Paired Donations Research Articles

Relationship of Social Deprivation Among Living Kidney Donor–Recipient Pairs

Background. Living kidney transplant is the most effective renal replacement therapy for patients with end-stage kidney disease. Community-level factors contribute to pervasive socioeconomic and racial disparities in access to living donor kidney transplantation. Little is known about social and environmental conditions between living donors and recipients. Further understanding of these relationships may enhance opportunities for transplantation. Methods. From 2010 to 2020, 59 575 living kidney donor–recipient pairs (≥18 y old) were identified using the Scientific Registry of Transplant Recipients. Living donors and recipients were geocoded to area-level social deprivation index (SDI). The primary outcome was difference between recipient and donor SDI. We used multivariable logistic regression to examine recipient and donor characteristics association with residence in different SDI communities. Results. Living kidney donation occurs across all strata of social deprivation; including when donors, recipients or both reside in more disadvantaged communities. Donor–recipient race combination and biological relationship are associated with differences in SDI. When compared with White recipients of White donors, Black and Hispanic recipients were more likely to reside in more disadvantaged areas (odds ratio = 2.41 [2.19-2.66] and 1.97 [1.78-2.19]). Recipients in anonymous and paired donations were more likely to reside in areas of more disadvantage than their donors (odds ratio = 1.27 [1.15-1.40] and 1.32 [1.23-1.41] compared with biological); attenuating socioeconomic disparities in access to living donor transplantation. Conclusions. Findings illustrate the social and environmental relationships between living kidney donor–recipient pairs that are important to develop targeted approaches and address barriers to living kidney transplantation. Best practices from areas of high deprivation with successful living kidney transplantation can be shared.

Virtual crossmatch versus complement-dependent cytotoxicity crossmatch in deceased kidney paired donations: a single-center experience from India

Virtual crossmatch versus complement-dependent cytotoxicity crossmatch in deceased kidney paired donations: a single-center experience from India

P1730KIDNEY PAIRED DONATION IN SLOVAKIA - TOWARDS TO THE NATIONALLY COORDINATED PROGRAMME

Abstract Background and Aims AB0 and HLA incompatibility between donor and recipient is one of the possible reasons of the low rate of living kidney donation in Slovakia. Method We present a retrospective analysis of living donor kidney transplantations (LDKT) in Slovakia including kidney paired donations. Results During the period from 2015 to 2019 there were 823 kidney transplantations, 81 (9,8%) were from living donors. Kidney paired donations are performed since 2005. Altogether 8 two-way paired exchanges were done in 3 transplant centers. The first exchange between two centers was carried out in 2015. A majority of the involved pairs (81%) were married couples, one exchange was initiated by compatible pair. Surgical procedures were simultaneous, cold ischemia times were comparable to other LDKT (median 162 vs 182 minutes). Two recipients had early acute rejection, 3-year graft survival is 100%. There were no serious complications in donors. The participation in EU project ENCKEP (European Network for Collaboration on Kidney Exchange Programmes) has led to the creation of national registry of incompatible pairs in 2018 and the standardization of medical and legal processes of paired exchanges. Conclusion Above reported experience is adequate prerequisite for the launch of nationally coordinated programme and international cooperation.

Maximum matchings in graphs for allocating kidney paired donation

Living donors are often incompatible with their intended recipients. Kidney paired donation matches one patient and his or her incompatible donor with another pair in the same situation for an exchange. Let patient-donor pairs be the vertices of an undirected graph G, with edges connecting reciprocally compatible vertices. A matching in G is a feasible set of paired donations. Because the lifespan of a transplant depends on the immunologic concordance of donor and recipient, we weight the edges of G and seek a maximum edge-weight matching. Unfortunately, such matchings might not have the maximum cardinality; there is a risk of an unpredictable trade-off between quality and quantity of paired donations. We prove that the number of paired donations is within a multiplicative factor of the maximum possible donations, where the factor depends on the edge weighting. We propose an edge weighting of G which guarantees that every matching with maximum weight also has maximum cardinality, and also maximizes the number of transplants for an exceptional subset of recipients, while favoring immunologic concordance. We partially generalize this result to k-way exchange and chains, and we implement our weightings using a real patient dataset from Brazil.

Quantifying Donor Effects on Transplant Outcomes Using Kidney Pairs from Deceased Donors.

In kidney transplantation, the relative contribution of donor versus other factors on clinical outcomes is unknown. We sought to quantify overall donor effects on transplant outcomes for kidney donations from deceased donors. For paired donations from deceased donors resulting in transplants to different recipients, the magnitude of donor effects can be quantified by examining the excess of concordant outcomes within kidney pairs beyond chance concordance. Using data from the Organ Procurement and Transplantation Network between the years 2013 and 2017, we examined concordance measures for delayed graft function, death-censored 1-year graft failure, and death-censored 3-year graft failure. The concordance measures were excess relative risk, excess absolute risk, and the fixation index (where zero is no concordance and one is perfect concordance). We further examined concordance in strata of kidneys with similar values of the Kidney Donor Profile Index, a common metric of organ quality. If the transplant of the kidney mate resulted in delayed graft function, risk for delayed graft function was 19% higher (95% confidence interval [95% CI], 18% to 20%), or 1.76-fold higher (95% CI, 1.73- to 1.80-fold), than baseline. If a kidney graft failed within 1 year, then the kidney mate's risk of failure was 6% higher (95% CI, 4% to 9%), or 2.85-fold higher (95% CI, 2.25- to 3.48-fold), than baseline. For 3-year graft failure, the excess absolute risk was 7% (95% CI, 4% to 10%) but excess relative risk was smaller, 1.91-fold (95% CI, 1.56- to 2.28-fold). Fixation indices were 0.25 for delayed graft function (95% CI, 0.24 to 0.27), 0.07 for 1-year graft failure (95% CI, 0.04 to 0.09), and 0.07 for 3-year graft failure (95% CI, 0.04 to 0.10). Results were similar in strata of kidneys with a similar Kidney Donor Profile Index. Overall results indicated that the donor constitution has small or moderate effect on post-transplant clinical outcomes.

Evaluation of Whether Kidney Paired Donations Improve Overall Transplant Center Performance.

Increasing living-donor kidney transplant procedures via kidney paired donations could help combat organ shortages. We examined whether a higher volume of kidney paired donation transplants would lead to increased center performance. Kidney paired donation, living-donor, and deceased-donor transplant data from 165 centers between 2012 and 2016 were obtained from the UNOS OPTN database. The fixed-effects model was used for panel analysis based on Durbin-Wu-Hausman tests (P < .001). Regression analyses tested associations between total transplant number and kidney paired donation-to-living donor kidney transplant ratio, incorporating up to 2-year lag terms. Regression analyses also tested associations between number of new wait list registrations and kidney paired donation transplant ratio. Mean and median number of kidney paired donor transplants equaled 3.59 and 1.2, respectively. Only 5 centers performed > 20 paired donation transplants annually. Mean and median ratios of paired donation transplants were 0.54 and 0.11. Total transplant number was not associated with paired donation transplant ratio of the same year (b= -.425, P = .662) or with that of 2 prior years (P = .830 and P = .629, respectively). Similarly, new wait list registrations were not correlated with paired donation transplant ratio of the same year (P= .501, P = .851) or that of 2 prior years (P = .792 and P = .816, respectively). When transplant centers were divided into those performing ≥ 10 paired donation trans-plants annually (18 transplant center, n = 90) versus those performing < 10 annually (147 transplant center, n = 735), no significant effects were shown (P > .10). Kidney paired donation transplant does not appear to affect transplant center performance. This may be due to the small volume of these transplants currently performed by centers, thereby limiting overall growth in the number of transplants and new registrations.

Seventy-seven kidney paired donation transplantations at a single transplant centre in India led to an increase in living donor kidney transplantations in 2015.

BackgroundTo ascertain the validity of kidney paired donations (KPDs) as an alternative strategy for increasing living donor kidney transplantations (LDKTs) in an LDKT-dominated transplant programme since directed kidney transplantation, ABO-incompatible or crossmatch-positive pairs are not feasible due to costs and infectious complications.MethodsThis was a prospective single-centre study of 77 KPD transplantations (25 two-way, 7 three-way and 1 six-way exchange) from 1 January 2015 to 1 January 2016 of 158 registered donor recipient pairs. During this period, a total of 380 kidney transplantations [71 deceased donor kidney transplantations (DDKTs), 309 LDKTs] were performed. The reasons for opting for KPD were ABO incompatibility (n = 45), sensitization (n = 26) and better matching (n = 6).ResultsKPD matching was facilitated in 62% (n = 98) of transplants. In all, 48.7% (n = 77) of the transplants were completed in 2015, whereas 13.3% (n = 21) of the matched patients were to undergo transplant surgery in early 2016 after getting legal permission. The waiting time for KPD was shorter compared with DDKT. The death-censored graft survival and patient survival were 98.7% (n = 76) and 93.5% (n = 72), respectively. In all, 14.2% (n = 11) of patients had acute rejection. Match rates among sensitized (n = 60) and O group patients (n = 62) were 58.3% (n = 35) and 41.9% (n = 26), respectively. Of these, 43.3% (n = 26) and 29% (n = 18) of transplants were completed and 15% (n = 9) and 12.9% (n = 8), respectively, are waiting for legal permission.ConclusionsLDKT increased by 25% in 1 year in our single-centre KPD programme. Our key to success was the formation of a KPD registry, awareness and active counselling programs and developing a dedicated team.

Paired Donation Improves Kidney Transplantation Rate- A Single Centre One Year Experience of 56 Kidney Paired Donations.

Background:Because access to transplantation with HLA-desensitization protocols and ABO incompatible transplantation is very limited due to high costs and increased risk of infections from more intense immunosuppression, kidney paired donation (KPD)promises hope to a growing number of end stage renal disease (ESRD) patients. KPD is feasible for any center performing living donor renal transplantation (LDRT). Materials and methods: We present a government and Institutional Ethical Review Board approved study of 56 end stage renal disease (ESRD) patients [25 two-way and 2 three-way pairs] who consented to participate in KPD transplantation at our center in 2013. They were performed to avoid blood group incompatibility (n=52) or positive cross-match (n=4). All patients had anatomic, functional and immunologically comparable donors. Patient ABO type was A (n=24), B (n=22), AB (n=2) and O (n=8). Donor ABO blood group type was A (n=23), B (n=20), AB (n=2) and O (n=11). Results: Commonest original disease leading to ESRD was hypertension (n=23), chronic glomerulonephritis (n=12) and diabetic nephropathy (n=4). Laparoscopic donor nephrectomy was performed in 54 donors. The waiting time in KPD is short(less than 3 months) as compared to deceased donor transplantation (30 months). Median warm ischemia time, cold ischemia time and anastomosis time were 165 seconds, 66 minutes and 33 minutes respectively. Donor relationships were spousal (n= 40), parental (n=13) or others (n=3), with median HLA match of 1. Graft survival was 100 %. Three patients died with functioning graft due to sepsis and cardiac disease, and 16% had biopsy proven acute rejection. Mean serum creatinine at last follow-up was 1.2 mg/dl. Conclusion KPD is viable, legal and rapidly growing modality for facilitating LDRT for patients who are incompatible with their healthy, willing living donor. To our knowledge, it is largest single-center report from developing country.

The OPTN Kidney Paired Donation Pilot Program (KPDPP): Reaching the Tipping Point in 2013.

Background: U.S. living donor transplants (txs) reported as paired donations increased from 34 in 2004 to 527 in 2012. The OPTN KPDPP was launched in 2010 after KPD was determined not to violate the “valuable consideration” clause in NOTA. The program continues to make important policy and online system enhancements to increase transplant opportunities for patients with willing but incompatible living donors. This report highlights progress made by the OPTN KPDPP in participation, match offers, and txs. Methods: We analyzed tx candidate (TC) and living donor (LD) data submitted from Oct 2010 - Nov 2013 by tx centers participating in the OPTN KPDPP. 2-way, 3-way and chain exchanges were found using algorithms developed by Carnegie Mellon and Johns Hopkins Universities. Match success rates were defined as the percentage of matches (one TC and his matched donor) that were accepted and led to a transplant. Results: Through Nov 2013, 133 (58%) of 231 LD tx programs have agreed to participate with 92 (40%) having entered at least 1 pair. Over 900 TCs and LDs have been entered, with over 220 eligible pairs consistently participating in each weekly match run. In 2013, on average 82 matches were found each quarter with 5% of TCs finding a match in each run. Txs increased by 420% from 10 in 2012 to 52 in 2013, even as 64% of TCs entered were highly sensitized (HS), with CPRA≥80%. Txs included 23 HS TCs. Ethnic minorities comprised 34% of txs.Figure: No Caption available.The dramatic rise in transplants can be attributed to an increased number of matches being found coupled with a rise in the match success rate from 3% in 2012 to 10% in 2013. Conclusion: With the majority of the U.S. LD tx programs now participating, the OPTN KPDPP appears to have reached a tipping point in 2013, producing increasingly more txs, including for difficult-to-match and minority TCs. Though the match success rate has risen, the OPTN KPD Work Group continues to work on ways to increase the rate beyond the current 10%. The OPTN KPDPP is a robust, increasingly successful KPD program available to all LKD programs.

2133 ANALYSIS OF FAILURE TO CONVERT COMPUTER-IDENTIFIED MATCHES INTO TRANSPLANTS IN A MULTIREGIONAL KIDNEY PAIRED DONATION REGISTRY

You have accessJournal of UrologyTransplantation & Vascular Surgery: Renal Transplantation, Vascular Surgery I1 Apr 20122133 ANALYSIS OF FAILURE TO CONVERT COMPUTER-IDENTIFIED MATCHES INTO TRANSPLANTS IN A MULTIREGIONAL KIDNEY PAIRED DONATION REGISTRY Victor Kapoor, David Fumo, Laurie Reece, Susan Rees, and Michael Rees Victor KapoorVictor Kapoor Toledo, OH More articles by this author , David FumoDavid Fumo Toledo, OH More articles by this author , Laurie ReeceLaurie Reece Maumee, OH More articles by this author , Susan ReesSusan Rees Maumee, OH More articles by this author , and Michael ReesMichael Rees Toledo, OH More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.2303AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Many potential computer-identified kidney paired donation (KPD) exchanges fail to culminate in actual transplantations. Here we explored reasons for failure, as well as the success rates of exchanges and Non-simultaneous Extended Altruistic Donor (NEAD) chains. The overall success rate of one-way exchanges comprising these solutions was also found. METHODS Kidney transplant candidates and incompatible donor characteristics were entered into a web-based matching program. Since February 2008, computer match runs have been performed every 4-6 weeks generating a solution that optimizes for quality and quantity of transplants in 2-, 3- and 4-way exchanges as well as NEAD chains. These computer-identified offers were analyzed for reasons for failure, and the offers, as well as the one-way exchanges that comprised these offers, were followed to failure or transplant. RESULTS From February 2008 to June 2011, 40 match runs resulted in 59 transplants. Of the 59 transplants performed, 16 resulted from 2-way paired donations, 6 transplants resulted from two 3-way exchanges, and the remaining 37 transplants were performed through NEAD chains. The overall success rate of offers between January 2008 and June 2011 was 22% (31/141), whereas the one-way exchange success rate was 14% (59/417). 58% (207/358) of 1-way exchanges failed due to dependency on other one-way exchanges within an offer. 42% (151/358) of 1-way exchanges failed due to an identifiable reason for failure. These identifiable reasons for failure included: transplant center withdrawal (30%), recipient withdrawal (23%), positive crossmatch (21%), donor withdrawal (13%), and other (13%). These identifiable reasons of failure were subcategorized to understand why offers are not resulting in a higher number of transplants. CONCLUSIONS We have observed an unexpectedly high failure rate to convert computer-identified KPD matches into transplants due to a variety of reasons. Understanding these reasons has allowed us to modify our software to incorporate a centralized tissue typing laboratory and develop a process of offering preliminary combinations for transplant center evaluation prior to optimizing a final solution. Thus, only acceptable and crossmatch negative one-way combinations are used to construct more robust final offers. As a result, we have substantially improved our conversion rate and the number of transplants so that as of November 2011 we have performed a total of 110 transplants. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e861-e862 Peer Review Report Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Victor Kapoor Toledo, OH More articles by this author David Fumo Toledo, OH More articles by this author Laurie Reece Maumee, OH More articles by this author Susan Rees Maumee, OH More articles by this author Michael Rees Toledo, OH More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Hidden Selection Bias Deriving From Donor Organ Characteristics Does Not Affect Performance Evaluations of Kidney Transplant Centers

Transplant center performance evaluations have garnered substantial attention in recent years. Among sources of bias that may affect measured performance are underlying characteristics of donor organs. An unresolved question is whether centers accepting higher-risk donations are placed in jeopardy for lower evaluations independent of actual quality of care. The primary aim was to assess whether unmeasured characteristics of donor organs impact risk-adjusted outcomes used for center performance evaluations. The study included adult kidney transplant recipients (n = 53,791) from 1994 to 2008 from a national registry. We compared adjusted graft survival with use of paired-donor kidneys (allocated to high- and low-performing centers) and unpaired donor kidneys to investigate whether measured center performance was consistent with organs derived from the same donor (minimizing the influence of noncodified risk factors). The primary finding was that differences between centers were unaffected by use of paired or unpaired donations (hazard ratio for patients transplanted at high performing centers with paired kidneys = 0.63 [95% CI, 0.53-0.74] and with unpaired kidneys = 0.66 [95% CI, 0.62-0.70], P value for interaction = 0.52). This finding was consistent over 5 consecutive cohorts, based on either concurrent or prospective outcomes and by altering the threshold criteria for identification of performance outliers. Results indicate that underlying selection bias from donor characteristics does not impact transplant center evaluations. This is important evidence that donor selection is not a primary driver for evaluated quality of care among transplant centers and acceptance of higher-risk kidneys should not be perceived as a primary threat to measured performance.

A Nonsimultaneous, Extended, Altruistic-Donor Chain

We report a chain of 10 kidney transplantations, initiated in July 2007 by a single altruistic donor (i.e., a donor without a designated recipient) and coordinated over a period of 8 months by two large paired-donation registries. These transplantations involved six transplantation centers in five states. In the case of five of the transplantations, the donors and their coregistered recipients underwent surgery simultaneously. In the other five cases, "bridge donors" continued the chain as many as 5 months after the coregistered recipients in their own pairs had received transplants. This report of a chain of paired kidney donations, in which the transplantations were not necessarily performed simultaneously, illustrates the potential of this strategy.

Characterization of blood components prepared from whole‐blood donations after a 24‐hour hold with the platelet‐rich plasma method

The preparation of platelet (PLT) concentrates (PCs) from PLT-rich plasma (PRP) requires that whole blood (WB) be processed within 8 hours of collection. Increasing WB storage time to 24 hours would be logistically attractive. This study compares the in vitro quality of blood components prepared from WB stored for 8 and 24 hours at room temperature before processing with the PRP method. WB units were collected from ABO-matched blood donors. To reduce individual variations, paired donations were drawn in parallel, pooled, and split back in the collection bag. One unit was held for 6 to 8 hours and the other for 22 to 24 hours at 20 to 24 degrees C. Prestorage leukoreduced components were prepared with the PRP as intermediate product and analyzed during storage. RBC units prepared after an 8- or 24-hour hold were comparable in terms of hemolysis, sodium, pH, and ATP levels. RBC 2,3- diphosphoglycerate (2,3-DPG) was significantly lower in RBCs prepared from 24-hour hold donations immediately after processing but not after 20 days of storage. Residual white blood cells were approximately fivefold higher (p < 0.05) in 24-hour RBC units. For PCs, measurements for glucose, ATP, lactate, pH, extent of shape change, hypotonic shock response, and CD62p activation were similar. No differences were observed in the von Willebrand factor, factor (F)V, FVIII, and fibrinogen content of fresh-frozen plasma. The decrease in FVIII and RBC 2,3-DPG can be acceptable as a compromise to improve blood component logistics, but leukoreduction efficiency must be improved before considering the adoption of an overnight storage of WB before PRP processing.

Clinical Results From Transplanting Incompatible Live Kidney Donor/Recipient Pairs Using Kidney Paired Donation

First proposed 2 decades ago, live kidney paired donation (KPD) was considered a promising new approach to addressing the shortage of organs for transplantation. Ethical, administrative, and logistical barriers initially proved formidable and prevented the implementation of KPD programs in the United States. To determine the feasibility and effectiveness of KPD for the management of patients with incompatible donors. Prospective series of paired donations matched and transplanted from a pool of blood type or crossmatch incompatible donors and recipients with end-stage renal disease (6 conventional and 4 unconventional KPD transplants) at a US tertiary referral center (between June 2001 and November 2004) with expertise in performing transplants in patients with high immunologic risk. Kidney paired donation and live donor renal transplantation. Patient survival, graft survival, serum creatinine levels, rejection episodes. A total of 22 patients received transplants through 10 paired donations including 2 triple exchanges at Johns Hopkins Hospital. At a median follow-up of 13 months (range, 1-42 months), the patient survival rate was 100% and the graft survival rate was 95.5%. Twenty-one of the 22 patients have functioning grafts with a median 6-month serum creatinine level of 1.2 mg/dL (range, 0.8-1.8 mg/dL) (106.1 micromol/L [range, 70.7-159.1 micromol/L]). There were no instances of antibody-mediated rejection despite the inclusion of 5 patients who were highly sensitized to HLA antigens due to previous exposure to foreign tissue. Four patients developed acute cellular rejection (18%). This series of patients who received transplants from a single-center KPD pool provides evidence that recipients with incompatible live donors, even those with rare blood type combinations or high degrees of HLA antigen sensitization, can receive transplants through KPD with graft survival rates that appear to be equivalent to directed, compatible live donor transplants. If these results can be generalized, broader availability of KPD to the estimated 6000 patients with incompatible donors could result in a large expansion of the donor pool.

Plateletpheresis efficiency: a comparison of the Spectra LRS and AMICUS separators

Optimizing the yields of plateletpheresis by increasing collection efficiencies may provide several benefits: to patients, by increasing the dose in single-donor platelet (SDP) units; to the collection center, by increasing the percentage of components that may be split into double units; and/or to the donor, by reducing the duration of donation. A prospective, randomized study was undertaken to compare the efficiency of platelet collection in paired donations by 21 donors on two cell separators (Spectra LRS, version [v] 5.1; and AMICUS, v2.37). The order of donation was randomly assigned; donations were performed at least 2 weeks apart. A fixed blood volume (4000 mL) was processed by utilizing standard protocols. Findings were confirmed in a retrospective, matched study that compared the two separators by using fixed collection times (90 min). The AMICUS and Spectra LRS separators consistently produced white cell-reduced (<1 x 10(6) white cells) components. The AMICUS harvested 32 percent more platelets on average (median, 4.9 x 10(11); range, 1.5-8.7 x 10(11)) than the Spectra LRS (median, 3.7 x 10(11); range, 2.1-7.7 x 10(11)) (p = 0.03), with mean times of 71.5 and 66.0 minutes (p = 0.03), respectively, to process 4000 mL. Mild donor reactions tended to be more common on the AMICUS separator, which used significantly more ACD (median 482 mL vs. 389 mL; p<0.0001) than on the Spectra LRS. The AMICUS separator harvested more platelets per unit of blood volume processed than the Spectra LRS. Possible benefits include increased dose in each single-donor unit, increased double-unit harvests, and/or shorter donation time.

Plateletpheresis with the COBE spectra single needle access option

A group of modifications, including a reservoir bag in the return circuit, has been devised to allow single needle plateletpheresis with the COBE Spectra. We compared the number and quality of platelets collected from 10 subjects in paired donations with single and dual needle protocols. There was no evidence of hemolysis with either protocol. Mean (+/- SD) platelet yields were 3.61 +/- 1.47 x 10(11) with two needles and 3.31 +/- 1.31 x 10(11) with the single needle procedure (P = .13). Mean leukocyte levels (standard manual counting chamber) were 1.0 +/- 1.7 x 10(7) and 1.2 +/- 1.0 x 10(7), respectively (p = .78). pH values during storage were acceptable in both groups of concentrates, and there were no significant differences between the single needle and dual needle concentrates in morphology scores or beta-thromboglobulin levels at 0, 1, 3, or 5 days of storage. Thus the single needle modification produced platelets that were comparable in quantity and quality to those from the standard dual needle plateletpheresis protocol.