ALBERT

Description: Abstract 1511 Poster Board I-534 Background What determines the degree of hemolysis and of anemia in patients with hemoglobin SS is not fully known. The rate of hemolysis and severity of anemia are ameliorated by the presence of alpha thalassemia and by higher hemoglobin F percentage. Mild G6PD deficiency in the form of G6PD-202/-376 may be associated with episodic hemolysis in individuals of African descent, but past studies indicated little influence of G6PD-202/-376 on the degree of hemolysis and anemia in sickle cell disease patients (1,2). In this study we examined the roles of single and double α-globin deletions and G6PD-202/-376 on the degree of hemolysis and the hemoglobin concentration in hemoglobin SS patients. Methods Two hundred sixty two children and adolescents with hemoglobin SS were recruited at three tertiary medical centers and studied at steady state. Principal component analysis was used to develop a hemolytic component from concentrations of lactate dehydrogenase, aspartate aminotransferase and bilirubin. PCR was used to determine the presence of α-thalassemia and G6PD-202/-376. Multivariate models were employed to determine the independent effects of these genotypes on hemoglobin concentration and degree of hemolysis. Results Single a-globin deletion was associated with an estimated 0.4 g/dL increase in steady-state hemoglobin concentration and double α-globin gene deletion with a 0.8 g/dL increase (P = 0.005 for trend) due to, progressively lower degrees of hemolysis (P = 0.004). G6PD-202/-376 was associated with an estimated 0.7 g/dL decrease in the hemoglobin concentration (P = 0.003) (Figure 1a), but this observation could not be explained by increased hemolysis. Rather, the reticulocyte count was an estimated 22% lower with G6PD-202/-376 (P = 0.032) (Figure 1b). Discussion G6PD -202/-376 may be associated with lower hemoglobin concentration in sickle cell anemia and the mechanism is probably impaired erythropoiesis rather than hemolysis. A recent study (3) indicates that G6PD is needed for definitive erythropoiesis as well as for normal survival of red blood cells in the periphery. Our present findings raise the possibility that, in the setting of the markedly increased erythropoiesis of sickle cell anemia, G6PD-202/-376 may result in impairment in erythropoiesis that is discernible in the peripheral blood hemoglobin concentration. Disclosures No relevant conflicts of interest to declare.

Description: Transcranial Doppler (TCD) screening in children with sickle cell anemia (SCA) identifies abnormally elevated cerebral artery flow velocities that confer an elevated risk for primary stroke. Chronic transfusions offer effective stroke prophylaxis in this setting, but must be continued indefinitely and lead to transfusional iron overload. An alternative treatment strategy that offers similar effective protection against primary stroke, and provides control of iron overload, is needed. TCD With Transfusions Changing to Hydroxyurea (TWiTCH, NCT01425307) was an NHLBI-funded Phase III multicenter randomized clinical trial comparing 24-months of standard treatment (transfusions) to alternative treatment (hydroxyurea) in children with SCA and abnormal TCD velocities. All eligible children had received at least 12 months of transfusions. TWiTCH had a non-inferiority trial design; the primary study endpoint was the 24-month TCD velocity obtained from a linear mixed model, controlling for baseline (enrollment) values, with a non-inferiority margin of 15 cm/sec. The transfusion arm maintained children at HbS

Description: Background: Clofarabine, a next generation nucleoside analogue, was well tolerated and demonstrated activity in adult and pediatric Phase I trials conducted in heavily pretreated leukemia patients. Multicenter Phase II studies in pediatric leukemia have completed accrual in the US and are reported here. Methods: Two Phase 2, multicenter, open-label studies were conducted with clofarabine in children with refractory or relapsed ALL or AML. Clofarabine was administered intravenously over 2 hours at 52 mg/m2/day for 5 consecutive days. Cycles were repeated every 2 to 6 weeks based on response and toxicity. Results: The studies enrolled 100 patients (60 ALL and 40 AML). Currently, data are available for 84 patients (49 ALL, 35 AML). Median age is 12 years (range 1 to 22 years) and median number of prior regimens is 3 (range 1 to 6). Thirty-nine percent had received prior bone marrow transplant (BMT). As determined by independent review, preliminary data indicate overall response rates of 31% in ALL (6 CR, 4 CRp, and 5 PR) and 26% in AML (1 CRp and 8 PR). Median duration of remission for ALL is 9.7 weeks (range 1.0 to 28.6) and for AML is 16.2 weeks (range 1.7 to 56.6+). Thirteen of 24 responding patients (54%) proceeded to BMT. Median survival was 42 weeks (range 7.0 to 63.1+) for responding ALL patients (CR+CRp+PR) and 39 weeks (range 7.7 to 93.6+) for responding AML patients (CRp+PR). Patients who failed treatment or were non-evaluable had shorter median survival; 7.4 weeks (range 0.9 to 40.1+) and 12.4 weeks (range 1.6 to 84.9+) for ALL and AML, respectively. Among the patients who were refractory to the last prior chemotherapy, 7/30 (23%) with ALL and 4/22 (18%) with AML achieved a response with clofarabine. Median duration of remission in these patients is 4.6 weeks (range 2.3 to 24.4+) for ALL and 20 weeks (range 1.7 to 56.6+) for AML. Most drug-related adverse events were transient including febrile neutropenia, diarrhea, nausea/vomiting, fever, skin rash, headache, elevation in liver enzymes and bilirubin, and infusion-related flushing and anxiety. Conclusions: Clofarabine is active as a single agent in pediatric ALL and AML that are refractory to intensive salvage regimens. The overall safety profile is similar to that reported in other pediatric salvage studies. Clofarabine in combination with standard chemotherapy is currently under investigation in children.

Description: Introduction: The multicenter phase 3 randomized clinical trial TCD With Transfusions Changing to Hydroxyurea (TWiTCH, NCT01425307) investigated whether hydroxyurea could maintain TCD velocities and prevent stroke in children with sickle cell anemia and abnormal TCD velocities. The trial was stopped early after reaching the primary endpoint, when the average TCD velocity in the alternative (hydroxyurea) arm was found to be non-inferior and even slightly better (138 versus 143 cm/sec) than the standard (transfusion) arm. A planned secondary analysis was to determine the variation in serial TCD velocity measurements for individual study participants, to document the normal TCD velocity fluctuations that occur and to inform the need for frequent TCD evaluations in this clinical setting. Methods: All TCD examinations collected in TWiTCH were analyzed for the maximum time-averaged mean velocity (TAMV) measured in the main intracranial arteries. TCD studies were performed by certified examiners using identical non-imaging instruments, no more than one week before a scheduled transfusion or phlebotomy procedure. Measurements on the index side, defined as the cerebral hemisphere with the higher mean arterial velocity at baseline assessment, were used for these statistical analyses. TCD values were analyzed according to four phases of the trial: (1) screening with three monthly TCD examinations performed at Weeks -8, -4, and 0 before randomization; (2) initial treatment period (hydroxyurea dose escalation with overlap transfusions or transfusions only) with three quarterly TCD measurements at Weeks 12, 24, and 36; (3) steady-state treatment period (hydroxyurea only or transfusions only) with four quarterly TCD measurements at Weeks 48, 60, 72, and 84; and (4) study exit with three monthly TCD examinations performed at Weeks 96, 100, and 104 or during the accelerated close-out period. The within-patient variance and standard deviation of the TAMV values were found using a linear mixed model, which was calculated using SAS Version 9.3. Results: TAMV measurements on the index side from 1458 TCD examinations on 121 randomized patients formed the overall dataset. TAMV values ≥170 cm/sec were identified in 140 measurements on 40 children (9.6% of TCD values) and exceeded 200 cm/sec in 1.8% of examinations (26 values, 8 children) during the study treatment phase. The within-patient TCD variation, representing fluctuation of repeated TCD measurements in the same study participant, was 12.0 cm/sec for the entire cohort during the initial screening phase (363 TCD measurements). In the initial treatment phase, TCD variation in the hydroxyurea arm (180 values, 60 children) was 10.5 cm/sec, similar to 10.2 cm/sec on the transfusion arm (183 values, 61 children). In the steady-state treatment phase, the TCD variation in the hydroxyurea arm was 10.2 cm/sec (207 values, 57 children), compared to 12.3 cm/sec on the transfusion arm (212 values, 58 children). In the final exit phase, TCD variation in the hydroxyurea arm was 9.8 cm/sec (155 values, 58 children), similar to 10.2 cm/sec on the standard arm (155 values, 57 children). TCD variation was greater with higher baseline TCD velocity and shorter transfusion duration, but was not affected by age or gender. For example, participants with baseline TCD velocity of

Description: Background Total pancreatectomy with islet autotransplantation (TPIAT) is a surgical treatment for chronic recurrent pancreatitis that involves splenectomy, pancreatectomy and creation of a Roux-en-Y, followed by re-injection of the pancreatic islets into the portal vein. Postoperatively, patients develop a sustained and extreme thrombocytosis (ExT) with platelets ≥1000 K/μL, a response more exaggerated than the typical post-splenectomy course (Gurria JP et al, Pancreas 2019). Empiric aspirin (antiplatelet effect) and hydroxyurea (cytoreduction) are initiated postoperatively per a standard protocol. The pharmacokinetic (PK) and pharmacodynamic (PD) profiles of hydroxyurea have not been studied in children other than young children with sickle cell disease; neither dose nor dose interval have been evaluated in TPIAT patients. Recently a population PK model was developed to support individualized hydroxyurea dosing in patients with sickle cell anemia (SCA; Dong M et al, Br J Clin Pharmacol 2016). In a prospective evaluation as part of the Therapeutic Response Evaluation and Adherence Trial (TREAT, McGann PT et al, Am J Hematol 2019), PK-guided individualized dosing resulted in better clinical and laboratory benefits than with conventional weight-based dosing. This study aimed to determine if a hydroxyurea PK model could be developed for non-SCA children dosed postoperatively for control of TPIAT-associated ExT, and if so, to compare it to previously published models for SCA. Methods A prospective single-site pilot study was performed in patients ages 0-21 years who underwent TPIAT between April 2018 and June 2019. Whole blood was collected via finger stick or venipuncture at 3 time points (20 minutes, 1 hour, 4 hours) after the initial hydroxyurea dose (15-20 mg/kg), given between postoperative day 5-7 (PK1). Plasma hydroxyurea was quantified by high performance liquid chromatography on 150-200 μL plasma. Testing was repeated once 2-6 months postoperatively (PK2) to determine whether PK profiles changed over time in relation to surgery. PK analyses and estimation of the area under the concentration-time curve (AUC) as a measure of exposure were performed using MW/Pharm (Mediware, Prague, Czech Republic). PK data from HUSTLE (NCT00305175) were used for comparison to SCA patients. Results Of 19 enrolled subjects, 15 had evaluable results: 7 had both PK collections while 8 had a single collection (5 only had PK1, 3 only had PK2). All 5 patients with only PK1 measurements had discontinued hydroxyurea by the time PK2 samples would have been collected, whereas those with only PK2 all had unsuccessful PK1 collection attempts. Mean age was 13.5 years [standard deviation (SD) 5] with mean weight-based dose 14 mg/kg (SD 3.4). Serum creatinine was normal for age in all patients. Hydroxyurea suspension was delivered via jejunal tube at PK1 while oral tablets were used at PK2 per surgical protocol. The AUC was 60.1 h*μg/ml at PK1 and 68.6 h*μg/ml at PK2. When compared to HUSTLE cohort (Figure 1), TPIAT subjects overall had lower drug exposure (AUC), worse for PK1 than PK2, especially when hydroxyurea concentration was normalized to dose. TPIAT patients also appear to have had slower absorption, evidenced by still-rising hydroxyurea concentrations after 1 hour, compared to 20-30 minute peak concentrations in HUSTLE. Conclusions TPIAT subjects treated empirically with hydroxyurea to modulate ExT have decreased absorption and overall lower concentrations and drug exposure relative to our SCA population. Lower bioavailability and/or altered absorption may in part be caused by differences in formulation (suspension versus tablet) and route of administration (oral versus jejunal) along with postoperative anatomic changes not present in the SCA cohort, since Roux-en-Y may alter drug absorption and metabolism (Rogers CC et al, Clin Transpl2008). It is unknown whether higher enteral hydroxyurea doses would increase exposure and effect. Additional evaluation of the absorption characteristics and PK/PD of hydroxyurea in TPIAT patients, as well as efficacy, are urgently needed. Figure 1 Disclosures Ware: Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Nova Laboratories: Membership on an entity's Board of Directors or advisory committees; CSL Behring: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: DSMB; Bristol Myers Squibb: Other: Research Drug Donation; Addmedica: Other: Research Drug Donation. OffLabel Disclosure: Hydroxyurea to reduce extreme thrombocytosis after splenectomy/pancreatic islet cell transplant in children

Description: Abstract 243 Susceptibility to encapsulated bacteria, particularly Streptococcus pneumonia, is well known in sickle cell disease (SCD). Hydroxyurea (HU) is commonly used in adults and children with SCD, but, little is known about the effects of HU on immune function in SCD and recommendations for immunization are lacking. As HU reversibly inhibits ribonucleotide reductase, causing cell cycle arrest at the G1-S interface, we postulated that HU might delay the transition from naïve to memory T cells, resulting in a delay in immunologic maturation, with deleterious effects on vaccine responses; therefore, T cell subsets, including conversion of naïve to memory T cells and antibody (Ab) responses to pneumococcal (Pnu), measles, mumps and rubella (MMR) vaccinations were studied during the BABY HUG Trial of HU for infants and toddlers with SCD. Methods: Blood was collected for measurement of: T cell subsets at entry (9–18 mos of age), age 24 mo and exit after 2 yrs of treatment; Pnu Ab levels were measured (by EIA after preabsorption with C-polysaccharide) at entry, before and 2–8 wks after 23-valent polysaccharide (PS) PCV23 vaccine at age 24 mo, and exit; and MMR antibodies at entry, 1–10 weeks after MMR at age 12 mo, age 24 mo and exit. Results: Of the 193 subjects in BABY HUG, T cell subsets were available for 91 HU and 88 placebo (PL) subjects. At entry, there were no significant differences in absolute lymphocyte count (ALC), or % or absolute T cell subsets between the HU and PL groups. At age 24 mo, both groups had an age-related decline in ALC, with significant differences between the HU and PL groups in ALC (5740 vs. 7323/mm3; p=0.003), absolute CD4 cells (1912 vs. 2247/mm3; p=0.022) and memory CD4 cells (392 vs. 487/mm3; p=0.003). The same pattern was seen at exit for ALC (4836 vs. 5764/mm3; p=0.015), absolute CD4 cells (1510 vs. 1747/mm3; p=0.043) and memory CD4 cells (360 vs. 444/mm3; p=0.003). IgG Ab levels to Pnu antigens were measured at entry [after 3 doses of PS/protein conjugate (PC) PCV7 containing Pnu PS type 26 (6B), but not 51 (7F)], before and after immunization with PS PCV23 vaccine at 24 mo, and at exit, with no significant differences between the HU and PL groups in mean Ab levels at any time point for either serotype (Fig 1&2). For those immunized with MMR prior to study treatment, there were no differences in % immune for measles, mumps, or rubella between the HU and PL groups at any time point. For 40 HU and 38 PL subjects immunized after starting study treatment, there was a smaller % of HU-treated children with protective response to measles vaccine 1 – 10 wks after immunization [HU 71.4% (10/14) vs. PL 100% (24/24); p=0.014]. Response to mumps [HU 78.6% (11/14) vs. PL 91.7% (22/24)] and rubella [HU 66.7% (10/15) vs. PL 92% (23/25)] vaccines showed similar trends, but no statistical significance. The HU vs. PL difference in failure of response to at least one vaccine virus was of similar significance (p = 0.021) to that of measles alone. By age 24 mo, there were no significant differences in response to MMR (89.7 to 100%). Mean Ab levels to measles and rubella were also significantly lower in the HU group 1–10 wks after immunization (p=0.005 and p=0.011, respectively). Conclusions: HU given to infants and young children with SCD causes a reduction in ALC, CD4 T cell and memory T cell counts. Additional monitoring of HU-treated children with SCD for these and related T cell parameters is warranted until the biological effects on immunity are known with certainty. Response to Pnu vaccine was not affected by HU therapy, suggesting that there is no increased risk for Pnu sepsis in infants and children with SCD treated with HU, consistent with the clinical results in the BABY HUG trial. Although the sample was small, a delay in achieving protective measles Ab levels was seen in the HU group, and possibly for mumps and rubella. This delay cannot be estimated precisely, due to study design, but Ab levels to all 3 viruses were similar at exit, indicating that effective immunization can be achieved despite HU use. For endemic or local epidemics of measles, mumps, rubella or other pathogens requiring immunization, adherence to recommended accelerated immunization schedules will be especially important for children with SCD treated with HU. Disclosures: Off Label Use: Off-label use of hydroxyurea in infants and children. Casella:Adventrx: Consultancy, Research Funding.

Description: Total pancreatectomy with islet autotransplantation (TPIAT) is a therapeutic option for debilitating acute recurrent or chronic pancreatitis. While postoperative diabetes and pain outcomes are well-described in these patients, the hematologic outcomes have not been thoroughly examined. Specifically, the natural history and optimal management of the nearly universal post-IAT extreme thrombocytosis (platelets 〉1000 K/μL) beginning within days of surgery and often lasting for months remains enigmatic. Concern for thrombosis risk from the extreme thrombocytosis has prompted empiric, widely-employed pharmacologic alteration of platelet count (hydroxyurea) and function (aspirin, ASA); however, the optimal dosing strategy and efficacy of these therapies after IAT are poorly characterized. Patients who underwent TPIAT (n=28) or subtotal pancreatectomy with islet autotransplantation (n=2), all with splenectomy, at Cincinnati Children's Hospital Medical Center between January 1, 2015 and April 30, 2018 were retrospectively reviewed. Hydroxyurea management strategies, hematologic trends, and hydroxyurea side effects were evaluated. The mean age of the patients was 12.3 years (range 3-19 years). All started ASA on post-operative day (POD) 2-3 at a median daily dose of 2 mg/kg [Interquartile Range (IQR) 1.7-2.13). This was continued until hydroxyurea was discontinued and platelet count remained normal for 4 weeks. All received prophylactic heparin and later enoxaparin post-operatively per protocol until discharge. VerifyNow® ASA testing was performed after aspirin initiation, with dose increases as necessary to reach therapeutic result. Among the 30 patients evaluated, 26 developed extreme thrombocytosis (median maximum platelet count 1298 K/μL, IQR 1046-1563), peaking at a median of 16 days (IQR 14-20). Two patients developed portal vein thromboses (POD 4 in a 13 year old with platelets 321 K/μL at diagnosis, and POD 11 in a 15 year old with platelets 1458 K/μL at diagnosis, respectively). Both patients had clot resolution while on therapeutic enoxaparin for 3 months. On July 1, 2016, a more standardized regimen for aspirin and hydroxyurea initiation, dose modification and weaning was implemented. These changes resulted in earlier hydroxyurea initiation [median 7 (IQR 6-8) versus 9 (IQR 8-10) days postoperatively, p=0.03] at lower platelet counts [median 529 (IQR 501-600) versus 938 (IQR 776-1085) K/μL, p1000 K/μL, while all patients before standardization had extreme thrombocytosis. VerifyNow® ASA testing was performed earlier after standardization (POD 6 versus 7, p=0.01) with similar percentages of non-therapeutic ASA measurements in each group (22 versus 19%). The MCV rose a median 13 fL (IQR 8.75-20) while on hydroxyurea. With the current sample size, no statistically significant differences were detected between the two groups for maximum hydroxyurea dose, treatment duration, maximal platelet count, the number of patients with multiple episodes of extreme thrombocytosis, or number of days with extreme thrombocytosis. Of the 25 patients who were fully weaned off hydroxyurea as of July 31, 2018, the therapeutic course was a median 175 days (IQR 90-259). Median absolute neutrophil count (ANC) was 4140 K/μL (IQR 2700-7080). Neutropenia (ANC

Description: Abstract 3216 Fetal hemoglobin (HbF) is the major genetic modifier of clinical course of sickle cell anemia (homozygosity for HBB glu6val). HbF level is also an important predictor of mortality. If it were possible to know at birth the HbF level likely to be present after stabilization of this measurement at about age 5 years, then an improved prognosis might be given and HbF-inducing treatments better informed. Levels of HbF in adults are highly heritable and the production of HbF is genetically regulated by several quantitative trait loci and by genetic elements linked to the HBB gene cluster. One of the most popular approaches to genetic risk prediction uses a summary of the risk alleles in the form of a genetic risk score (GRS) that is used as a covariate of the genetic prediction model. We present the development of a GRS for HbF in 841 patients from the Cooperative Study of Sickle Cell Disease (CSSCD) cohort patients and assessed its ability to predict HbF values in three independent cohorts that included PUSH (N=77), Walk-PHaSST (N=181), and C-Data from the Comprehensive Sickle Cell Centers program (N= 127). We used the results of a genome-wide association study (GWAS) of HbF in sickle cell anemia, in which patients were genotyped using the 610K Illumina array, and association of each of the ∼550K SNPs with HbF was tested using a linear regression model with gender adjusted additive genetic effects. To build the GRS, we sorted SNPs by increasing p-value, starting from the most significant SNP associated with HbF (rs766432, p-value=2.61×10−21), and pruned the list by removing SNPs in high LD (r2 〉 0.8). We then used this list of SNPs to generate a sequence of nested GRS. We started with the GRS that included only the most significant SNP and generated the second GRS by adding the second SNP from the list of SNPs. The third GRS was generated by adding the 3rd SNP from the list of SNPs to the second GRS, and so on. We repeated this analysis including up to 10,000 SNPs (p-value〈 .02185) and hence generated 10,000 GRS, for each of the subjects in the CSSCD. Each of these GRS was included as covariate in a linear regression model and the regression coefficients of the resultant 10,000 linear regression models were estimated using Least Squares methods in the CSSCD data. The predictive value of these GRS models was then evaluated in three independent cohorts. In this evaluation, we computed the 10,000 GRS for each subjects in each data sets, and then used the 10,000 regression models estimated in the CSSCD data set to compute the expected HbF value of patients, given their GRS. We then assessed the predictive accuracy by computing the correlation between the observed and predicted values of HbF. To produce more stable predictions, we also created ensembles of predictive models. An ensemble of the first 14 GRS models including 14 SNPs had the best predictive value in all 3 data sets and explains 23.4% of the variability in HbF; the correlation between the predicted HbF and observed HbF was 0.44, 0.28 and 0.39 in the three different cohorts. Of these 14 SNPs, 6 were located in BCL11A; other SNPs were located in the olfactory receptor region and the in chromosome 11p15 and the site of the HBB gene cluster and were found previously to be associated with HbF. We next compared these results to predictive models in which we included gender, coincident alpha thalassemia, and HBB haplotypes for prediction. The model including gender and alpha thalassemia explained only 2.6% of the variability of HbF in the discovery cohort and the model including HBB haplotypes explained 2.35% of the variability of HbF in the discovery cohort and neither model showed a significant correlation between the predicted and observed HbF in the three other cohorts. In addition, combining the non-genetic information with the GRS did not help to explain more of the variability in HbF. With as few as 14 SNPs we can explain more of the variability in HbF and do a better job of prediction in comparison to using other non-genetic risk factors or genome-wide significant SNPs; however, we still cannot explain all of the variability in HbF that is due to heritability. These results suggest that knowing the genotype of a few SNPs can help to predict HbF that after they have stabilized. Prediction of HbF at an early age has the potential to help foretell some features of the severity of the clinical course of the disease and aid to optimize the clinical management of patients. Disclosures: No relevant conflicts of interest to declare.

Description: Introduction: Enoxaparin (low molecular weight heparin, LMWH) is the most commonly prescribed anticoagulant for pediatric patients with venous thromboembolism (VTE) (Goldenberg et al. 2015). The gold-standard LMWH activity (anti-Xa activity) assays differ in whether they add exogenous antithrombin (AT) or dextran sulfate (Ignjatovic et al. 2007). Adding AT would "standardize" results in patients with low antithrombin, such as infants and asparaginase-treated patients (Mitchell et al 2010); however, questions remain about which assay best reflects the patient's anticoagulation effect and the degree of discrepancy between assays. We assessed LMWH activity in residual plasma samples from a cohort of anticoagulated pediatric acute lymphoblastic leukemia and lymphoma (ALL) patients, with history of VTE and variable AT levels, on four platforms (two instruments and their kits +/- exogenous AT). Methods: We analyzed 60 de-identified residual plasma samples from 12 anticoagulated ALL patients (2-19 years. Mean 13.75 yr) who had AT levels obtained for clinical care. All consented to the IRB-approved Oncology Tissue Repository. LMWH activity was assessed on Siemens and Stago instruments using their recommended kits that did or did not contain exogenous AT (Table 1), according to manufacturer recommendations, by experienced laboratorians. Results: Results were interpretable on 236/240 with 4 rejected for lipemia. Mean AT activity was 80 (42-138 ng/ml, lab normal 〉81%). Correlation was acceptable for the published kit ranges of LMWH activity when comparing kits +AT (Berichrom® to Stachrom®, r=0.82, p

Description: Abstract 1647 Clinical B12 (cobalamin) deficiency occurs in sickle cell disease (SCD) but it is uncommon (NEJM 2003;348:2204). Several publications report lower serum B12 concentrations in SCD subjects than in controls (Acta Haematol 1984;71:299; J Intern Med 1995;237:551; J Nat Med Assoc 2006;98:352). However, other studies do not show these differences (Am J Hematol 2004;76:114; South Med J 2004;97:149; J Am Coll Nutr 2000;19:608). Serum transcobalamin concentrations are high in SCD (Scand J Haematol 1983;30:135; Acat Haematol 1989;81:117) so that one would expect higher than normal B12 levels in these patients. We measured serum B12 concentrations in 467 children and adolescents with SCD and in 69 control subjects matched for age, sex, and ethnicity. All subjects were enrolled in the PUSH protocol, a multicenter study for determining the prevalence and significance of pulmonary hypertension in children with SCD. The median serum B12 concentration in SCD was lower than in controls (960 vs. 1094 pg/ml, p=0.003). No patient had a serum B12 value lower than 227 pg/ml (3 SD below the mean of control subjects) and sickle genotype did not affect B12 concentration. Univariate analysis in children with the Hb SS genotype (N=343) showed that age, body mass index, serum creatinine (all three p=0.0001), and red cell MCV (p=0.025) were each inversely correlated with B12 levels, and this suggested the possibility that as children grow, their B12 requirements increase. In SS children higher leukocyte counts, serum AST, and serum ALT were all associated with higher B12 levels (p=0.005, p=0.0001, and 0.011, respectively), while blood Hb concentration, a-thalassemia status, Hb F %, platelet count, and hemolytic parameters were unrelated to serum B12. The median B12 level in SS children (941 pg/ml) remained significantly lower than that of controls even after adjustment for age and WBC. Children with Hb SS who were taking hydroxyurea had significantly lower median B12 levels (845 pg/ml, N=141) than SS children not on this drug (992 pg/ml, N=200 p=0.027) (Figure) but after adjustment for age and WBC this difference was no longer significant (p=0.5). These results suggest that (a) children with SCD have lower, though still normal, serum B12 concentrations than healthy subjects, (b) this difference is not explained by SCD leukocytosis so that it could represent increased B12 requirements, and (c) hydroxyurea treatment reduces B12 levels even further probably as a result of its lowering effect on leukocyte count. However, because hydroxyurea was not given in a randomized manner, we cannot exclude the confounding effect of age on B12 level in hydroxurea treated subjects. Since we and others (Acat Haematol 1989;81:117) show that in SCD serum B12 decreases with age, as is the case also in non-SCD individuals (Am J Clin Nutr 1997;66:741), it would seem prudent to monitor cobalamin levels in SCD adults, particularly in older subjects and in those taking hydroxyurea. Disclosures: No relevant conflicts of interest to declare.