-3.0 (n = 135), CFX range 18-48%, mean CFX 28%; international normalized ratio more than 3.0 (n = 104), CFX range 9-46%, mean CFX 21%. Sensitivity and specificity crossed at a CFX of 35.5%, which yielded a sensitivity of 91.7% and a specificity of 91.9% for discriminating international normalized ratio of at least 2.0. Area under the curve on receiver-operator curve using international normalized ratio was 0.984 (P < 0.001). In this randomly selected group of oral anticoagulant therapy patients and normal individuals at varying levels of anticoagulation, CFX correlated well with international normalized ratio as determined by R = 0.964. The data suggests that the CFX can be a useful tool for monitoring oral anticoagulation in patient populations in which confounders to international normalized ratio may be present. Further investigation with the use of CFX for monitoring is warranted in large patient populations on oral anticoagulant therapy, including follow-up for clinical outcomes.

Comparison of four laboratory methods to assess aspirin sensitivity.

The purpose of this study was to compare the ability of four commercial platelet function assays to detect aspirin response in normal individuals taking 81 or 325 mg aspirin in a single-dose response and then in a 7-day dosing regimen. We employed the Chronolog 570VS whole-blood aggregometer with agonists 1.0 microgram/ml collagen and 0.5 mmol/l arachidonic acid, the PFA-100 epinephrine/collagen cartridge closure time, the Accumetrics Verify/Now arachidonic acid cartridge, and the urine 11-dehydrothromboxane immunoassay normalized to urine creatinine. Fifty normal individuals who met the inclusion criteria were consented in the single-dose study. Blood and urine were collected at baseline, and then each participant was given a 81 mg enteric-coated aspirin tablet. Blood and urine were collected after 24 h. After a minimum of 14 days the process was repeated with a 325 mg aspirin dose. Forty-five individuals were enrolled in the 7-day study. Blood and urine were collected at baseline. Then each participant was given an 81 mg dose of aspirin daily for 7 days. After 7 days, blood and urine specimens were obtained and tested. After a minimum washout period of 14 days the process was repeated using a 7-day regimen of 325 mg enteric-coated aspirin tablet. Student's t-test indicated statistical significance between baseline and post responses in both dosing regimens (P < 0.05). Individuals were not consistently identified as aspirin responsive across all platforms. All assays discriminated between platelet response and nonresponse to aspirin at both dosages. It may be necessary to employ multiple assays to detect individual platelet response.

Cutaneous and systemic effects of varying doses of brown recluse spider venom in a rabbit model.

OBJECTIVE: To ascertain whether a dose response exists between the dose of brown recluse spider venom (BRSV) and the cutaneous and coagulation effects in a rabbit model. Cutaneous necrosis is a serious complication of brown recluse spider envenomation (spider bite with venom). Disseminated intravascular coagulation (DIC) is a dreaded complication of brown recluse envenomation in humans. New Zealand white (NZW) rabbits have proved to be a model for the study of therapeutic regimens to prevent skin necrosis after spider bites. We studied the venom's effects on the skin and the coagulation mechanism in this rabbit model to determine if a clear dose-response relationship could be established. Establishment of a dose-response relationship is an important first step in determining if the NZW rabbit is a suitable model to study both cutaneous and systemic effects of the venom. DESIGN: Thirty-six NZW rabbits were divided into three groups. One group received a saline injection, and the other two groups received a 4.0 microg or a 10.0 microg dose of purified BRSV intradermally into the skin on the dorsum of the back. METHODS: Blood was collected at baseline, 24, 48, and 72 hours. Tissue specimens were obtained after seven days during the animal necropsy and gross and microscopic pathology examination was conducted to assess tissue damage. Measurements included complete blood count (CBC); platelets; PT; activated partial thromboplastin time (APTT); fibrinogen (clottable, immunological); coagulation factors II, V, VII, VIII, IX, X, XI, XII; anti-thrombin (AT); alpha-2 antiplasmin (AP); Protein C (PC); mixing studies; lupus anticoagulant screening; plasminogen; thrombin-antithrombin; fibrin degradation products (FDP); d-dimer; and thrombin time. RESULTS: Gross pathology results were consistent with previous studies that used higher doses of BRSV. The WBC and platelet counts decreased at 24 hours in the two groups receiving the BRSV (p < 0.05). BRSV produced a dose related prolongation in the APTT (p < 0.05). Levels of fibrinogen as well as factors V, VII, VIII, IX, X, AT, and AP (p < 0.05) were increased in response to the BRSV. Protein C decreased at 24 hours (p < 0.05) and remained low in other time points. Mixing studies corrected the prolonged APTTs to normal ranges. Factor IIXI and XII showed no significant alteration in response to the BRSV. CONCLUSIONS: In the model, both the size and depth of the eschar were dose-related. We also observed a dose related elevation in the APTT that corrected with mixing studies. The dose-response relationship suggests direct interference by a component of the venom, rather than an idiosyncratic response. We did not detect a deficiency of commonly measured coagulation factors or evidence of a lupus anticoagulant. Protein C demonstrated a decrease. Although DIC did not occur in this rabbit model, a dose-related elevation in APTT was noted. The finding that the elevation corrected with mixing studies suggests that a plasma factor is essential in the coagulopathy associated with brown recluse envenomation. Further studies to identify this factor could shed light on human coagulopathy following envenomation.

Comparison of colchicine, dapsone, triamcinolone, and diphenhydramine therapy for the treatment of brown recluse spider envenomation: a double-blind, controlled study in a rabbit model.

OBJECTIVE: To compare the efficacy of dapsone, diphenhydramine, colchicine, and intralesional triamcinolone in the treatment of brown spider bites. We used a purified venom that reproducibly produces a large eschar. To mimic real-life circumstances, all agents were administered following a 2-hour delay after envenomation. The animals were evaluated for the presence of coagulopathy to determine if the incidence of systemic findings correlated with the type of treatment. DESIGN AND SETTING: In a research laboratory, 60 New Zealand white rabbits each received an intradermal injection of 20 microg of purified Loxosceles reclusa venom. The rabbits were divided into 5 groups of 12; a control group and 4 groups treated with a drug (either colchicine, triamcinolone, diphenhydramine, or dapsone). Measured end points included maximum eschar size as well as histologic grading of depth, inflammation, and thrombosis. INTERVENTIONS: Treatment with colchicine, triamcinolone, diphenhydramine, or dapsone. MAIN OUTCOME MEASURES: Maximum eschar size as well as histologic grading of depth, inflammation, and thrombosis. RESULTS: There was no significant difference with respect to eschar size (1-way analysis of variance, P = .003). There was no significant difference between any treatment with respect to presence or absence of ulcer, necrosis, large vessel vasculitis, or small vessel vasculitis. The only outcome of significance was that triamcinolone offered protection from thrombosis (chi2 likelihood ratio, P = .04). We also noted evidence of coagulopathy in all of the envenomated animals. The rabbits had grossly elevated activated partial thromboplastin time results, which were corrected with 1:1 mixing with normal rabbit plasma, suggesting an acquired factor deficiency. We did not detect an individual factor deficiency or a lupus anticoagulant. CONCLUSIONS: In a rabbit model, none of the agents tested (dapsone, diphenhydramine, colchicine, and intralesional triamcinolone) had an effect on eschar size. Triamcinolone appeared to offer some protection against histologic evidence of thrombosis, but this protection did not translate into a difference in clinical outcome. All animals developed evidence of coagulopathy, regardless of treatment. The coagulopathy could be corrected by fresh rabbit plasma, suggesting an acquired factor deficiency.

Effects of pre-analytical variables on the anti-activated factor X chromogenic assay when monitoring unfractionated heparin and low molecular weight heparin anticoagulation.

The purpose of this study was to determine whether the anti-activated factor X (anti-FXa) assay is less affected by pre-analytical variables in monitoring patients on unfractionated heparin (UFH) and low molecular weight heparin (LMWH) than the activated partial thromboplastin time (aPTT). Forty-six subjects receiving either enoxaparin (LMWH) or UFH were randomly selected. Each study subject had six vacutainer tubes (3.8% sodium citrate, 3.2% sodium citrate) drawn by an atraumatic venipuncture. One tube from each set had a blood to anticoagulant ratio of 9: 1. The other tube had an intentional "short-draw" of approximately 6: 1 blood to anticoagulant ratio. All specimens had an aPTT and a chromogenic anti-FXa assay performed on each specimen regardless of heparin type. The aPTT assay mean with the 3.8% sodium citrate tube short-draw tube was statistically different from the other aPTT assays (P = 0.06). However, all six of the mean anti-FXa assays for the UFH and LMWH heparin subjects were not statistically or clinically different (analysis of variance, P = 0.9878 for UFH and P = 0.9060 for LMWH). The intentional short-draw tube did not affect the anti-FXa assay regardless of the anticoagulant. The anti-FXa assay appears to be a better method for monitoring heparin subjects than the aPTT due to the lack of effect of pre-analytical variables.

Antiphospholipid antibodies and stroke in young women.

BACKGROUND AND PURPOSE: Antiphospholipid antibodies have been associated with ischemic stroke in some but not all studies. METHODS: We performed a population-based case-control study examining antiphospholipid antibodies (anticardiolipin antibodies and lupus anticoagulants) using stored frozen sera and plasma in 160 cases and 340 controls enrolled in the Stroke Prevention in Young Women study. We evaluated for the presence of anticardiolipin antibody (IgG, IgM, and IgA isotypes) by an enzyme-linked immunosorbent assay and for the lupus anticoagulant using several phospholipid-dependent coagulation tests (activated partial thromboplastin time, dilute Russell's viper venom time) with mixing studies. If mixing studies were prolonged, confirmatory tests were performed. RESULTS: A positive anticardiolipin antibody level of any isotype was seen in 43 cases (26.9%) and 62 controls (18.2%) (P=0.03), lupus anticoagulant in 29 cases (20.9%) and 38 controls (12.8%) (P=0.03), and either anticardiolipin antibody or lupus anticoagulant in 61 cases (42.1%) and 86 controls (27.9%) (P=0.003). After adjustment for age, current cigarette smoking, hypertension, diabetes, angina, ethnicity, body mass index, and high-density lipoprotein levels, the relative odds of stroke for women with anticardiolipin antibody immunoreactivity of any isotype or a lupus anticoagulant was 1.87 (95% confidence interval, 1.24 to 2.83; P=0.0027). CONCLUSIONS: The results from this study support the importance of antiphospholipid antibodies as an independent risk factor for stroke in young women.

Facilitation of recovery from acute blood loss with hyperbaric oxygen.

BACKGROUND: Hyperbaric oxygen (HBO) has been used for more than 25 years as therapy for extreme blood loss in cases where transfusion has been unavailable. The use of HBO for lesser amounts of blood loss to avoid the transfusion of blood products has not been investigated. HYPOTHESIS: Hyperbaric oxygen up-regulates hemoglobin synthesis after acute blood loss in an animal model of moderate (30%) blood loss. DESIGN: Twenty-four New Zealand white rabbits were bled to a calculated loss of 30% of the circulating blood volume. The rabbits received Ringer lactate infusions to correct hypovolemia and were divided into 2 groups: a control group and a treatment group receiving HBO. INTERVENTION: One group of 12 animals received no treatment other than Ringer lactate resuscitation, whereas the other group of 12 received 5 HBO treatments in the 4 days immediately following blood loss. Hemoglobin levels and reticulocyte counts were monitored for 14 days after the bleeding episode. RESULTS: The control group was more affected by the blood withdrawal than the HBO group, reaching a low of 37% hemoglobin loss compared with 29% hemoglobin loss at 48 hours (P<.001). The HBO group recovered faster, reaching the baseline level of hemoglobin in 11 days as opposed to 14 days for the control group (P<.001). Reticulocyte counts were not significantly affected by HBO treatment. CONCLUSIONS: Treatment with HBO favorably affected recovery from moderate (30%) acute blood loss, resulting in lessened effects at 48 hours and hastening recovery to baseline hemoglobin levels. Our results support the data gained from clinical experience treating extreme blood loss with HBO.

A comparison of INRs after local calibration of thromboplastin international sensitivity indexes.

UNLABELLED: There are approximately 300 reagent/instrument combinations for performing prothrombin times/international normalized ratios (PT/INR) in the United States. Manufacturers and laboratories continually struggle to ensure that the International Sensitivity Index (ISI) of their thromboplastin is accurate for assaying PT/INR. OBJECTIVE: This study reports the feasibility of a new method to locally calibrate ISI of thromboplastin using the mechanical STA automated coagulation analyzer (Diagnostica-Stago Inc.) and two photo-optic coagulation analyzers, the BCS (Dade-Behring) and CA-540 (Sysmex). DESIGN: Neoplastine CI+ (CI+) (Diagnostica-Stago Inc); Thromboplastin C+ (TC+); Thromborel S (TRS); and Innovin (I) (Dade-Behring) were used in this study. A mean normal PT (MNPT) was determined for each reagent/instrument combination using samples from 25 normal individuals. Manufacturer instrument specific ISI values were not available for the STA with TC+, TRS and I. The CA540 had no ISI value for CI+ and the BCS system had no manufacturer assigned ISI values for TC+ and I; generic photo-optic and mechanical ISI manufacturer values were used for these two systems. Local on-site calibration was performed using frozen plasma calibrators to determine ISI values for each thromboplastin. Post-calibration, 95 patient samples were assayed for each reagent/instrument system combination using the manufacturer ISI and the local calibrated ISI to determine the INR result. PATIENTS: Patients from whom samples were obtained included five with a lupus anticoagulant, 30 on heparin therapy, and 60 on coumadin therapy. RESULTS: Differences between manufacturer versus local calibrated ISI ranged from 0.9% to 18.9% for normal sample INRs and from 0.8% to 16.4% for patient sample INRs. The number (or proportion) of patient specimens with clinically significantly different INR values (>10.0% difference) ranged from zero for several reagent combinations to more than half (or >50.0%) of those tested for several other combinations. CONCLUSION: Our results indicated that by locally calibrating ISI values, each laboratory may eliminate variability and guesswork between different reagent/instrument systems for ISI values when performing PT/INR assays and potentially improve the clinical accuracy of their patients' PT/INR results.