Leukocyte reduction's role in the attenuation of infection risks among transfusion recipients.

Despite advances in the screening of donated blood for infectious agents, the risk of transmitting viral, bacterial, and protozoal infections, as well as newly emerging diseases, via transfusion persists. A complementary approach is leukocyte reduction (LR), the removal of leukocytes from donated blood by filtration. Published evidence, establishing the benefit of LR in reducing the risk of febrile nonhemolytic reactions, cytomegalovirus transmission, and human leukocyte antigen alloimmunization has led to its use for some time for the care of immunosuppressed and other individuals considered to be at high risk for such complications. Recent literature suggests that LR may be effective in reducing the risk of transmission of a number of additional transfusion-transmitted infectious agents, including herpesviruses, retroviruses, bacteria, protozoa, and prions. There is also evidence that LR may reduce the risk of transfusion-related immunomodulation, further contributing to protection against infections that would complicate treatment. With the mounting evidence of potential benefit, a number of countries, as well as many hospitals and blood centers in the United States, have adopted a policy of performing LR for all donated blood. Physicians who care for immunosuppressed patients and those who are responsible for institutional infection-control practices should remain informed of the growing body of literature on LR.

An overview of prion biology and the role of blood filtration in reducing the risk of transfusion-transmitted variant Creutzfeldt-Jakob disease.

Prions are infectious proteins believed to be responsible for a variety of progressive and fatal neurodegenerative diseases, collectively referred to as transmissible spongiform encephalopathies (TSE). By 1996, it was recognized that ingestion of beef from cattle afflicted with a TSE known as bovine spongiform encephalopathy, could result in a devastating human TSE known as variant Creutzfeldt-Jakob disease (vCJD). Two recent reports of probable transfusion-transmitted vCJD have raised concerns about the safety of the blood supply. The relatively long asymptomatic latency of vCJD, as well as the lack of sensitive and specific antemortem tests, increase the risk that asymptomatic, infected individuals may become blood donors. To this point, donor deferral has been a strategy used to reduce this risk. Nevertheless, this strategy may be unreliable and, furthermore, may threaten blood availability. Leukoreduction has also been helpful in reducing cell-associated infectious prion, which has been reported to reduce up to 42% of the infectivity in blood. Proprietary prion affinity surface modifications have been developed and applied to filters, which exploit an understanding of the unique chemical characteristics of prion surfaces. These have been successfully adapted to existing high-efficiency blood filter matrices for the reduction of prions present in blood components for transfusion.

Hospital water point-of-use filtration: a complementary strategy to reduce the risk of nosocomial infection.

Cholera, hepatitis and typhoid are well-recognized water-borne illnesses that take the lives of many every year in areas of uncontrollable flood, but far less attention is afforded to the allegedly safe potable water in affluent nations and the presumed healthful quality of water in communities and hospitals. Recent literature, however, points to increasing awareness of serious clinical sequelae particularly experienced by immunocompromised patients at high risk for disease and death from exposure to water-borne microbes in hospitals. This review reflects the literature indicting hospital water as an important source for nosocomial infections, examines patient populations at greatest risk, uncovers examples of failures in remedial water treatment methods and the reasons for them, and introduces point-of-use water filtration as a practical alternative or complementary component of an infection control strategy that may reduce the risk of nosocomial infections.

Universal leukocyte reduction: Is it appropriate medical practice or not?

This article discusses the evidence for the generally accepted uses of leukocyte-reduced blood and the controversy over leukocyte reduction and transfusion-related immunomodulation. A perspective is provided on the continued need for leukocyte reduction on the part of all patients in the United States.

Prion biology in transfusion medicine: implications for lab testing.

Although eerily silent for many years after the recognition of scrapie in 1759, TSEs remained present within the genome of some mammals. Not since the mid-1950s when Dr. Carleton Gadjusek visited the Fore Indians of New Guinea to study kuru, however, has there been a more frenetic interest by governmental investigators. Certainly, the U.K. experience has heralded a renewed interest in TSEs due to the notoriety associated with younger subjects succumbing to a variant CJD traced to the ingestion of beef. Human TSEs and the potential for their transmission among and across species of mammals has also captured the attention of many. Yet, to date, there is no reliable antemortem test available to screen for infected animals or humans. Antibody-based assays are difficult to develop because most of them do not have specificity for the pathogenic form of prion protein. Whether or not prion testing efforts will change dramatically depends upon the incidence of disease. Some speculate a reduction in testing, because BSE incidence is waning since the adoption of remedial steps in the U.K. in 1989. Others remind us, however, of the long latency of prion diseases and of the recent observations of two patients who succumbed to vCJD after having received blood products from donors who subsequently died of vCJD. The growing incidence of CWD, combined with the emerging observation that as many as 26% of Alzheimer's patients may have been misdiagnosed--having died instead of prion disease--maintains pressure for legislators to adhere to the precautionary principle and support blood-donor exclusionary criteria, antemortem-test development, and pathogen removal from donated blood. The laboratorian can expect to see new tests for prion disease work their way into clinical-testing practice in the near future. In addition, the adoption of newer filtration technologies holds the promise of improved protection from transfusion-transmitted prion disease.

A brief history of blood filtration: clot screens, microaggregate removal, and leukocyte reduction.

A historical perspective of the evolution of blood filtration is presented. Topics addressed include recognition of aggregates in blood as mediators of morbidity, targeted for removal with gross clot screens, and evolution through the implementation of universal leukocyte reduction. Future directions for the development of blood filters are also described.

Sensitive fluorescent detection of protein on nylon membranes.

Detection of antigen immobilized on membranes, as in Western transfers and dot enzyme linked immunosorbent assays (ELISAs), often employ antibody-enzyme conjugates and chemiluminescent or precipitated colored reaction products. Although chemiluminescent markers are sensitive, they are time-consuming because of their required exposure to X-ray film and the presence of background artifacts sometimes limits their use. This report demonstrates that direct fluorescent detection technique using nylon membranes that has higher sensitivity than chemiluminescent methods is easier to perform and has a uniform, low background. An alkaline phosphatase conjugated antibody was compared with antibody conjugated to a fluorescent phycobiliprotein (allophycocyanin) for sensitivity in both Western transfers and dot ELISA assays using mouse IgG as the membrane-bound antigen. Direct fluorescent detection of antigen-antibody complexes on positively charged nylon membrane provided better sensitivity and lower background than similar conditions using enzyme amplification and chemiluminescent detection on either nylon or PVDF membranes. Processing time was reduced by the elimination of steps associated with substrate incubation, washing and X-ray film exposures required for chemiluminescence detection. These data support the view that direct fluorescent detection can represent a significant improvement in assay sensitivity and reduction in time compared with more traditional chemiluminescent detection techniques employed in the conduct of Western transfers and dot ELISA studies.

Contamination control in nursing with filtration: part 2: emerging rationale for bedside (final) filtration of prestorage leukocyte-reduced blood products.

The first part of this 2-part series focused on the manufacture of filters and the application of filtration technology to intravenous fluids and point-of-care hospital water. This second part describes an apparent emerging potential for final filtration defined as bedside filtration of blood and component blood products leukocyte-reduced at the blood center prior to storage. Final filtration serves to further reduce the leukocyte burden in a previously leukocyte-reduced blood product. Another target for final filtration includes putative soluble mediators of morbidity.Selected patients may be at greater risk for alloimmunization and refractory to the benefits afforded by transfusion of blood leukocyte reduced to the current established standards. Multiparous patients who subsequently find themselves in need of a transplanted organ are alloimmunized by exposure to fetal proteins and may be further alloimmunized by transfusion. Such effects can put them at risk for increased latency for donor organ availability and organ rejection. Kidney transplant patients find themselves the recipients of transfused blood products particularly during end-stage renal disease and recent data suggest such patients are not benefited by the levels of leukoreduction prescribed by current standards and may need more dramatic leukocyte removal. The process of blood production is described and affords a greater appreciation for the levels of white cells found in component blood products. The development of alloimmunization is reviewed and fosters greater appreciation for a discussion of the potential for therapeutic value of more dramatic leukocyte reduction and blood conditioning accomplished through the removal of soluble mediators of morbidity.

Contamination control in nursing with filtration. Part 1: filters applied to intravenous fluids and point-of-use hospital water.

Filters often are viewed as screens with openings smaller than the particles intended to be removed by a process technically known as direct interception. However, filter manufacturing embraces far more advanced technological approaches, with an evolution toward selective removal of cells or soluble constituents from complex physiologic solutions. An appreciation of filtration development makes it easy to understand how differently manufactured filters with the same claims may not perform identically. This article focuses on the filtration of intravenous solutions and point-of-use hospital water.

A randomized controlled trial of the efficacy of autologous platelet therapy for the treatment of osteoarthritis in dogs.

OBJECTIVE: To determine efficacy of a single intra-articular injection of an autologous platelet concentrate for treatment of osteoarthritis in dogs. DESIGN: Randomized, controlled, 2-center clinical trial. ANIMALS: 20 client-owned dogs with osteoarthritis involving a single joint. PROCEDURES: Dogs were randomly assigned to a treatment or control group. In all dogs, severity of lameness and pain was scored by owners with the Hudson visual analog scale and the University of Pennsylvania Canine Brief Pain Inventory, respectively, and peak vertical force (PVF) was determined with a force platform. Dogs in the treatment group were then sedated, and a blood sample (55 mL) was obtained. Platelets were recovered by means of a point-of-use filter and injected intra-articularly within 30 minutes. Control dogs were sedated and given an intra-articular injection of saline (0.9% NaCl) solution. Assessments were repeated 12 weeks after injection of platelets or saline solution. RESULTS: Dogs weighed between 18.3 and 63.9 kg (40.3 and 140.6 lb) and ranged from 1.5 to 8 years old. For control dogs, lameness scores, pain scores, and PVF at week 12 were not significantly different from pretreatment values. In contrast, for dogs that received platelet injections, lameness scores (55% decrease in median score), pain scores (53% decrease in median score), and PVF (12% increase in mean PVF) were significantly improved after 12 weeks, compared with pretreatment values. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that a single intra-articular injection of autologous platelets resulted in significant improvements at 12 weeks in dogs with osteoarthritis involving a single joint.

Comparison of human bone marrow mononuclear cell isolation methods for creating tissue-engineered vascular grafts: novel filter system versus traditional density centrifugation method.

INTRODUCTION: We created the first tissue-engineered vascular graft (TEVG) to be successfully used in humans. The TEVG is made by seeding autologous bone marrow-derived mononuclear cells (BM-MNCs) onto a biodegradable tubular scaffold fabricated from polyglycolic-acid mesh coated with a 50:50 copolymer of poly-L-lactide and-ɛ-caprolactone. In the initial clinical study, the BM-MNCs were isolated using a Ficoll density centrifugation method. Use of this cell isolation technique is problematic in that it is performed using an open system and therefore is susceptible to contamination. As a first step toward creating a closed system for assembling a TEVG, we evaluated the use of a filter-based method for isolating BM-MNCs and compared it to density centrifugation in Ficoll. METHODS: BM-MNCs were isolated from human BM using density centrifugation in Ficoll or a filter-based method. BM-MNCs were seeded onto biodegradable tubular scaffold and incubated for 24 h before implantation. The TEVG were implanted as inferior vena cava interposition grafts in SCID/bg mice (n=24) using microsurgical technique. Grafts were followed with ultrasonography and computed tomography-angiography. Ten weeks after implantation the TEVG were explanted and examined using histology and immunohistochemistry. RESULTS: Both methods isolated similar number of cells (Ficoll: 8.5±6.6×10(6)/mL, Filter: 6.6±3.5×10(6)/mL; p=0.686) with similar viability as assayed using fluorescence-activated cell sorting (FACS) (Ficoll: 97.0%±1.5%, Filter: 95.9%±3.0%; p=0.339). FACS analysis demonstrated that the fraction of lymphocytes and monocytes to total cells was lower in the filter group (CD4 in Ficoll: 8.9%±1.1%, CD4 in Filter: 3.5%±0.8%; p=0.002, CD8 in Ficoll: 9.4%±2.1%, CD8 in Filter: 3.9%±1.4%; p=0.021, Monocyte in Ficoll: 6.9%±1.0%, Monocyte in Filter: 2.7%±1.0%; p=0.008), consistent with granulocyte contamination (Ficoll: 46.6±2.7×10(6)/mL, Filter: 58.1±5.2×10(6)/mL; p<0.001). The ratio of stem cells to BM-MNCs was comparable between groups. There were no statistically significant differences with regard to TEVG patency and morphology between groups. Both methods of cell isolation produced neovessels with similar histology. CONCLUSION: Filter-based BM-MNC isolation is comparable to BM-MNC isolation using density centrifugation in Ficoll for TEVG assembly. The filter-based cell isolation technique has the added advantage of the potential to create a closed disposable system.

Preventive efficacy and cost-effectiveness of point-of-use water filtration in a subacute care unit.

Infections with Pseudomonas aeruginosa and other waterborne pathogens (WBPs) are major contributors to serious morbidity and mortality in hospitals. We sought to determine whether point-of-use (POU) water filtration might result in decreased risk of infection in the subacute care unit (SACU) of a 208-bed medical center. Our findings indicate that POU water filtration can significantly and cost-effectively reduce colonization of and infection with WBPs, including ventilator-associated pneumonia, in an SACU.

Reperfusion injury following cerebral ischemia: pathophysiology, MR imaging, and potential therapies.

INTRODUCTION: Restoration of blood flow following ischemic stroke can be achieved by means of thrombolysis or mechanical recanalization. However, for some patients, reperfusion may exacerbate the injury initially caused by ischemia, producing a so-called "cerebral reperfusion injury". Multiple pathological processes are involved in this injury, including leukocyte infiltration, platelet and complement activation, postischemic hyperperfusion, and breakdown of the blood-brain barrier. METHODS/RESULTS AND CONCLUSIONS: Magnetic resonance imaging (MRI) can provide extensive information on this process of injury, and may have a role in the future in stratifying patients' risk for reperfusion injury following recanalization. Moreover, different MRI modalities can be used to investigate the various mechanisms of reperfusion injury. Antileukocyte antibodies, brain cooling and conditioned blood reperfusion are potential therapeutic strategies for lessening or eliminating reperfusion injury, and interventionalists may play a role in the future in using some of these therapies in combination with thrombolysis or embolectomy. The present review summarizes the mechanisms of reperfusion injury and focuses on the way each of those mechanisms can be evaluated by different MRI modalities. The potential therapeutic strategies are also discussed.

Filters reduce the risk of bacterial transmission from contaminated heated humidifiers used with CPAP for obstructive sleep apnea.

RATIONALE: The treatment of choice for obstructive sleep apnea (OSA) is nasal continuous positive airway pressure (nCPAP) during sleep, but dryness of the upper airway compromises compliance. Heated humidifiers may mitigate such noncompliance; however, recent observations suggest that their use, particularly if not cleaned, increases the risk of respiratory infections. Humidifier water may be contaminated, but the long-held view that passive humidifiers cannot aerosolize water may obscure the perception of risk of infection. OBJECTIVES: This study challenges the long-held view that "passover" humidifiers do not aerosolize water. With such evidence, this study characterizes the performance of filters to reduce the potential risk of contamination. METHODS: Heated humidifier water contaminated with bacteria was studied under conditions simulating week-long use of nCPAP for OSA. RESULTS: Bacteria were recovered in 9 of 11 tests from the breathing tubes of CPAP devices fitted with heated humidifiers with water contaminated with Brevundimonas diminuta or Serratia marcescens. Recoverable bacteria ranged from tens to thousands of colony forming units when tested at air flow rates of 60 liters per minute for 90 minutes. Neither organism was recovered from the circuit tubing when a hydrophobic breathing-circuit filter was positioned between the humidifier and face-mask tubing with a commercially available nCPAP machine tested under simulated-use conditions. CONCLUSION: Data suggest that patients with OSA being treated with nCPAP fitted with humidifiers may be aerosolizing bacteria, putting them at risk for developing respiratory infections and that the use of a hydrophobic filter may attenuate the passage of microbes from contaminated humidifier water.

Enhancement of a culture-based bacterial detection system (eBDS) for platelet products based on measurement of oxygen consumption.

BACKGROUND: An enhanced bacterial detection system (Pall eBDS) was developed that distinguishes itself from its predecessor (Pall BDS) by removal of the platelet (PLT)-retaining filter allowing for optimal bacterial transfer, modification of the culture tablet to reduce the confounding effects of respiring PLTs while enhancing bacterial growth, and facilitation of nutrients and gas exchange by agitating the sample pouch during incubation at 35 degrees C. The objective was to evaluate the performance of the new eBDS. STUDY DESIGN AND METHODS: Leukoreduced whole blood-derived PLT concentrates (LR-PCs) and LR single-donor PLTs (LR-SDPs) were inoculated with 1 to 15 colony-forming units (CFUs) of bacteria per mL in studies of each of 10 bacterial species associated with fatal transfusion-transmitted bacterial infection. Immediately after inoculation and after 24 hours of storage at 22 degrees C, samples of inoculated LR-PCs were aseptically transferred into the eBDS pouches. Pouches were then incubated for 24 hours at 35 degrees C with agitation and oxygen concentration was then measured. RESULTS: Median inoculation levels ranged from 5 to 13 CFUs per mL for each species studied. No significant differences in oxygen concentration were found when comparing LR-PCs with LR-SDPs. When sampling occurred from the PLTs 24 hours after inoculation, all 280 cases (24-33 replicates of each species) were detected as contaminated by the device (100% sensitivity). No false-positives were obtained with 713 uninoculated PLT units. CONCLUSIONS: The eBDS demonstrated improved detection sensitivity in the range of 1 to 15 CFUs per mL with no observed false-positives compared to the original BDS (detection range 100 to 500 CFUs/mL) with no false-positives.

A review of leukofiltration therapy for decreasing the morbidity associated with cardiopulmonary bypass and acute inflammatory bowel disease.

Complications of cardiopulmonary bypass (CPB) and acute inflammatory bowel disease (IBD) are associated with increased morbidity and cost. During reperfusion post-CPB, activated neutrophils adhere to microvascular endothelial cells mediated by cell adhesion molecules (CAMs) and cytokines/chemokines with subsequent myocardial damage caused by activated neutrophil-derived oxidants and enzymes. Leukofiltration was shown to reduce myocardial reperfusion injury and improve gas exchange as suggested by improvements in surrogate markers of inflammation and clinical end points. In acute IBD, characterized by rectal bleeding and protracted hospital stays, circulating neutrophils emigrate to the inflamed colon and adhere to microvascular endothelial cells by CAMs. Multiple treatments with leukofiltration in IBD were shown to induce long-term remission of acute IBD. Hence, leukofiltration may reduce reperfusion injury and rectal bleeding in CPB and IBD, respectively, and therefore decrease the morbidity and cost associated with these diseases.

Detection of bacteria in WBC-reduced PLT concentrates using percent oxygen as a marker for bacteria growth.

BACKGROUND: The risk of receiving a PLT concentrate (PC) contaminated with bacteria may be 1000-fold greater than that of pathogenic viral transmission, yet surveillance for this risk is not generally practiced. A novel bacteria detection system (BDS) that overcomes the limitations of current systems is described. The BDS monitors percent oxygen (%O2) in air above aliquots of PCs that have been filtered to remove the confounding effect of respiring PLTs and residual WBCs. STUDY DESIGN AND METHODS: One-day-old WBC-reduced whole-blood-derived PCs (WBPCs) were inoculated with bacteria at 100 to 500 CFU per mL. After 30 minutes, 2- to 3-mL aliquots were processed through a PLT-reducing filter into a sample pouch containing sodium polyanethol sulfonate and entrained air. After incubation at 35 degrees C for at least 24 hours, the %O2 was measured within the pouch. Noninoculated WBC-reduced WBPCs (n = 155), confirmed free of bacteria by routine culture, were tested in a like manner. Results from the latter group of WBC-reduced WBPCs were used to distinguish contaminated from noncontaminated units. RESULTS: After a 24-hour incubation at 35 degrees C, 195 (96.5%) of the 202 sample pouches obtained from inoculated units were detected by the BDS. After an additional 6 hours at room temperature, those that remained and were tested were found positive. None of the noninoculated controls produced a positive reading. CONCLUSION: The BDS is easy to use and provides good levels of sensitivity and specificity.

A review of leukofiltration in cardiac surgery: the time course of reperfusion injury may facilitate study design of anti-inflammatory effects.

The systemic inflammatory response syndrome (SIRS) is a well-recognized phenomenon attending cardiopulmonary bypass (CPB) surgery. SIRS leads to costly complications and several strategies intended to ameliorate the symptoms have been studied, including leukocyte reduction using filtration. Although the body of work suggests that leukoreduction attenuates SIRS, discrepancies remain within the literature. The recent literature is reviewed, highlighting the areas where concordance is lacking. Investigations into many promising device-related technologies are often deterred by the high costs of clinical trials. Adding to costs is the fact that clinical end points generally require large sample sizes. An understanding, however, of the pathogenesis of reperfusion injury can guide the investigator to choose physiologic response measures that correlate well with clinical outcome, but feature low inherent variability, allowing for clinical trials with smaller sample sizes. With this goal in mind, a model for the pathogenesis of reperfusion injury is described. Using a model of reperfusion injury as underpinnings for the design of prospective pilot studies, we show that salvaged blood reinfused following CPB elicits time-dependent effects on pulmonary function as predicted by the model. Data are illustrative of principles that could expand the scope of clinical investigations designed to validate the use of physiologic response measures as correlates of clinical outcome. Such investigations would target surrogate markers of clinical outcome, measured at clinically relevant times. Once validated, these surrogate markers would, thereafter, become economical screening tools for clinical studies of device-related or pharmacological anti- inflammatory interventions.