Hyperimmune globulins and same-day thrombotic adverse events asrecorded in a large healthcare database during 2008–2011

Mikhail Menis,1 Gayathri Sridhar,2* Nandini Selvam,2 Mikhail V. Ovanesov,1 Hozefa A. Divan,2

Yideng Liang,1 Dorothy Scott,1 Basil Golding,1 Richard Forshee,1 Robert Ball,1

Steven A. Anderson,1 and Hector S. Izurieta1

Thrombotic events (TEs) are rare serious complications following administration of hyperimmune globulin(HIG) products. Our retrospective claims-based study assessed occurrence of same-day TEs following admin-istration of HIGs during 2008–2011 and examined potential risk factors using HealthCore’s IntegratedResearch Database (HIRDSM) and laboratory testing of products’ procoagulant Factor XIa activity by U.S.Food and Drug Administration. Multivariable regression was used to estimate same-day TE risk for differentproducts. Of 101,956 individuals exposed to 23 different HIG product groups, 86 (0.84 per 1,000 persons) hada TE diagnosis code (DC) recorded on the same day as HIG administration. Unadjusted same-day TE DC rates(per 1,000 persons) ranged from 0.4 to 148.9 for different products. GamaSTAN S/D IG >10 cc had statisticallysignificantly higher same-day TE DC risk compared to Tetanus IG (OR 5 57.57; 95% CI 5 19.72–168.10).Increased TE risk was also observed with older age (�45 years), prior thrombotic events, and hypercoagulablestate(s). Laboratory investigation identified elevated Factor XIa activity for GamaSTAN S/D, HepaGam B,HyperHep B S/D, WinRho SDF, HyperRHO S/D full dose, and HyperTET S/D. Our study, for the first time, identi-fied increase in the same-day TE DC risk with GamaSTAN S/D IG >10 cc and suggests potentially elevated TErisk with other HIGs. Am. J. Hematol. 88:1035–1040, 2013. VC 2013 Wiley Periodicals, Inc.

IntroductionImmune globulin (IG) products are plasma-derived prod-

ucts used for treatment of immune deficiencies, immunethrombocytopenia, multiple sclerosis, myasthenia gravis,and many other health conditions [1–7]. Currently, thereare multiple commercial IG preparations that differ bylabeled indications, manufacturing processes, and formula-tion [2,8–10]. Hyperimmune globulins (HIGs) are manufac-tured from donor plasma containing high concentrations ofantibodies to specific antigens and used for prophylaxis ortreatment of specific diseases (e.g., hepatitis B, cytomega-lovirus, tetanus, rabies). The HIGs include, among others,Cytomegalovirus IGIV, Hepatitis B IGIV, RhoD IGIV, andTetanus IG [8,9,11,12]. Overall, IG use is considered safeand effective, but serious and potentially fatal adverseevents may occur and include thrombotic complications,anaphylaxis, hemolysis, and acute renal failure [2,4,12–17].

The withdrawal of Octagam and recall of Omr-IgG-amTM

from U.S. and foreign markets because of increased occur-rence of thrombotic events (TEs), as well as findings of anincreased TE risk with Vivaglobin prompted us to examinesafety of HIG products [18–23]. Our recent retrospectiveclaims-based investigation of IGs, for the first time, led to theidentification of a possible increased TE risk with Vivaglobin,a subcutaneous product, and raised attention regardingpotentially elevated procoagulant content of some IGs[22,24]. TEs due to IG products are likely to be acute, occur-ring within 24 hours of administration, and potential underly-ing risk factors may include recipient predispositions (e.g.,age, previous TEs) and product factors (e.g., dosage, infu-sion rates, manufacturing processes) [4,14,15,17,22,25–30].Therefore, the U.S. Food and Drug Administration’s (FDA)Center for Biologics Evaluation and Research (CBER) andHealthCore conducted an epidemiologic study to assess andcompare the occurrence of same-day TEs following adminis-tration of different U.S.-licensed HIG products and ascertainrisk factors for HIG-related TEs, using a large healthcaredatabase. Additional laboratory testing of HIG products wasconducted by CBER to assess procoagulant Factor XIa(FXIa) activity as a potential biochemical root cause of TEs.

Materials and Methods

Study design

A retrospective claims-based cohort analysis was conducted usingHealthCore’s Integrated Research Database (HIRDSM), a longitudinalhealthcare database. It includes enrollment information and claims datafor approximately 69 million members with medical eligibility in the U.S.covered by Blue Cross and/or Blue Shield licensed plans across severalstates. Claims data capture medical services rendered, including patientdiagnoses and procedures, during a visit to either the physician office ora hospital; enrollment data helps to ascertain coverage eligibility and pro-vides information on demographic characteristics. HIRDSM is also a partof Congressionally mandated Sentinel System currently being developedby FDA to conduct active surveillance of medical product safety in theUnited States [31,32]. Overall, the HIRDSM population approximates theUS population well, with the HIRDSM population being slightly youngersince all members are commercially insured [33].

All individuals exposed to HIGs from January 1, 2008 through August31, 2011 were selected into the study cohort. The study received waiverof consents to utilize claims data from FDA and HealthCore’s institutionalreview boards. Additionally, the cohort included persons exposed to Syn-agis

VR

, the first monoclonal antibody product for infectious disease, whichreplaced HIG RSV IGIV product [11,34,35]. The HIG products assessedwere determined based on the occurrence of at least one claim withrecorded Healthcare Common Procedure Coding System (HCPCS) orCurrent Procedural Terminology (CPT) code(s) of interest and included:Botulism IGIV; Botulinum antitoxin, equine; CMV (Cytomegalovirus)IGIV; Diptheria antitoxin, equine; GamaSTAN S/D IG 1–10 cc;

Additional Supporting Information may be found in the online version of thisarticle.1Center for Biologics Evaluation and Research, U.S. Food and Drug Admin-istration, Rockville, Maryland; 2HealthCore Inc, Alexandria, Virginia

*Correspondence to: Gayathri Sridhar; HealthCore Inc., 2001 N. BeauregardStreet, Suite 500, Alexandria, VA 22311.E-mail: gsridhar@healthcore.com

Contract grant sponsor: U.S. Food and Drug Administration, Center for Bio-logics Evaluation and Research.

Received for publication 2 May 2013; Revised 28 June 2013; Accepted 22July 2013

Am. J. Hematol. 88:1035–1040, 2013.

Published online 1 August 2013 in Wiley Online Library(wileyonlinelibrary.com).DOI: 10.1002/ajh.23559

VC 2013 Wiley Periodicals, Inc.

American Journal of Hematology http://wileyonlinelibrary.com/cgi-bin/jhome/351051035

Research Article

GamaSTAN S/D IG >10 cc (high dose); Hepatitis B IGIM; Hepatitis BIGIV; Lymphocyte IG 25 mg (rabbit); Lymphocyte IG 250 mg (equine);Rabies IG; Rabies IG HT; RSV (Respiratory Syncytial Virus) IGIM; RSVIGIV; RhoD IG (Rhophylac); RhoD IGIV SD; RhoD IG minidose (250 IU);RhoD IG full dose (1500 IU); RhoD IGIV; Tetanus IG; Varicella ZosterIGIM; and Vaccinia IGIM. The HIG users were classified into mutuallyexclusive single- and multiple-product user groups, based on therecorded product usage during the study period. As the TE outcome israre, there was no continuous eligibility requirement prior to firstobserved HIG exposure in order to allow for the maximum number ofexposed individuals to be included in the study.

Demographics, including age at first HIG exposure and gender,were obtained from beneficiary enrollment data. Baseline risk factorsfor TEs, including prior history of TEs, hypertension, dyslipidemia,gammopathy, obesity, hypercoagulable state, other inflammatory condi-tions [36], pregnancy, oral contraceptive use, and estrogen replace-ment therapy were evaluated using ICD-9-CM diagnosis, CPT, andNDC codes recorded on medical and pharmacy claims up to 6 monthsprior to the first HIG exposure. Potential indications for HIG productswere evaluated 30 days prior to the first HIG exposure. The ElixhauserComorbidity Index (ECI) [37–39] was measured for a period of 12months prior to the first HIG exposure.

Study end point

TEs, arterial and venous, were identified based on ICD-9-CM diag-nosis codes recorded on medical claims and further evaluated as acomposite outcome. Arterial TE diagnosis code(s) (DCs) includedacute myocardial infarction (MI), acute coronary occlusion without MI,occlusion of precerebral or cerebral arteries, transient cerebral ische-mia, arterial embolism/thrombosis, atheroembolism, acute vascularinsufficiency of intestine, vascular myelopathies, retinal vascular occlu-sion, hepatic infarction, and renal vascular embolism/thrombosis.Venous TE DCs included pulmonary embolism and infarction, venousembolism and thrombosis, phlebitis and thrombophlebitis, thrombosisof intracranial venous sinus, and portal vein thrombosis. Primary analy-ses evaluated TE DCs recorded on the same day as HIG exposuressince TEs are likely to be acute.

CBER laboratory analysis

The available unexpired samples of HIG products were purchasedfrom NIH Pharmacy in July–August, 2012. Since previous investiga-tions identified coagulation FXIa as main procoagulant impurity associ-ated with thrombotic adverse events [40], FXIa activity assays, in-house Thrombin Generation Assay (TGA) and commercial FXIa Activ-ity Chromogenic Assay (CA), were used to characterize products.

In-house TGA was performed as described in Shibeko et al. [41]with minor modifications. Specifically, human Factor XI-deficient plasma(75% vol/vol, George King Bio-Medical, Overland Park, Kansas orAffinity Biologicals, Ancaster, ON, Canada) was mixed with fluorogenicsubstrate for thrombin ZGGR-AMC (Bachem, Torrance, CA), phospho-lipid vesicles (4 mM, Rossyx), tissue factor (0.3 pM, Innovin, Baxter),and serially diluted IG samples or calibrator FXIa. In-house softwarewas used to calculate parameters of thrombin generation responseafter recalcification with calcium chloride (12.5 mM). Maximal rate offluorescent increase (also known as maximal thrombin peak height)was used as assay readout.

Biophen FXIa Activity CA (Aniara, West Chester, OH) was con-ducted according to manufacturer recommendation with our in-housecalibrator. Maximal rate of substrate conversion was used as assayreadout. In both assays, FXIa activity was calculated by comparingserially diluted samples against a calibration curve made with a purifiedFXIa standard (Haematologic Technologies, Essex Junction, VT). TheNIBSC international reference reagent for activated blood coagulationFXIa 11/236 (National Institute for Biological Standards and Control,Hertfordshire, UK) was included as a control in each assay.

Statistical analysis

Baseline characteristics for different HIG product users includingdemographics and other potential TE risk factors were compared usingchi-square tests for categorical variables and ANOVA for continuousvariables. The crude incidence rates were estimated for the same-dayTE DCs (per 1,000 persons exposed) overall, and by age, gender, andspecific HIG products. Also, baseline TE rates were assessed on theday prior to the exposure for each of the HIG product groups. Logistic

regression analysis was used to assess the effect of different HIGs onTE DC occurrence as compared to Tetanus IG and to estimate theodds ratios (ORs) and 95% confidence intervals (95% CIs), while con-trolling for potential confounders. Tetanus IG was chosen as the refer-ence category as this group comprised the largest number of singleproduct users of all age groups. Regression analyses were based onlyon those exposure product groups that had at least one same-day TEDC recorded during study period. It was decided a priori to retain age,gender, and a comorbidity measure (ECI) regardless of their statisticalsignificance as these variables are biologically and clinically important.All analyses were conducted using SAS version 9.2.

Preplanned sensitivity analyses

Propensity score (PS) modeling was done to account for confound-ing by indication. The HIG products of interest, GamaSTAN S/D IG>10 cc, Lymphocyte IG 25 mg (rabbit), RhoD IGIV SD and Hepatitis BIGIV, were compared to Tetanus IG, one at a time. PS was used inseveral ways in the outcome models including 1:4 matching and in theregression model either as a continuous or a quintile variable [42]. Inthe 1:4 matching, each person exposed to the product of interest wasmatched to four persons exposed to Tetanus IG by the similar range ofpropensity score. After ensuring balance between the exposure groups,the ORs and 95% CIs were estimated.

Additional sensitivity analyses of same- or next-day and next-day TEDC outcome recorded following HIG exposure were conducted toassess the risk window duration, as it is possible that events occurringwithin 24 hours after exposure(s) were recorded on the following day.Furthermore, as same-day TE DCs may be just recorded histories ofprior TE(s), we conducted a conservative-approach sensitivity regres-sion and PS analyses which excluded claims with the same-day TEDCs if there was a 30-day prior history of any TE(s).

ResultsThe study identified 101,956 individuals exposed to 23

different HIG product groups during 2008–2011. Baselinecharacteristics for the 10 HIG product user groups with atleast one same-day TE DC recorded during the studyperiod differed significantly by demographic characteristics(e.g., age, gender), ECI, and histories of health conditions(Supporting Information eTable I). Among 101,956 individu-als exposed to HIGs, 86 (0.8 per 1,000) had same-day TEDCs recorded, with unadjusted rates (per 1,000) rangingfrom 0.4 for RhoD IG full dose (1500 IU) to 148.9 forGamaSTAN S/D >10 cc (Supporting Information eTable II;Fig. 1). The TE DC rates by age groups were 0.5 for indi-viduals less than 15 years of age, 0.4 for 15–44 years, 3.3for 45–64 years, and 6.5 for 65 years and older (SupportingInformation eTable II). The results on next-day TE DCoccurrence showed much lower rates per 1,000 personsexposed overall, by product, and by demographic charac-teristics (Supporting Information eTable III). Of 86 HIGusers with same-day TEs, about 56% were ages 45 andover, nearly 59% were females, 45% had prior TE, andabout 5% had a history of hypercoagulable state (Support-ing Information eTable IV). The study identified equal num-ber of arterial and venous events recorded with theircorresponding TE DC rates varying by products and demo-graphic characteristics (Supporting Information eTable II).Compared to HIG users with venous TEs, those with arte-rial TEs were more likely to be ages 45 and over (70% vs.42%), have history of hypertension (56% vs. 19%) andhigher ECI (3.0 vs. 1.6) (Supporting Information eTable IV).TE outcome distribution analysis showed occurrence ofespecially serious same-day TE DCs (e.g., MI, pulmonaryembolism and infarction, venous embolism and thrombosis)for GamaSTAN S/D >10 cc (data not shown).

Table I displays results of the primary, overall andgender-based, multivariable logistic regression analyses,which demonstrated statistically significant increased oddsof same-day TE DCs for GamaSTAN S/D IG >10 cc(OR 5 57.57; 95% CI 5 19.72–168.10) and Lymphocyte IG

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25 mg (Rabbit) (OR 5 6.22; 95% CI 5 2.03–19.04) com-pared to Tetanus IG. Hepatitis B IGIV and RhoD IGIV SDhad elevated but not statistically significant same-day TEDC risk, (OR 5 6.98; 95% CI 5 0.82–59.37 and OR 5 2.52;95% CI 5 0.99–6.40, respectively) (Table I). PS analysesyielded results consistent with the overall analysis for theproducts evaluated, except for Lymphocyte IG 25 mg (Rab-bit) which showed an elevated but nonsignificant TE risk(Supporting Information eTable V). The overall analysisalso showed significantly elevated TE risk for HIG usersages 45 and older (OR 5 3.30; 95% CI 5 1.44–7.54), withprior TEs (OR 5 26.29; 95% CI 5 14.89–46.40), and hyper-coagulable state (OR 5 3.45; 95% CI 5 1.09–10.92) (TableI). Gender-based, same- or next-day, and conservative

approach (i.e., same-day TE with no 30-day prior TE his-tory) models consistently showed significantly elevated TEDC risk for GamaSTAN S/D IG >10 cc (Table I; Fig. 2). Inthe next-day analysis, except for RhoD IGIV SD(OR 5 3.80; 95% CI 5 1.09–13.22), none of the HIGs werefound to have a significantly elevated TE DC risk, suggest-ing the importance of same-day TEs (Fig. 2).

Table II shows results of CBER’s laboratory analysis ofFXIa activity for HIG products using in-house TGA and com-mercial FXIa Activity CA. Compared to FXIa concentration ofabout 70 pM in the TE-implicated lot used as control, theLymphocyte IG 25 mg (Thymoglobulin, rabbit-derived), RSVmonoclonal antibody (SynagisVR ), and Cytomegalovirus IGdemonstrated low procoagulant activity (around 1 pM of

Figure 1. Unadjusted same-day TE diagnosis code rates per 1000 persons exposed by the 10 HIG product groups.

TABLE I. Primary Analyses: Association between the 10 HIG Product Groups and Risk of the Same-Day TE Diagnosis Code(s) Recordeda

Adjusted O!R (95% CI)

Categories Crude OR (95% CI) Overallb Femalesc Malesd

Cohort size 90,961 78,524 11,913Single HIG products

Tetanus IG 1.00 1.00 1.00 1.00CMV IGIV 3.15 (0.75, 13.28) 1.01 (0.22, 4.57) 0.69 (0.08, 5.76) 2.01 (0.24, 17.11)GamaSTAN S/D IG 1–10 cc 0.84 (0.26, 2.76) 0.96 (0.29, 3.20) 1.47 (0.41, 5.23) NAe

GamaSTAN S/D IG >10 cc 62.26 (25.78, 150.39)f 57.57 (19.72, 168.10)f 38.77 (7.89, 190.43)f 99.78 (22.89, 435.01)f

Hepatitis B IGIV 7.41 (0.99, 55.52) 6.98 (0.82, 59.37) NAe 10.36 (1.22, 87.75)f

Lymphocyte IG 25 mg (rabbit) 9.78 (3.74, 25.54)f 6.22 (2.03, 19.04)f 2.69 (0.24, 29.68) 13.71 (3.71, 50.71)f

RSV IGIM 0.27 (0.12, 0.59)f 0.95 (0.33, 2.79) 0.18 (0.02, 1.76) 1.52 (0.40, 5.81)RhoD IGIV SD 2.22 (0.92, 5.37) 2.52 (0.99, 6.40) 1.08 (0.23, 5.11) 5.97 (1.79, 19.88)f

RhoD IG full dose (1500 IU) 0.13 (0.08, 0.22)f 0.66 (0.26, 1.63) 0.45 (0.13, 1.48) 5.31 (1.10, 25.71)f

Multiple HIG Products 0.20 (0.03, 1.49) 0.90 (0.11, 7.14) 0.84 (0.09, 7.78) NAe

Age in yearsAt least 45 10.54 (6.88, 16.14)f 3.30 (1.44, 7.54)f 2.15 (0.69, 6.70) 3.27 (1.04, 10.29)f

SexFemale 0.27 (0.17, 0.41)f 0.84 (0.49, 1.42)

ECI 1.57 (1.47, 1.68)f 0.98 (0.87, 1.11) 1.04 (0.89, 1.21) 0.90 (0.75, 1.08)Prior TE 73.13 (47.64, 112.25)f 26.29 (14.89, 46.40)f 39.29 (18.35, 84.12)f 16.71 (7.22, 38.64)f

Hypercoagulable state 18.37 (6.69, 50.46)f 3.45 (1.09, 10.92)f 4.67 (1.22, 17.95)f NAg

OCP/ERT use 1.08 (0.25, 4.61)

CI indicates confidence interval; ECI, Elixhauser Comorbidity Index; HIG, Hyperimmune globulin; OCP/ERT, oral contraceptive/estrogen replacement therapy; OR,odds ratio; TE, thrombotic event.

a Data are reported as odds ratio (95% confidence interval).b Primary overall analysis for same-day TE diagnosis code.c Primary analysis for same-day TE diagnosis code among females.d Primary analysis for same-day TE diagnosis code among males.e There were no TE diagnosis code(s) on the same day as the exposure for this product groupf P<0.05.g Hypercoagulable state did not make it into the final model during the model building process for males.

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FXIa). Oppositely, GamaSTAN S/D, HepaGam B, HyperHepB S/D, WinRho SDF, HyperRHO S/D full dose, and Hyper-TET S/D contained elevated FXIa activity, between 79 and444 pM of FXIa (in-house TGA), which was close to a rangeof 100–300 pM previously found in thrombosis-associatedlots of 5% IGIV product in 2010 [40].

DiscussionOur retrospective claims-based cohort study consistently

identified a significantly increased same-day TE DC riskamong individuals exposed to GamaSTAN S/D high-dose(>10 cc) compared to Tetanus IG. The study also suggestedelevated same-day TE risk for Hepatitis B IGIV and RhoDIGIV SD. Our large database analyses showed increased TEDC risk for individuals ages 45 and over, with hypercoagulablestate(s), or history of TEs, which is generally consistent withthe literature [14,15,17,27,28]. Although initial results showedan elevated TE DC risk for Lymphocyte IG 25 mg (rabbit), itsindication (treatment of renal transplant rejection) made it par-ticularly susceptible to confounding by indication, and the pro-pensity score analyses showed nonsignificant results and,moreover, the FXIa activity for this product was found to below. In contrast, the same-day TE risk for GamaSTAN S/D>10 cc remained significantly elevated for all primary analy-ses (overall and gender-based) as well as the sensitivity anal-yses, including: same- or next-day analysis, PS analyses andthe conservative-approach analysis. Similar to the study’sdatabase findings, CBER’s laboratory investigation of pur-chased HIG product lots identified elevated Factor XIa activityfor GamaSTAN S/D, Hepatitis B IGIV (HepaGamB), andRhoD IGIV SD (WinRho SDF). Additionally, laboratory find-ings showed elevated FXIa activity for HyperHep B S/D,HyperRHO S/D full dose and HyperTET S/D.

The study findings show a wide variation of same-day TEDC rates for different HIG products, with nonzero rates rang-ing from 0.04% to 14.9%, which is consistent with existing lit-erature showing TE rate variation from 0.6% to 13%following IG exposure [15,22,27,43–47]. The study resultsshowed equal number of IG exposed persons with the same-day arterial versus venous TE DCs; and although some liter-ature suggests that arterial TEs are more likely to be acute,there are studies showing occurrence of mostly acutevenous events following IG exposure [15,27,28,43–45]. Ourstudy also showed that TE DC rates on the next day werelower than on the same day as exposure, suggesting impor-tance of the same-day occurrence of HIG-related TEs. More-over, baseline TE rate analyses identified no TE outcomeson the day prior for 21 of 23 HIG product groups and onlyone TE outcome each for the two remaining groups.

As supported by CBER’s laboratory findings of elevatedFXIa activity for different HIGs, the manufacturing processesmay result in an increased thrombotic potential of the prod-ucts likely because of unintentional copurification and con-tact activation of clotting factors (e.g., FXIa) [25,30,48,49].The published literature identified FXIa as a major biochemi-cal root cause of TEs in the implicated IG batches and sug-gested implementation of corrective measures into the IGmanufacturing processes to reduce FXIa-related procoagu-lant activity [40,50,51]. Finally, the identified differences inthe effect of HIGs on occurrence of TEs may be because ofmultiple factors, including manufacturing processes resultingin elevated FXIa activity, demographic characteristics (e.g.,older age, potential gender-based differences), underlyinghealth conditions (e.g., prior TE), dosing, rates, and routesof administration, which need further clinical investigation.

The study findings are based on claims data, and conse-quently limitations include potential under- or misrecordingof HIG product administrations and TE DCs as well as lackF

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1038 American Journal of Hematology

of clinical details to validate recorded outcomes, exposures,and risk factors. The validity of the recorded outcomes andexposures may differ by code, thus causing potential differ-ential misclassification bias. Multiple labeled and off-labeluses for different IG products, especially for GamaSTANS/D (e.g., Hepatitis A, Measles, Varicella, Immunodeficien-cies), and underlying TE risk factors, likely for users ofLymphocyte IG (rabbit), may have resulted in unadjustedconfounding by indication and could have affected studyfindings. The Elixhauser Comorbidity Index (ECI) utilized inregression analyses may not have captured well all thecomorbidities that may affect the HIG-related TE risk. Also,claims databases do not fully capture clinical details suchas product dosages, indications, administration rates androutes. Therefore, we cannot exclude the possibility thatour findings could be explained in part by an incorrect routeof administration or by the off-label use of the products.Finally, as specific temporality between exposure andsame-day TE cannot be measured using claims data andproduct lots evaluated by the laboratory could not be linkedto the database, additional clinical and laboratory investiga-tions are needed to help better understand and elucidateprecise timing and reasons for HIG-related TEs.

To our knowledge, this is the first retrospective claims-based cohort study to investigate the association betweenHIGs and TEs, and ascertain potential risk factors usinglarge private healthcare database. Despite its limitations,our study, for the first time, identified a likely associationbetween high doses of GamaSTAN S/D and occurrence ofTEs. The study also suggests an association betweenadministration of other HIG products (e.g., Hepatitis B IGIV,RhoD IGIV SD) and TE occurrence. The laboratory investi-gation showed elevated Factor XIa activity in the sameproducts, except for Lymphocyte IG 25 mg (rabbit), andidentified additional products with elevated FXIa activity:HyperHep B S/D, HyperRHO S/D full dose, and HyperTETS/D. Although direct comparison of thrombotic risks fortested products is difficult because of differences in dosing,strengths, routes and rates of administration, underlyingpatient risk factors, and lot-to-lot variability, laboratoryresults suggest elevated factor FXIa activity as a potentialbiochemical root cause for the elevated TE risk. The labo-ratory investigation also for the first time reported the datain units of international standard activity. Specifically, theactivity of the TE-implicated lot appears to be equivalent toa 0.08 U/mL of international standard. Despite the potential

assay limitations, the respective mass concentration ofFXIa in the TE-implicated lot of 70 pM appears to be com-parable with a previously reported range of 100–300 pMfound in other thrombosis-associated lots [40]. Furtherthrombogenicity studies of TE-implicated lots by manufac-turers should allow refinement of unsafety limit.

Overall, in addition to FXIa activity as a potential biochem-ical root cause of HIG-related TEs, our study suggests theimportance of underlying risk factors (e.g., demographics,health conditions) in development of HIG-related TEs. Ourstudy, in support of recent warnings of elevated TE risk withspecific products (e.g., GamaSTAN S/D, HepaGam B), sug-gests that risks vs. benefits should be weighed before HIGsare given to patients of ages 45 and over, with hypercoagu-lable state(s), or history of TEs [52,53]. The study alsostrongly suggests a substantially increased TE risk with highHIG dosages, especially for product(s) with elevated procoa-gulant activity. Finally, our study, along with other literature,suggest the need to further examine and, as needed, insti-tute changes in HIG manufacturing purification processesand introduce appropriate FXIa activity testing to helpimprove IG safety [25,30,40,48–51]. The ensemble of ourepidemiological and laboratory findings suggest: possibilityof class effect related to the presence of procoagulant activ-ity in multiple HIGs, need to further investigate impact oflarge HIG doses on TE risk, and evaluate the risk-benefit forindications requiring use of large product doses. In sum-mary, our retrospective cohort study demonstrates utility oflarge healthcare databases and concurrent laboratory inves-tigations for the timely detection, assessment, and verifica-tion of rare biologic product safety issues as well asascertainment of potential risk factors and identification andimplementation of prevention strategies.

Author ContributionsStudy concept and design: M.M., H.S.I., N.S., G.S., and

H.A.D. Acquisition of data: G.S., H.A.D., N.S., M.M., andH.S.I. Analysis and interpretation of data: G.S., H.A.D.,N.S., M.M., H.S.I., S.A.A., R.F., D.S., M.V.O., Y.L., B.G.,and R.B. Drafting of the manuscript: M.M., H.S.I., G.S.,H.A.D., and N.S. Critical revision of the manuscript forimportant intellectual content: N.S., G.S., H.A.D, M.M.,H.S.I., S.A.A., D.S., M.V.O., B.G., R.F., and R.B. Statisticalanalysis: G.S. and H.A.D. Obtaining funding: N.S., G.S.,M.M., H.S.I., S.A.A., and R.B. Administrative, technical or

TABLE II. Procoagulant Activity in HIG Products: Average and Standard Deviation (SD) based on Three Individual Experiments

FXIa activityc in undiluted product

ThrombinGeneration

AssayChromogenic

Assay

Brand name Classa Manufacturer Vial size Strengthb Average SD Average SD

Thrombotic Event-implicated lot IGIV Not specified 200 mL 5% 69.2 10.4 72.2 18.4HyperHep B S/D Hepatitis B IGIM Talecris 5 mL 15–18%, >220 IU/mL 134.6 15.9 136.1 25.0HyperHep B S/D neonatal Hepatitis B IGIM Talecris 0.5 mL Syringe 15–18%, >220 IU/mL 130.4 12.8 150.0 27.8

GamaSTAN S/D IGIM Talecris 2 mL 15–18% 102.5 13.7 110.4 13.7HyperRHO

VR

S/D Full Dose RhoD IGIM Talecris Syringe 1500 IU 374.6 47.6 412.4 101.3HyperTET

VR

S/D Tetanus IGIM Talecris Prefilled syringe 250 unit 443.7 55.1 488.8 108.3WinRho

VR

SDF RhoD IGIV SD Cangene 1.3 mL 1500 IU 98.9 12.3 106.8 19.9HepaGam B

VR

Hepatitis B IGIV Cangene 1 mL >312 IU/mL 79.1 9.6 81.7 18.1Thymoglobulin Anti-thymocyte Globulin (rabbit)

or ‘Lymphocyte IG 25 mg’Genzyme 5 mL 5 mg/mL <1 <1

Synagis (Palivizumab) RSV monoclonal antibody MedImmune 0.5 mL 50 mg <1 3.3CytoGam Cytomegalovirus IGIV CSL Behring 2.5 g/50 mL 5% 0.4 0.1 0.6 0.0

FXIa standard NIBSC 11/236 Pure FXIa NIBSC 1 mL 10 FXIa Units/mL 5668.8 524.5 4 970.4 792.2

a IG, immune globulin; IM, intramascular; IV, intravascular.b Labeled strength is expressed as immune globulin protein concentration (1% corresponds to 1 g of IG per 100 mL) and units of antibody activity, where possible.c Factor XIa activity is the concentration units of FXIa calibrator, picomoles per liter found in undiluted product.

research article

American Journal of Hematology 1039

material support: G.S., H.A.D., N.S., M.M., H.S.I., S.A.A.,R.F., M.V.O., D.S., and R.F. Study supervision: N.S., G.S.,M.M., H.S.I., R.F., S.A.A., B.G., and R.B.

AcknowledgmentsThe authors thank Dr. Joseph Singer, MD, HealthCore Inc.

for the clinical expertise and helpful recommendations duringthe design of the study.

Conflict of interestNothing to report.

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research article

1040 American Journal of Hematology