Search

Serum specimens submitted for confirmation of hepatitis B antigen (HBsAg) reactivity were tested by counterelectrophoresis (CEP) and by three modifications of the solid phase radioimmunoassay "sandwich" technique (SPRIA). In addition, the specificity of each reaction was determined for two of the SPRIA test methods. One hundred seventy-five of the 688 specimens were reactive by all techniques and a further 60 ere specifically reactive by two of modifications of SPRIA. An additional five specimens were positive by a third SPRIA modification. The primary SPRIA technique, using a homologous guinea pig antibody sandwich, detected 184 nonspecific reactive samples. With the same test done at 45C with a reduced incubation time, there were only 37 nonspecific reactive samples. None of the nonspecific samples was detected when the SPRIA technique used a heterologous guinea pig-human antibody sandwich. The results provide a basis for estimating the effectiveness of the SPRIA technique for HBsAg testing.

Transfusion-related acute lung injury (TRALI) mitigation strategies include the deferral of female donors from apheresis platelet (PLT) donations and the distribution of plasma for transfusion from male donors only. We studied the implications of these policies in terms of component loss at six blood centers in the United States.We collected data from allogeneic blood donors making whole blood and blood component donations during calendar years 2006 through 2008. We analyzed the distribution of donations in terms of the sex, transfusion and pregnancy histories, and blood type.A TRALI mitigation policy that would not allow plasma from female whole blood donors to be prepared into transfusable plasma components would result in nearly a 50% reduction in the units of whole blood available for plasma manufacturing and would decrease the number of type AB plasma units that could be made from whole blood donations by the same amount. Deferral of all female apheresis PLT donors, all female apheresis PLT donors with histories of prior pregnancies, or all female apheresis PLT donors with histories of prior pregnancies and positive screening test results for antibodies to human leukocyte antigens (HLAs) will result in a loss of 37.1, 22.5, and 5.4% of all apheresis PLT donations, respectively.A TRALI mitigation policy that only defers female apheresis PLT donors with previous pregnancies and HLAs would result in an approximately 5% decrease in the inventory of apheresis PLTs, but would eliminate a large proportion of components that are associated with TRALI.

Whole blood donation in the United States is restricted in volume to 10.5 mL/kg or less in an effort to prevent hypovolemic reactions, but still may exceed more than 15% of a donor's estimated blood volume (EBV). We analyzed the association of EBV with prefaint and systemic vasovagal reactions (SVRs) among whole blood donors and the potential impact of an EBV-based deferral policy.Independent predictors for prefaint reactions and SVRs were assessed by multivariate logistic regression analysis on 591,177 unique donors participating in the Retrovirus Epidemiology Donor Study-II study.Young age (16 years old odds ratio [OR], 3.70; 95% confidence interval [CI], 2.78-4.94), low EBV (3.5 L OR, 3.30; 95% CI, 2.57-4.23), and first-time donation status (OR, 2.33; 95% CI, 2.03-2.67) were the strongest predictors for SVRs, with similar trends seen for prefaint reactions. Sex, height, race, blood center, and donation site were weakly associated predictors. A total of 5.6% of all donors had an EBV of less than 3.5 L and experienced 12.5% of all prefaint reactions and 14.5% of SVRs. The highest reaction rates were seen in donors less than 23 years old with an EBV of less than 3.5 L who comprised 2.7% of all donors, who were mostly female (99.9%), and who experienced 8.8% of prefaint reactions and 11.0% of SVRs.Young age, low EBV, and first-time donation status are the major correlates of prefaint reactions and SVRs, suggesting that high school and college donors are at particular risk. Deferral of donors with low EBV who are less than 23 years old may offer a rational approach to protecting donors at greater risk of reactions without jeopardizing the adequacy of the blood supply.

Blood safety is a global public health priority. However, the degree to which blood is, or is not free of infection risk varies greatly around the world. The major determinants of this variation in risk are the availability of resources to support blood safety measures such as testing and the qualitative and quantitative epidemiological patterns of blood-borne infections. These factors are outlined and examples are presented.

In 1986, the FDA recommended using a confidential unit exclusion (CUE) option in blood centers; this was rescinded in 1992. The American Red Cross (ARC) has continued using the option. This study assessed its current impact.Donor records from ARC for 1995 through 2001 were examined for CUE use in association with the prevalence and frequency of seroconversion of infectious disease markers. The likely yield of CUE was also estimated.Donations with CUE use had a higher prevalence of HIV, HBV, HCV, and syphilis markers than those without CUE use, although both the sensitivity and positive predictive value (PPV) of CUE were low. Seroconverters had a higher frequency of using the CUE option than nonseroconverters. Similarly, the sensitivity and PPV of CUE were low. Based on analysis of infectious disease residual risk, the CUE option was estimated to have prevented the collection of 0.2 to 1.3 window-period units annually within the entire ARC system.The CUE option had minimal effectiveness in further reducing the transmission of infectious diseases through window-period units. Further study of its current impact on reduction of units from risky but test-negative donors, as well as on loss of safe donors, may be warranted.

In 1999, NAT of blood donations was implemented to detect "window-period" infections. Blood donors who have confirmed NAT results positive for the presence of HCV in the absence of anti-HCV are likely to have been recently infected. Of over 26.8 million donations tested between March 3, 1999, and March 31, 2003, 810 were HCV-reactive by NAT. A subset of these donors was assessed for recent exposure risk.All anti-HCV- blood donors with reactive, unconfirmed HCV NAT results were invited to participate in a study that included an extensive demographic and risk questionnaire. Confirmed HCV+ cases were compared to HCV- (falsely positive) controls for histories of potential risk factors during the 6 months before donation.Recent injection drug use (IDU) was independently associated with HCV infection (29.2% vs. 0% of cases vs. controls, p0.001). In addition, likely sources were identified for three other cases (4.6%), including occupational exposure, sexual contact with an HCV-infected partner (who was an IDU), and perinatal exposure, none of which was known to the donors at the time of donation. Incarceration was independently associated with HCV infection among the group not reporting IDU and after removal of the three donors with likely sources of risk (14.6% vs. 1.3% of cases vs. controls, p0.001).A likely risk, primarily IDU, was found for 43 percent of HCV+ donors whose infections were identified solely by NAT. Because the maximum efficiency of the donor history questions may have been reached, NAT will continue to be an important measure to interdict recently infected blood donors.

Although most attention has been paid to viral infections as a complication of transfusion, some parasitic infections are readily transmissible and generate a heavy burden of disease, particularly in the developing world. Additionally, bacterial infection as a result of transfusion is the most frequent serious outcome of transfusion in the developed world.Review of current literature and ongoing research studies.Malaria and Chagas' disease continue to be a serious problem in endemic areas, but are also of concern as a result of their introduction into other regions. Means to control or detect bacterial contamination, particularly of platelet concentrates, are needed, but no simple, effective approach is available.Continued development and implementation of tests and of inactivation procedures will result in the eventual control of transfusion-transmitted parasitic and bacterial disease.

Blood donors represent a carefully selected population of individuals. In particular, they have reduced prevalence and incidence rates for hepatitis and retroviral markers when compared to the general population. Serological testing of all donations further decreases the risk of collecting an infectious blood unit to negligible levels. Nevertheless, a significant fraction of this residual risk will be eliminated by the introduction of nucleic acid testing for viral genomic material in donor samples. This testing, which has already reached the initial phases of implementation, will be performed on pooled samples, at least in the first instance.

Since 1985 the theoretical risk of HIV infection posed by medical treatment with blood products has been very low. There have been no known cases of HIV transmission via blood products in Australia since that time. Nevertheless, blood banks continue to examine new techniques for reducing the risks.

Although intravenous immune globulin (IVIG) preparations may be derived from tens of thousands of donations, the residual risk of viral contamination of recovered plasma appears remarkably low, at least for human immunodeficiency virus (HIV) and hepatitis B virus (HBV). Consequently, most pools are unlikely to contain these viruses although the situation is not as well understood for US-derived source plasma. In addition, routine preparation methods are likely to eliminate infectivity from the relatively fragile HIV. Current plasma screening measures are generally designed to maintain reasonable titres of anti-HBs in pools, perhaps contributing to the absence of HBV infection. The situation with respect to hepatitis C virus (HCV) is not well understood and it appears that sensitive screening for anti-HCV may have had an impact on the safety of at least one IVIG preparation. The implementation of effective viral inactivation procedures is expected to eliminate any further risk of HCV infection from IVIG preparations.

Three population groups, 1500 blood donors, 513 antenatal women representing a normal population group and 250 sicklers representing a multiply transfused group were studied to determine the prevalence of hepatitis C viral (HCV) infection in Jamaica. The relationship to liver enzyme levels, hepatitis B infection, syphilis and HIV infection was also investigated. Sera were screened by enzyme-linked immunoassay (EIA) for anti-HCV C100-3 and subsequently tested by a supplementary second generation recombinant immunoblot assay (RIBA). In the blood donors, the prevalence of anti-HCV was low, 0.3%-0.4%, the same level as that reported by several European countries. In the multiply transfused sicklers, the prevalence was more than seven times higher. No HCV infection was detected in the antenatal group. There was little correlation between HCV infection and surrogate markers alanine aminotransferase (ALT) and antibody to hepatitis B core antigen (anti-HBc) and no correlation with sexually transmitted diseases.

For many years, viral hepatitis has been considered to be a frequent and serious adverse outcome of blood transfusion. The majority of cases have been due to hepatitis B and C viruses, which, respectively, are DNA and RNA viruses. Both are lipid enveloped and are susceptible to viral inactivation procedures. Careful donor screening and the use tests for HBsAg and anti-HBc have essentially eliminated the risk of transfusion-transmitted HBV infection.

Since the implementation of sensitive screening tests for hepatitis B virus infection, the majority of post-transfusion hepatitis has been due to infection with hepatitis C virus (HCV). The recent introduction of tests for antibodies to this virus has demonstrably reduced the incidence of post-transfusion HCV infection. There is some residual post-transfusion and sporadic hepatitis, which may possibly be caused by an as yet undescribed aetiologic agent. However, evidence for or against such an agent is by no means definitive. The majority of cases of this residual hepatitis seem to be mild and progression to chronicity is less frequent than for HCV infection. There is no evidence to suggest that modern, fully inactivated pooled plasma products transmit this poorly characterized form of hepatitis. However, in some circumstances, the potential for transmission of non-enveloped viruses by clotting factors may persist.

Despite the low risk of transfusion-transmitted infection currently present in the blood supply, processes to inactivate contaminating viruses and bacteria may improve the safety of transfusion even further. A variety of techniques, using both physical and chemical processes, are being explored. Particularly promising is adaptation of the solvent/detergent technique (already in use for plasma derivatives) to plasma for transfusion. Inactivation of viruses in cellular components may require a combination of techniques, possibly including leukocyte depletion filtration, photoactive compounds, and subsequent washing. Concerns about potential toxicity of the agents employed and retention of component efficacy after treatment and storage remain unresolved, however.

A wide variety of viruses are inactivated by psoralen compounds in the presence of ultraviolet A light (UVA). Use of aminomethyltrimethylpsoralen (AMT) and UVA is being evaluated as a method to inactivate viruses that may be present in platelet suspensions prepared for transfusion. Studies have been conducted to assess how variation in various environmental parameters influences the extent of viral inactivation and the retention of platelet properties. Most notably, it was determined that increasing levels of plasma progressively inhibited the inactivation of model viruses. As a result, experiments were routinely conducted at a plasma level of approximately 14.5%, using 40 micrograms/ml AMT, which was determined to be optimal when using this reduced plasma level. The reduced plasma level was achieved by dilution with a nonplasma medium that has been shown to be satisfactory for storage of platelets. Under these conditions, about 5 logs of vesicular stomatitis virus (VSV), pseudorabies, and phi 6 inactivation were achieved. Variation of platelet and leukocyte counts, within normal levels, had a minimal effect on extent of viral inactivation. Although oxygen level (mean levels, 97.9 mm Hg versus 19.2 mm Hg) had only a small influence on viral inactivation with 2.4, 4.8, and 7.2 J/cm2 of UVA (equivalent to 1-3 minutes of exposure), in vitro platelet properties, such as medium pH, morphology characteristics, and aggregation response, were better retained with a longer exposure time at the reduced oxygen level. With normal oxygen (97.9 mm Hg), platelet properties declined substantially relative to untreated controls (no UVA, no AMT) on exposure to 4.8 J/cm2. Our studies have identified two sets of conditions that provide about 5 logs of virus inactivation without extensively altering platelet in vitro properties.

Interpretation of human immunodeficiency virus (HIV) antibody results that are "indeterminate" rather than clearly positive or negative is problematic for the person delivering the result as well as for the individual being tested. To improve counseling messages for these individuals, we evaluated data collected from a well-characterized cohort of 387 blood donors who had been monitored for up to 2 years. We sought to determine if persons with indeterminate Western blot patterns were infected with HIV, and whether information derived from follow-up monitoring would assist in the development of counseling messages for persons on whom no follow-up information was available. Donors were studied by laboratory assays, clinical evaluation, and assessment of risk for HIV. The absence of HIV infection in 97 of 98 donors with indeterminate Western blot patterns was confirmed by clinical follow-up, Western blot assays of sequential samples, and negative gene amplification results. We propose supplemental guidelines to be used as an adjunct to existing interpretive criteria for counseling individuals when they first present with an indeterminate Western blot finding.

Natural history studies conducted over the past 15 years have shown that parenterally transmitted non-A non-B hepatitis infection frequently results in an indolent chronic disease with serious long-term consequences. The recent identification of nucleic acid sequences comprising the genome of hepatitis C virus (HCV) has allowed the development of a serological assay based upon recombinant viral proteins specifically associated with the major agent of non-A, non-B hepatitis infection. The HCV antibody assays have now been applied to sera from blood donors worldwide, as well as various population samples with increased hepatitis risk in the course of clinical trials conducted in both Europe and the United States. Data from these studies provide further encouragement that assays based on the hepatitis C virus recombinant proteins are highly specific for the major agent of non-A non-B hepatitis and will provide a firm basis for blood donor screening and future diagnostic tests.

The Western blot is frequently used to confirm human immunodeficiency virus type 1 (HIV-1) screening tests as it permits the identification of antibodies to individual component polypeptides of HIV-1. The procedure is described and different criteria for evaluation of HIV-1 Western blots are compared. The significance and management of indeterminate blot patterns are discussed.

Aliquots of a serum preparation called "run control" containing low levels (1.4 ng/ml) of hepatitis B surface antigen (HBsAg) were tested by four American Red Cross Blood Services regions using a commercial test based on enzyme-linked immunosorbent assay (EIA). The run control was tested a total of 424 and 892 times by procedures A and C, respectively, as recommended by the manufacturer (Abbott Laboratories, North Chicago, IL) of the EIA test kit. Results of all the tests were analyzed and showed that the run control was stable and reliable under field conditions. Illustrative examples of different approaches for the use of the run control in monitoring quality control of HBsAg testing are discussed.

Sixteen patients who received Konyne for bleeding episodes or for hemostasis during surgical procedures were evaluated for signs of posttransfusion hepatitis. Four patients died from their primary disease. Of the remaining 12 patients at risk, six patients developed posttransfusion hepatitis. Sera from four of the six patients with hepatitis were positive for the hepatitis B antigen (HBAg). Aliquots of Konyne from the specific lot (K4797) implicated in three cases of HBAg-positive hepatitis were negative for HBAg by immunodiffusion, immunoelectroosmophoresis, and radioimmunoassay. The high incidence of hepatitis associated with Konyne considerably limits the use for this specialized coagulation factor concentrate. HBAg screening by available technics does not necessarily detect Konyne preparations capable of transmitting HBAg-positive hepatitis.

In this study the authors examine the effects of common storage and handling procedures on serum alanine aminotransferase (ALT) levels. Clotted blood samples from 14 subjects were centrifuged at 280 X g for 10 minutes. Serum was tested immediately for baseline ALT levels and aliquots were stored at 22, 4, -20, and -80 degrees C. Additional serums were stored on the clot at 22 and 4 degrees C. ALT quantitation was performed at intervals of 3, 6, 9, and 24 hours and on Days 2, 4, 6, and 8. Unseparated tubes were sampled both proximal and distal to the red cells to determine ALT leakage from red cells lysis. For all storage conditions, gradual loss of activity occurred over time. Mean activity loss in separated serum at 2 days was 6 percent at 4 degrees C and 20 percent at 22 degrees C. Mean loss in unseparated serum was 3 percent at 4 degrees C and 12 percent at 22 degrees C. Marked ALT loss averaging 46 percent by day 6 occurred with storage at -20 degrees C, whereas storage at -80 degrees C resulted in an 8 percent decrease for the same period. For storage of up to 1 week, it is recommended that serum be separated early and retained at 4 degrees C. Frozen samples should be kept at -80 degrees C. Storage of separated or unseparated blood for up to 24 hours at 22 or 4 degrees C, as commonly found in blood centers, will marginally adversely affect the accuracy of ALT determination.

The present study was undertaken to determine whether there were any differences in the distribution of hepatitis B virus-(HBV) associated serologic markers among hepatitis B surface antigen-(HBsAg) positive first-time and repeat blood donors. The markers examined in samples from 412 newly identified HBsAg-positive donors (254 first-time and 158 repeat) included HBsAg titer and subtype, HBeAg/anti-HBe, and anti-HBc. Repeat donors were more frequently HBeAg-positive (25.9%) than were first-time donors (17.7%). Anti-HBc and anti-HBe were observed more often among first-time (99.6 and 76%) than repeat (91.8 and 60.8%) donors. No differences were found in the mean HBsAg titer nor in the subtype distribution in the two populations. The frequency of HBeAg positivity and the mean HBsAg titer in blood were significantly lower among first-time donors aged 30 or older as compared to those younger than 30. Such age-related tendencies did not occur among the repeat donors. The profiles of HBV makers suggest that the HBsAg-positive first-time donor group consists predominantly of long-term HBsAg carriers who may have acquired HBV at an early age, while the HBsAg-positive repeat donors have newly acquired infections.

Blood samples from 98 asymptomatic volunteer blood donors, including 55 that were reactive for antibodies to human immunodeficiency virus (HIV) in Western blot (WB) assay, were tested for levels of immunoglobulin G (IgG), IgM, and titer of antibodies to HIV, cytomegalovirus, and herpes simplex virus. Levels of IgG were significantly elevated (P less than or equal to 0.001) in donors with specific anti-HIV reactivity. A total of 69% of donors with anti-HIV had IgG levels of greater than or equal to 12 mg/ml, and 44% had IgG levels of greater than or equal to 14.5 mg/ml. Levels of IgM were not significantly different among WB-reactive and nonreactive donors. The titer of anti-HIV was significantly (P less than 0.02) correlated with IgG levels among donors reactive in the WB assay. Elevation of IgG, however, was not significantly associated with the presence of anticytomegalovirus or anti-herpes simplex virus antibodies. The data show that elevation of IgG may represent an early manifestation of HIV infection before the development of clinical symptoms of acquired immunodeficiency syndrome.

Eight percent of blood donors were found to have antibodies to hepatitis B surface antigen when tested by radioimmunoassay using commercial test kits. Four percent of positive reactions proved nonspecific when tested by the neutralization test using pooled surface antigen. The risks in relying solely on the reactivity in commercial-kit suggested that the specificity of the assay must be confirmed.

A total of 20,643 samples of blood donated to three American Red Cross Blood Service regions were tested for antibodies to hepatitis B core antigen (anti-HBc) in order to evaluate and understand its significance and implications. All 20,643 samples were non-reactive for hepatitis B surface antigen (HBsAg) when screened at the regions. Overall, 2.2% of all samples were found to have anti-HBc, and a total of 16 had anti-HBc in the absence of antibodies to surface antigen (anti-HBs) activity. 1 of the 16 samples with anti-HBc in the absence of anti-HBs was found to have HBsAg when tested by a sensitive procedural modification of the Austria II test. Samples with low levels of anti-HBc activity were significantly more likely to be negative for anti-HBs.

From January 1975 to December 1978, 19,140,169 units of blood were collected by the American Red Cross at 57 regional locations. Each unit was tested for hepatitis B surface antigen (HBsAg) by a single commercial radioimmunoassay test system. A total of 15,954 donations were reported reactive, representing a rate of HBsAg reactivity of 0.83/1,000 units tested. The rate during 1975 was 0.94/1,000 units tested, decreasing to 0.71/1,000 units tested in 1978 (p0.005). The prevalence of HBsAg among first-time donors was 2.08/1,000 during 1977 and 1978, 2.7 times higher than that calculated for repeat donors (0.77/1,000 donors). Substantial geographic variation in the prevalence and rate of detection of HBsAg was observed.

The safety of blood and blood products is based on three interdependent activities: selection of safe donors, laboratory testing, and, where applicable, treatment of the product to reduce residual infectivity. Posttransfusion hepatitis has provided both the initial stimulus and the model for these procedures. The procedures have resulted in a progressive increase in the safety of the blood supply, which is continuing, as evidenced by a 50% decrease in the frequency of reported posttransfusion hepatitis over the past two years.

The results of hepatitis B surface antigen (HBs-Ag) testing in a large volunteer blood donor population are described. Counterelectrophoresis and three versions of solid-phase radioimmunoassay technic are compared and evaluated. Initial results suggested that the radioimmunoassay technic are compared and evaluated. Initial results suggested that the radioimmunoassay technic detected more than five times as many reactive donors as did counterelectrophoresis. The specificity of the radioimmunoassay technic has been increased by successive modifications, and recent results show that the technic detects 73 percent more reactive donors than does counterelectrophoresis. Not all of these reactions are specific, and it is estimated that the true gain in detection of HBsAg carriers is 49 percent of the value found by counterelectroesis. The incidence of HBsAg carriers in the America Red Cross donor population is about 1.25 per 1,000.

During the year 1978 this laboratory evaluated the specificity of all samples found reactive for hepatitis B surface antigen (HBsAg) by 44 of 57 regions of the American Red Cross Blood Services. Radioimmunoassay detected a total of 1.921 HBsAg-reactive sampled among more than three million donor units tested. A vast majority (96%) of the samples had high level of HBsAg (greater than or equal to 20 ng/ml). Only about 50% of the samples with low level of HBsAg (less than 20 ng/ml) were reactive in reversed passive hemagglutination. There were 13 samples that were repeatable for HBsAg but were considered nonspecific as they were nonneutralizable in radioimmunoassay, 2 donors who showed nonspecific reactivity were further tested and it was found that the reactivity in radioimmunoassay persisted for more than 9 months, and this reactivity was also detectable by a second commercial kit for HBsAg. Antibodies to core and surface antigen were not found in any of the nine samples that were tested. The explanation of this nonspecific reactivity is unclear, but the data suggest that the nonspecific factor(s) may be an inherent property of the sample rather than a deficiency of the test reagents.

Hepatitis B surface antigen (HBsAg) may be insolu-bilized onto a controlled pore glass (CPG) matrix by simple adsorption from acidified serum or plasma. The resultant complex has the properties of an HBsAg-specific immunoadsorbent. In this study, CPG-HBsAg complexes have been used to adsorb anti-HBs from standard immune serum globulin. Specific antibodies were eluted with acidic or chaotropic buffers. Recoveries ranging from 29 to 46 per cent, with purifications of approximately 1000-fold were obtained. Two procedures designed to inactivate hepatitis B virus had no effect upon the immunoadsorbent properties of the CPG-HBsAg complex. The possibility of using this simple method to prepare hepatitis B immune globulin is discussed.

The Stokes radius of umpurified hepatitis B antigen (HBSAg) was determined by chromatography on a carefully calibrated Sepharose 4B column. A value of 14-2 nm was found by this procedure, contrasting with a published value of II nm for purified, pepsin-treated HBSAg. Chromatography at pH 3 appeared to reduce the Strokes radius of HBSAg to II nm. Evidence is presented to show that serum proteins adsorbed to HBSAg can be removed with pepsin or acid.

A robotic handling system was adapted to perform the sampling and dilution steps needed in an assay to detect antibodies to the HTLV-III virus, the causative agent of AIDS. The system reduced the labor required to prepare the samples and provided standardization and accuracy in the preparation of the samples.

The American Red Cross collects blood from a number of defined subsets of the donor population and teh proportion of blood collected from each subset varies widely from center to center. A large part of the variation in prevalence of HBsAg may be related to variations in the proportion of blood collected from plants and factories, military units and schools or colleges. We have derived a regression equation, significant at the p less than 0.001 level, which links HBsAg prevalence with these collection parameters. Using this equation, we were able to predict the prevelance of HBsAg among first-time donors in 6 of the 9 geographic divisions of the United States with an accuracy exceeding 10%. The predictions for the remaining division were within 35% of the actual value. Correlation studies were supported by measurements of true donor prevalence in three blood centers.

Radioactive cores were prepared from concentrated Dane particles by DNA polymerase reaction followed by CsCl density gradient centrifugation. Two radioactive peaks were obtained: one peak with an average density of 1.36 g/cm-3 in CsCl contained cores that possessed full serologic reactivity; the other peak, with a density of 1.28 to 1.32 g/cm-3, contained cores associated with globulin. A double antibody immunoprecipitation test was developed, using the radioactive heavy cores as a source of antigen. The test was at least 300 times as sensitive as complement fixation for detecting antibody to core.