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Objective To determine whether long-term transfusion improves growth in children with sickle cell anemia. Study design In the Stroke Prevention Trial for Sickle Cell Anemia Study, patients were randomized to receive long-term transfusion (CTX) or standard care (STC). Transfusions were administered every 3 to 5 weeks, and hemoglobin S levels were maintained at 30% pretransfusion for an average of 2 years. Serial height and weight measurements (obtained every 3 months), body mass index (BMI) values, and growth z-scores were analyzed. Results Children in the CTX (n=53) and STC (n=41) groups were similar at baseline. After 24 months, the z-scores for height, weight, and BMI of those receiving CTX had improved significantly, whereas no changes occurred in the STC group. Patients in the CTX group approached normal height-for-age and weight-for-age z-scores. Patients from a large historical control group had significantly lower weight and height growth velocities than patients in the CTX group. Conclusions Patients in the Stroke Prevention Trial for Sickle Cell Anemia Study who received CTX had improved height and weight and BMI over a 2-year period. Higher hemoglobin levels resulting from transfusion may improve growth by lowering energy expenditure. In addition to the prevention of vasoocclusive events, CTX results in significant improvement in the growth of children with sickle cell disease.

Objective: To test the hypothesis that children with sickle cell disease (SCD) who have an initial stroke temporally unrelated to another medical event are at higher risk for recurrent stroke than are children who had strokes temporally related to medical events. Methods: A retrospective cohort study of children with SCD and stroke who received regularly scheduled blood transfusions for a minimum of 5 years was conducted. Medical records were examined for the documentation of antecedent or concurrent medical events (hypertension, acute chest syndrome, aplastic crisis, fever associated with infection, exchange transfusion) associated with physician contact within 14 days before the initial stroke. Results: A total of 137 pediatric patients from 14 centers were studied. Mean age at first stroke was 6.3 years (1.4 to 14.0 years) with mean follow-up of 10.1 years (5 to 24 years). Thirty-one (22%) patients had a second stroke (2.2 per 100 patient years); 26 patients had an identified medical or concurrent event associated with their initial stroke. None of these patients had recurrent stroke 2 or more years after the initial event. The remaining 111 patients had an ongoing risk of recurrent stroke (1.9 per 100 patient-years) despite long-term transfusions ( P = .038). Conclusions: The absence of an antecedent or concurrent medical event associated with an initial stroke is a major risk factor for subsequent stroke while receiving regular transfusions. (J Pediatr 2002;140:348-54)

Objectives: Although hydroxyurea is effective in treating adults with sickle-cell anemia (SCA), there is concern that it may adversely affect growth in children. We report the growth characteristics of patients in the Phase I-II pediatric hydroxyurea trial (HUG-KIDS) before and during treatment at the maximum tolerated dose for one year. Study design: Children and adolescents with SCA (n = 68), aged 5 to 16 years at baseline, reached the maximum tolerated dose and had serial height, weight, and Tanner stage measurements. Data from the Cooperative Study of Sickle Cell Disease (CSSCD) were used for comparison. Mixed-effects models were used to compare serial measurements as a function of age and group. Results: In girls, there were no significant differences in height or weight among the pretreatment, on-treatment, and CSSCD groups. Compared with the CSSCD group, HUG-KIDS boys were heavier starting at age 9 years, and pretreatment HUG-KIDS boys were taller starting at age 7 years. The Tanner stage transitions took place at appropriate ages. Conclusions: Hydroxyurea treatment had no adverse effect on height or weight gain or pubertal development in school-aged children with SCA. (J Pediatr 2002;140:225-9)

Objective: Hydroxyurea improves hematologic values and decreases vaso-occlusive complications in adults and children with sickle cell anemia (SCA), but has not been tested in infants before the onset of chronic organ dysfunction. We conducted a collaborative pilot trial of hydroxyurea in infants with SCA to assess its (1) feasibility of administration, (2) toxicity, (3) hematologic effects, and (4) effect on spleen function. Study design: Patients with hemoglobin (Hb) SS or Sβ0 thalassemia (n = 28, median age 15 months) received hydroxyurea for 2 years at 20 mg/kg/day. Hydroxyurea was temporarily discontinued for predefined toxicity. Results: Seven patients exited the study early: five for noncompliance or refusal to continue, one for mild stroke, and one for fatal splenic sequestration. The predominant toxicity was transient neutropenia, which was usually associated with a viral-like illness. After 2 years of treatment, mean Hb level = 8.8 g/dL and Hb F = 20.3%, both higher than predicted age-specific levels. Radionuclide splenic uptake was absent in 47% of patients at study completion, compared with predicted functional asplenia in 80% of the patients. Conclusions: Hydroxyurea therapy for infants with SCA is feasible and well tolerated, has hematologic efficacy, and may delay functional asplenia. The potential for hydroxyurea to preserve organ function in SCA should be further evaluated. (J Pediatr 2001;139:790–6)

Objective: To determine whether children with homozygous sickle cell anemia (SCD) who have silent infarcts on magnetic resonance imaging (MRI) of the brain are at increased risk for overt stroke. Methods: We selected patients with homozygous SCD who (1) enrolled in the Cooperative Study of Sickle Cell Disease (CSSCD) before age 6 months, (2) had at least 1 study-mandated brain MRI at age 6 years or older, and (3) had no overt stroke before a first MRI. MRI results and clinical and laboratory parameters were tested as predictors of stroke. Results: Among 248 eligible patients, mean age at first MRI was 8.3 ± 1.9 years, and mean follow-up after baseline MRI was 5.2 ± 2.2 years. Five (8.1%) of 62 patients with silent infarct had strokes compared with 1 (0.5%) of 186 patients without prior silent infarct; incidence per 100 patient-years of follow-up was increased 14-fold (1.45 per 100 patient-years vs 0.11 per 100 patient-years, P = .006). Of several clinical and laboratory parameters examined, silent infarct was the strongest independent predictor of stroke (hazard ratio=7.2, P = .027). Conclusions: Silent infarct identified at age 6 years or older is associated with increased stroke risk. (J Pediatr 2001;139:385-90)

A retrospective cohort study of children with sickle cell anemia (SCA) and strokes was used to test the hypothesis that exchange transfusion at the time of stroke presentation more effectively prevents second strokes than does simple transfusion. Children receiving simple transfusion had a 5-fold greater relative risk (95% confidence interval = 1.3 to 18.6) of second stroke than those receiving exchange transfusion.

OBJECTIVES: (1) To determine serotype-specific IgG antibody responses to reimmunization with pneumococcal polysaccharide vaccine at age 5 years in children with sickle cell anemia and (2) to determine whether continued penicillin prophylaxis had any adverse effects on these responses. STUDY DESIGN: Children with sickle cell anemia, who had been treated with prophylactic penicillin for at least 2 years before their fifth birthday, were randomly selected at age 5 years to continue penicillin prophylaxis or to receive placebotreatment. These children had been immunized once or twice in early childhood with pneumococcal polysaccharide vaccine and were reimmunized at the time of randomization. RESULTS: Serotype-specific IgG antibody responses to reimmunization varied according to pneumococcal serotype but in general were mediocre or poor; the poorest response was to serotype 6B. The antibody responses were similar in subjects with continued penicillin prophylaxis or placebo treatment, and in subjects who received one or two pneumococcal vaccinations before reimmunization. The occurrence of pneumococcal bacteremia was associated with low IgG antibody concentrations to the infecting serotype. CONCLUSIONS: Reimmunization of children with sickle cell anemia who received pneumococcal polysaccharide vaccine at age 5 years induces limited production of serotype-specific IgG antibodies, regardless of previous pneumococcal vaccine history. Continued penicillin prophylaxis does not interfere with serotype-specific IgG antibody responses to reimmunization. (J Pediatr 1996;129:828-35)

Objective : To evaluate the consequences of discontinuing penicillin prophylaxis at 5 years of age in children with sickle cell anemia who had received prophylactic penicillin for much of their lives. Design : Randomized, double-blind, placebo-controlled trial. Setting : Eighteen teaching hospitals throughout the United States. Patients : Children with sickle cell anemia (hemoglobin SS or hemoglobin S β 0 -thalassemia) who had received prophylactic penicillin therapy for at least 2 years immediately before their fifth birthday and had received the 23-valent pneumococcal vaccine between 2 and 3 years of age and again at the time of randomization. Of 599 potential candidates, 400 were randomly selected and followed for an average of 3.2 years. Interventions : After randomization, patients received the study medication twice daily-either penicillin V potassium, 250 mg, or an identical placebo tablet. Patients were either seen in the clinic or contacted every 3 months thereafter for an interval history and dispensing of the study drug. A physical examination was scheduled every 6 months. Main outcome measures : The primary end point was a comparison of the incidence of bacteremia or meningitis caused by Streptococcus pneumoniae in children continuing penicillin prophylaxis versus those receiving the placebo. Results : Six children had a systemic infection caused by S. pneumoniae , four in the placebo group (2.0%; 95% confidence interval 0.5%, 5.0%) and two in the continued penicillin prophylaxis group (1.0%; 95% confidence interval 0.1%, 3.6%), with a relative risk of 0.5 (95% confidence interval 0.1, 2.7). All invasive isolates were either serotype 6(A or B) or serotype 23F. Four of the isolates were penicillin susceptible, and two (one from each treatment group) were penicillin and multiply antibiotic resistant. Adverse effects of the study drug were reported for three patients (nausea, vomiting, or both), one of whom was in the placebo group. Conclusion : Children with sickle cell anemia who have not had a prior severe pneumococcal infection or a splenectomy and are receiving comprehensive care may safely stop prophylactic penicillin therapy at 5 years of age. Parents must be aggressively counseled to seek medical attention for all febrile events in children with sickle cell anemia. (J PEDIATR 1995;127:685-90)

Objective: We investigated the possibility that antimicrobial-resistant pneumococci were causing invasive disease in children with sickle-cell disease (SCD). Study design: Records of all children with SCD observed at the Mid-South Sickle Cell Center (MSSCC) at LeBonheur Children's Medical Center were reviewed from January 1990 to June 1994. Children with SCD and pneumococcal sepsis were identified. The Streptococcus pneumoniae isolates from these children were examined for serotype and antimicrobial susceptibilities. Two additional children not observed in the MSSCC had pneumococcal sepsis caused by penicillin-resistant isolates and were also included. Results: Antimicrobial susceptibility testing of the six penicillin-resistant isolates revealed that four were resistant to trimethoprim-sulfamethoxazole, two to erythromycin, and one to clindamycin. The two isolates that were resistant to ceftriaxone also were multiply resistant. From the MSSCC, 26 children had pneumococcal sepsis during the 4 1/2-year period studied. Five of these children (19%) died. Four (15%), including one who died, were infected with penicillin-resistant strains. Conclusion: Pneumococcal sepsis, meningitis, and infections of other foci in children with SCD may be caused by S. pneumoniae that is resistant to one or more antimicrobial agents, including penicillin. The addition of vancomycin to the antibiotics currently used for initial management should be considered in areas where the antibiotic resistance of S. pneumoniae is prevalent. (J PEDIATR 1995;127: 526-32)

Objective: To determine the effect of a transfusion program on risk of stroke recurrence in children with sickle cell disease. Design: The clinical course and experience with transfusion therapy at eight centers were reviewed for subjects whose initial stroke occurred after January 1988. Results: Sixty subjects were observed for 191.7 patient-years. Eight had a single recurrent stroke (two intracranial hemorrhages and six infarctions) for a prevalence of 13.3%, or one recurrence for each 24 patient-years of observation. Thirteen subjects had 15 transient neurologic events; two of these had subsequent strokes, but the overall risk was similar for those who did and those did not have transient events. Hemoglobin S levels were greater than the desired maximum of 30% at the time of 7 of 16 transient events and five of six recurrent infarctions. The stroke recurrence rate was similar to those in previous reports of children receiving long-term transfusion therapy but significantly less than that reported for children who did not receive transfusions ( p Conclusions: We conclude that maintenance of hemoglobin S at a level less than 30% appears to be effective in reducing the rate of recurrent infarction but does not prevent transient neurologic events. Transient neurologic events are common but do not appear to be related to recurrent stroke. (J P EDIATR 1995;126:896-9)

The disposition of recombinant human granulocyte colony-stimulating factor (G-CSF) was studied in 11 children with severe chronic neutropenia given 6 to 48 micrograms G-CSF per kilogram subcutaneously. Serum concentrations of G-CSF were measured by bioassay. Peak serum G-CSF concentrations were proportional to dosage and occurred 2 to 8 hours after subcutaneous administration. Nine of the eleven children had a significant increase in absolute neutrophil count (ANC). The median ANC in responding patients was 6.7 x 10(9)/L on day 14 versus 0.17 x 10(9)/L on day 1 of therapy (p0.01). The G-CSF clearance increased as ANC increased, and the relationship was well described by a sigmoid model. Maximal clearance approached 2 ml/min per kilogram at ANCs17.0 x 10(9)/L; minimal clearance was 0.29 ml/min per kilogram at ANCs of 0. The half-life of G-CSF was inversely related to ANC; mean half-life was 4.7 hours at ANCs of 0 but2 hours at ANCs greater than 17.0 x 10(9)/L. The two patients who failed to achieve a clinical response had no change in G-CSF clearance or half-life, nor did they have an increase in ANC when G-CSF dosages were escalated to 18 or 48 micrograms/kg twice a day. These results indicate that G-CSF pharmacokinetics are directly influenced by ANC; higher serum concentrations, slower clearances, and longer half-lives are associated with low ANCs.

Streptococcus pneumoniae sepsis is the most common invasive infection among patients with sickle cell disease. The risk of a recurrent episode of sepsis and subsequent death in those patients who have had a previous septic event is much higher. Patients with sickle disease who have had pneumococcal sepsis should continue penicillin prophylaxis indefinitely and should not be candidates for out-patient management of febrile episodes.

Objective: To obtain quantitative serum levels of total and ionized magnesium (Mg 2+ ) in children with homozygous sickle cell anemia (SCA) undergoing therapy with hydroxyurea. Study design: Five children, ages 11 to 14 years with homozygous SCA, were enrolled in a dose-escalating trial of hydroxyurea over an 18-month period. Serum levels of total and ionized magnesium together with ionized K + , Na + , and Ca 2+ were measured before hydroxyurea and every 6 months during hydroxyurea therapy. Results: Before treatment, 4 of the 5 patients had low or below-normal serum concentrations of Mg 2+ (normal range, 0.51-0.67 mmol/L). All 5 became Mg 2+ -deficient during hydroxyurea therapy, with no indication of recovery until after 12 to 18 months of drug administration ( P + , Na + , and Ca 2+ remained consistently within normal ranges. Conclusions: These findings warrant a controlled study of the effects of magnesium supplementation in patients with SCA receiving hydroxyurea. Potentially, such therapy could alleviate or prevent vaso-occlusive crises. (J Pediatr 2002;140:565-9)

Objectives: To compare the results of serial neuropsychologic testing in children with sickle cell disease with the results of serial magnetic resonance imaging (MRI) examinations, particularly to evaluate neuropsychologic function in the absence of overt stroke. Study design: In the Cooperative Study of Sickle Cell Disease, serial neuropsychologic and MRI tests were performed in 373 patients (255 with hemoglobin SS and 118 with hemoglobin SC), 6 to 18 years of age. MRI of the brain and a neuropsychologic battery that included the Wechsler Intelligence Scale for Children (WISC-R or WISC-III) and the Woodcock-Johnson Math and Reading Achievement Tests were performed concurrently and repeated every 2 to 3 years. A silent infarct was defined as an MRI finding of increased signal intensity on T 2 imaging in a patient without a history of stroke. Results: Twenty-seven patients, all with hemoglobin SS, had overt strokes and 62 had silent infarcts (52 with hemoglobin SS). Patients with hemoglobin SS and silent infarcts had significantly lower scores for math and reading achievement, Full-Scale IQ, Verbal IQ, and Performance IQ, when compared with those with normal MRI findings. In children with hemoglobin SS and normal MRI findings, the scores for Verbal IQ, math achievement, and coding (a subscale of Performance IQ) declined with increasing age. Conclusions: School-aged children with sickle cell disease had compromised neuropsychologic function in the presence of silent infarcts. In addition, they had declines in performance in certain areas of function over time. Therapeutic interventions that prevent or lessen cognitive impairment are needed before school entry for children with sickle cell disease. (J Pediatr 2001;139:391-7)

Objective: To determine whether abnormalities of the CNS are present in very young children with sickle cell anemia. Study design: Thirty-nine children with hemoglobin SS between the ages of 7 and 48 months were examined with magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA). No child had a history of clinical stroke, although 3 had a history of seizures (2 neonatal). Twenty-one patients underwent developmental testing with the Bayley or McCarthy Scales. Results: The overall prevalence of CNS abnormalities in asymptomatic children was 4 of 36 (11%, confidence interval 3, 26%). One patient had a silent infarct observed on MRI and a stenotic lesion on MRA; 3 other patients had stenotic lesions on MRA. The 3 patients who had a history of seizures all had lesions consistent with infarcts on MRI. Of the asymptomatic patients who had psychometric testing, 1 of 18 was developmentally delayed. One of 3 with a history of seizures had mild developmental delay. Conclusions: Very young children with sickle cell anemia (and no history of clinical stroke) have infarction in the brain and/or stenosis of major cerebral arteries, similar to those reported in older children. These findings indicate a need for larger studies to define the incidence of CNS lesions in this age group and to determine the need for early therapeutic intervention to prevent CNS sequelae of sickle cell disease. (J Pediatr 1998;132:994-8.)

We retrospectively examined the medical and autopsy records of seven previously unpublished cases of fatal pneumococcal septicemia in children with hemoglobin SC disease. The earliest death occurred in a 1-year-old child who had congenital heart disease with cyanosis; the other children were aged 3 1/2 to 15 years. Only one child had received pneumococcal vaccine or prophylactic penicillin therapy. All seven children had an acute febrile illness and rapid clinical deterioration despite parenterally administered antibiotic therapy and intensive medical support. Erythrocyte pit counts in two patients were 40.3% and 41.7%, respectively (normal,or = 3.6%). Autopsy data from five cases showed marked splenic congestion without infarction in five, splenomegaly in four, and bilateral adrenal hemorrhage in three. These cases illustrate that functional asplenia predisposes some children with hemoglobin SC disease to the development of fatal septicemia after the age of 3 years. We conclude that pneumococcal vaccine should be administered to all children with hemoglobin SC disease and that acute febrile illnesses should be investigated promptly for the possibility of septicemia. The routine use of prophylactic penicillin therapy in infants and children with hemoglobin SC disease remains controversial.

BABY HUG is an NHLBI/NICHD-sponsored Phase III randomized double-blinded placebo-controlled clinical trial (NCT00006400) to test the hypothesis that hydroxyurea can prevent chronic organ damage in very young children with sickle cell anemia (SCA). Renal and splenic function measures are the co-primary endpoints. Renal disease in SCA begins early in life with impaired urine concentration and acidification, along with glomerular hyperfiltration; some patients will progress to microalbuminuria, glomerulosclerosis, macroalbuminuria, and even renal failure. In BABY HUG, glomerular filtration rate (GFR) elevation was selected as a primary endpoint, to be measured quantitatively by plasma clearance of injected 99mTc-DTPA and also estimated by the Schwartz equation where GFR = (height × 0.55)/(serum creatinine), with creatinine measured by HPLC to .01 mg/dL precision. Of 233 enrolled subjects, 193 completed screening and were randomized to study treatment. Quantitative GFR measurement was successful in most cases: 176 of 182 (97%) of DTPA clearance studies were adequate and 157 subjects had both baseline DTPA and Schwartz GFR values available for analysis. The average age at GFR measurement was 13.7 ± 2.6 months (range 9–19 months) and 59% of subjects were female. Baseline mean (± 1SD) hematological parameters included hemoglobin = 9.0 ± 1.4 gm/dL, absolute reticulocytes = 295.3 ± 137.4 × 109/L, WBC = 14.3 ± 5.8 × 109/L, and fetal hemoglobin (HbF) = 25.6 ± 8.8%. Baseline past medical history included dactylitis (34%), splenic sequestration (7%), and acute chest syndrome (5%). The average baseline quantitative GFR measurement determined by DTPA clearance was elevated at 125.4 ± 34.4 mL/min/1.73m2, (range 40.2 – 300.9 mL/min/1.73m2, normal value 100 ± 20 mL/min/1.73m2). The average baseline GFR estimate by Schwartz equation was substantially higher at 193.9 ± 53.8 mL/min/1.73m2, range 65.8 – 350.0 mL/min/1.73m2. In univariate analysis, the DTPA GFR value was positively correlated with the Schwartz GFR estimate (r=0.22, p=0.0059, slope=0.145) as well as age, weight, height (all p≤.001) but not with hemoglobin, HbF, WBC, reticulocytes, previous sickle cell-related events, or measures of splenic function including liver-spleen scan and quantitation of pitted erythrocytes and micronuclei. The Schwartz GFR estimate was positively correlated with age, height, WBC, and splenic function, and negatively correlated with hemoglobin and HbF. Using a quantitative GFR threshold of 120 mL/min/1.73m2 and an age threshold of 15 months, higher GFR values were observed in older infants, p=0.026. These data indicate that renal dysfunction measured by GFR elevation may begin early in life in SCA; quantitative GFR measurement is feasible but highly variable in this very young patient population; (3) the Schwartz and DTPA GFR values are strongly correlated, but the Schwartz estimate is usually greater and only modestly agrees with the quantitative DTPA GFR value. These baseline GFR measurements in BABY HUG support the hypothesis of age- and disease-related glomerular hyperfiltration in SCA. BABY HUG should yield important information regarding the ability of hydroxyurea to prevent renal damage among infants with SCA.

Although long-term transfusion therapy is at least 90% effective in preventing recurrent strokes after an initial cerebrovascular accident in patients with sickle cell disease, it is unknown how long transfusion therapy should be continued. To address this question, we prospectively discontinued transfusions in 10 patients with sickle cell disease whose median duration of transfusion therapy after an initial stroke was 9 1/2 years (range 5 to 12 years). Before the transfusions were discontinued, patients were examined by cerebral angiography, magnetic resonance imaging of the head, neuropsychologic testing, electroencephalography, and a complete neurologic examination. Within 12 months after transfusion therapy was stopped, 5 of 10 patients had had an ischemic event. Three events caused relatively mild deficits in the same areas as those originally affected. Two were associated with massive intracranial hemorrhage, including one on the contralateral side of original involvement. An additional patient died suddenly of unknown causes. Of the four remaining patients, three declined to resume transfusion and are relatively well at greater than or equal to 18 months after therapy was stopped. The studies performed before transfusions were stopped were not predictive of recurrent stroke. The risk of recurrent cerebrovascular accident in this group was significantly greater than the estimated risk of 10% in patients who are receiving long-term transfusion therapy (p = 0.002). This adverse outcome suggests that patients with sickle cell disease who have had a stroke must receive long-term transfusion indefinitely or a suitable therapeutic alternative must be devised.

Les 20 bebes sont âges de 2 a 6 mois lors de la 1ere injection et en recoivent 3 a 2 mois d'intervalles; 13 sont HG-SS, 6 HG SC et 1 HG S-β thalassemie. Les resultats demontrent la haute immunogenicite du vaccin des l'âge de 2 mois. Reactions secondaires minimes

Erythrocyte properties of patients with congenital hypoplastic anemia were compared to those of patients with transient erythroblastopenia of childhood. The MCV was less than 85 in all nine TEC patients studied and greater than 90 in all 11 CHA patients. Hemoglobin F concentration was elevated beyond the normal level for age in eight CHA patients and almost always normal in TEC. The i antigen score was more likely to be elevated in CHA than in TEC. The activities of transaminase, aldolase, phosphofructokinase, and glutathione peroxidase were higher in CHA than in TEC (p less than 0.001). Some abnormal properties (namely, MCV and hemoglobi n F concentration) of CHA erythrocytes, present during remission but accentuated during relapse, seemed to vary with changes in serum erythropoietin. Early differentiation of TEC and CHA appears feasible, allowing prompt provision of a favorable prognosis and the avoidance of unnecessary corticosteroid therapy in TEC.

The combination of idiopathic thrombocytopenic purpura and autoimmune hemolytic anemia is rare in childhood. Among 164 instances of ITP and 15 instances of AHA, 11 patients were found to have this combination. Three were found to have systemic lupus erythematosus, one had aplastic anemia, and seven had Evans syndrome. Neutropenia, at times associated with bacterial infections, occurred in four of the latter patients. Unlike most cases of ITP or AHA in childhood, the clinical course of Evans syndrome is usually chronic and relapsing. Treatment including corticosteroids, splenectomy, and immunosuppressive agents has been generally unsatisfactory. In view of the frequent presence of antibodies directed at red blood cells, platelets, neutrophils, and lymphocytes, immunopancytopenia may be a better term for this condition.

Non-transferrin-bound iron (NTBI), a potentially toxic compound, is increased in the serum of patients with iron overload and fully saturated transferrin. We found markedly elevated NTBI levels in 16 children (including nine with sickle cell disease and five with beta-thalassemia) with iron overload secondary to prolonged transfusion therapy. During iron chelation with subcutaneous desferrioxamine infusion, NTBI levels decreased to normal, but became elevated within 2 to 4 hours after discontinuation of desferrioxamine. NTBI causes hepatic and cardiac toxicity in experimental systems, but our patients lacked sufficient organ dysfunction for this association to be made. The use of continuous 24-hour chelation to maintain NTBI at low levels may prevent progressive iron toxicity in patients who first received chelation therapy at an older age or who already have evidence of cardiac damage.