Acute Splenic Sequestration in a 2-Month-Old Infant With Sickle Cell Anemia

Acute splenic sequestration crisis is a potentially fatal complication of sickle cell anemia. It is characterized by acute splenic enlargement, with trapping of erythrocytes, causing increasing anemia and the potential for circulatory failure. The development of newborn screening programs aimed at identifying children with clinically significant hemoglobinopathies, combined with early parental education and careful follow-up, has decreased the overall mortality due to acute splenic sequestration crisis and other complications during the early years of life. The purpose of this paper is to report the case of an 8-week-old infant with sickle cell anemia and acute splenic sequestration crisis.

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Newborn Screening for Sickle Cell Disease: Effect on Mortality

PEDIATRICS ◽

10.1542/peds.81.6.749 ◽

1988 ◽

Vol 81 (6) ◽

pp. 749-755

Author(s):

Elliott Vichinsky ◽

Deborah Hurst ◽

Ann Earles ◽

Klara Kleman ◽

Bertram Lubin

Keyword(s):

Sickle Cell Disease ◽

Mortality Rate ◽

Newborn Screening ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Comprehensive Treatment ◽

Cell Disease ◽

Hemoglobin S ◽

Screening Programs ◽

Overall Mortality

Newborn screening for sickle cell disease has been recommended as a method of decreasing patient mortality. However, its effectiveness in accomplishing this has not been reliably measured. To help determine the effectiveness, 10 years of experience in newborn screening have been summarized. The effects of early patient enrollment in a comprehensive treatment program on long-term morbidity and mortality are reported. From 1975 to 1985, 84,663 newborns were screened regardless of race or ethnic background. Bart's hemoglobin was present in 5%, hemoglobin AS in 2.6%, and hemoglobin AC in 0.75%. Excluding Bart's, approximately 3.6% of all newborns were carriers for hemoglobinopathy. Sickle cell disease occurred in 1:951 births (58 hemoglobin SS, 25 hemoglobin FSC, three hemoglobin S-β+-thalassemia, and three hemoglobin S-β°-thalassemia). In addition, one in every 4,233 newborns had a clinically significant thalassemia syndrome (eight hemoglobin FE, ten hemoglobin F only, two hemoglobin H). Compared with other newborn screening programs in California, (congenital hypothyroidism, 1:3,849; phenylketonuria 1:22,474, galactosemia 1:74,103), hemoglobinopathies are the most prevalent congenital disease. Eighty-one newborns with sickle cell disease were followed for 7.2 years. Patients experienced 513 hospitalizations, including 13 episodes of sepsis with or without meningitis and ten acute sequestration crises. The overall mortality rate for patients with sickle cell anemia diagnosed in the newborn period was 1.8%. In comparison, the clinical course of 64 patients with sickle cell anemia diagnosed after 3 months of age and followed for an average of 9.4 years was analyzed. Five of these patients died. In two of these, sickle cell anemia was diagnosed at the time of the death. Overall mortality rate in this group was 8%. In summary, the data indicate that newborn screening, when coupled with extensive follow-up and education, will significantly decrease patient mortality.

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Newborn Screening for Sickle Cell Disease: Effect on Mortality

PEDIATRICS ◽

10.1542/peds.83.5.834 ◽

1989 ◽

Vol 83 (5) ◽

pp. 834-834

Author(s):

Elliott Vichinsky ◽

Deborah Hurst ◽

Ann Earles ◽

Klara Kleman ◽

Bertram Lubin

Keyword(s):

Sickle Cell Disease ◽

Mortality Rate ◽

Newborn Screening ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Comprehensive Treatment ◽

Cell Disease ◽

Screening Programs ◽

Hb S ◽

Overall Mortality

Newborn screening for sickle cell disease has been recommended as a method of decreasing patient mortality. However, its effectiveness in accomplishing this has not been reliably measured. To help determine the effectiveness, 10 years of experience in newborn screening have been summarized. The effects of early patient enrollment in a comprehensive treatment program on long-term morbidity and mortality are reported. From 1975 to 1985, 84,663 newborns were screened regardless of race or ethnic background. Hb Bait's was present in 5%, hemoglobin AS in 2.6%, and hemoglobin AC in 0.75%. Excluding Bart's, approximately 3.6% of all newborns were carriers for hemoglobinopathy. Sickle cell disease occurred in 1:951 births (58 Hb 55, 25 Hb FSC, three Hb S-β+-thalassemia, and three Hb S-β°-thalassemia). In addition, one in every 4,233 newborns had a clinically significant thalassemia syndrome (eight Hb FE, ten Hb F only, two Hb H). Compared with other newborn screening programs in California (congenital hypothyroidism, 1:3,849; phenylketonuria, 1:22,474; galactosemia, 1:74,103), hemoglobinopathies are the most prevalent congenital disease. Eighty-one newborns with sickle cell disease were followed up for 7.2 years. Patients experienced 513 hospitalizations, including 13 episodes of sepsis with or without meningitis and ten acute sequestration crises. The overall mortality rate for patients with sickle cell anemia diagnosed in the newborn period was 1.8%. In comparison, the clinical course of 64 patients with sickle cell anemia diagnosed after 3 months of age and followed up for an average of 9.4 years was analyzed. Five of these patients died. In two of these, sickle cell anemia was diagnosed at the time of the death. Overall mortality rate in this group was 8%. In summary, the data indicate that newborn screening, when coupled with extensive follow-up and education, will significantly decrease patient mortality.

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Northern California's Experience

PEDIATRICS ◽

10.1542/peds.83.5.868 ◽

1989 ◽

Vol 83 (5) ◽

pp. 868-871

Author(s):

Deborah Hurst

Keyword(s):

Sickle Cell ◽

Health Care Professionals ◽

Public Information ◽

Prenatal Testing ◽

Early Years ◽

Educational Outreach ◽

Screening Programs ◽

Optimal Screening ◽

The Difference

Future plans involve continued expansion of cord blood screening in the Bay Area until no babies with hemoglobin diseases are missed. Modification of screening and trait follow-up procedures will continue as necessary to allow screening of increased numbers despite limitations in funding. To reduce the need for intensive trait follow-up by the center, we will continue to develop community resources. There must be more general public information about hemoglobin traits, more well-run prenatal testing and counseling programs, and continued education of health care professionals. It is also essential to assess the effect of hemoglobin trait notification on the involved families. A definitive trait follow-up study could help state public health departments design optimal screening programs that provide satisfactory trait follow-up without detrimental psychologic effects or prohibitive expense. Historical studies of the effects of trait screening at other times or in other ethnic groups for different diseases may not be applicable to our population. For example, in trait follow-up today, initial parental anxiety when notified of an abnormal blood test in the baby more often involves fear of acquired immunodeficiency syndrome than fear of sickle cell disease. Most people now can be reassured about the difference between trait and disease and about the fact that their baby with trait is healthy. Clearly, the level of public knowledge has increased since the early years of screening because of the sickle cell center's educational outreach as well as general exposure to information on television and in public school curricula. These impressions should be documented by studies to assess the levels of understanding and anxiety in families before and after counseling. In addition, information concerning the 17% of individuals who make appointments but never appear for counseling and the 28% who are not contacted by either telephone or mail would be useful. There is no way of knowing how many of these people simply do not need or want counseling, how many never receive the information, and how many avoid further contact because of inappropriate anxiety. Tracking these individuals would be a major undertaking, beyond the scope of current staffing, but an important future study.

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Ischemic Stroke in Children and Young Adults with Sickle Cell Disease (SCD) in the Post-STOP Era

Blood ◽

10.1182/blood.v126.23.68.68 ◽

2015 ◽

Vol 126 (23) ◽

pp. 68-68 ◽

Cited By ~ 3

Author(s):

Janet L. Kwiatkowski ◽

Julie Kanter ◽

Heather J. Fullerton ◽

Jenifer Voeks ◽

Ellen Debenham ◽

...

Keyword(s):

Ischemic Stroke ◽

High Risk ◽

Sickle Cell Disease ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Stroke Prevention ◽

Cell Disease ◽

Clinical Series ◽

The Mean

Abstract Background: The Stroke Prevention Trial in Sickle Cell Anemia (STOP) and Optimizing Primary Stroke Prevention in Sickle Cell Anemia (STOP 2) established routine transcranial Doppler ultrasound (TCD) screening with indefinite chronic red cell transfusions (CRCT) for children with abnormal TCD as standard of care. To identify children at high-risk of stroke, annual TCD screening is recommended from ages 2 to 16 years, with more frequent monitoring if the result is not normal. A reduction in stroke incidence in children with SCD has been reported in several clinical series and analyses utilizing large hospital databases when comparing rates before and after the publication of the STOP study in 1998. We sought to determine the rate of first ischemic stroke in a multicenter cohort of children who had previously participated in the STOP and/or STOP 2 trials and to determine whether these strokes were screening or treatment failures. Subjects and Methods: Between 1995 and 2005, STOP and STOP 2 (STOP/2) were conducted at 26 sites in the US and Canada. These studies included 3,835 children, ages 2 to 16 y with SCD type SS or S-beta-0-thalassemia. Participation in STOP/2 ranged from a single screening TCD to randomization. STOP 2 also had an observational arm for children on CRCT for abnormal TCD whose TCD had not reverted to normal. The Post-STOP study was designed to follow-up the outcomes of children who participated in one or both trials. 19 of the 26 original study sites participated in Post-STOP, contributing a total of 3,539 (92%) of the STOP/2 subjects. After exit from STOP/2, these children received TCD screening and treatment according to local practices. Data abstractors visited each clinical site and obtained retrospective data from STOP/2 study exit to 2012-2014 (depending on site) including follow-up TCD and brain imaging results, clinical information, and laboratory results. Two vascular neurologists, blinded to STOP/2 status and prior TCD and neuroimaging results, reviewed source records to confirm all ischemic strokes, defined as a symptomatic cerebral infarction; discordant opinions were resolved through discussion. For the first Post-STOP ischemic stroke, prior TCD result and treatment history subsequently were analyzed. Results: Of the 3,539 subjects, follow-up data were available for 2,850 (81%). Twelve children who had a stroke during STOP or STOP2 were excluded from these analyses resulting in data on 2,838 subjects. The mean age at the start of Post-STOP was 10.5 y and mean duration of follow-up after exiting STOP/2 was 9.1 y. A total of 69 first ischemic strokes occurred in the Post-STOP observation period (incidence 0.27 per 100 pt years). The mean age at time of stroke was 14.4±6.2 (median 13.8, range 3.5-28.9) y. Twenty-five of the 69 patients (36%) had documented abnormal TCD (STOP/2 or Post-STOP) prior to the stroke; 15 (60%) were receiving CRCT and 9 (36%) were not (treatment data not available for 1 subject). Among the 44 subjects without documented abnormal TCD, 29 (66%) had not had TCD re-screen in the Post-STOP period prior to the event; 7 of these 29 (24%) were 16 y or older at the start of Post-STOP, which is beyond the recommended screening age. Four of the 44 (9%) patients had inadequate TCD in Post-STOP (1 to 10.7 y prior to event). Six (14%) had normal TCD more than a year before the event (1.2 - 4 y); all but one of these children were younger than 16 y at the time of that TCD. Only 5 (11%) had a documented normal TCD less than 1 year prior to the event. Conclusions: In the Post-STOP era, the rate of first ischemic stroke was substantially lower than that reported in the Cooperative Study of Sickle Cell Disease, prior to implementation of TCD screening. Many (39%) of the Post-STOP ischemic strokes were associated with a failure to re-screen according to current guidelines, while only 11% occurred in children who had had recent low-risk TCD. Among those known to be at high risk prior to stroke, treatment refusal or inadequate treatment may have contributed. While TCD screening and treatment are effective at reducing ischemic stroke in clinical practice, significant gaps in screening and treatment, even at sites experienced in the STOP protocol, remain to be addressed. Closing these gaps should provide yet further reduction of ischemic stroke in SCD. Disclosures No relevant conflicts of interest to declare.

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HMOX1 and Acute Kidney Injury in Sickle Cell Anemia

Blood ◽

10.1182/blood.v130.suppl_1.686.686 ◽

2017 ◽

Vol 130 (Suppl_1) ◽

pp. 686-686

Author(s):

Santosh L. Saraf ◽

Maya Viner ◽

Ariel Rischall ◽

Binal Shah ◽

Xu Zhang ◽

...

Keyword(s):

Chronic Kidney Disease ◽

Acute Kidney Injury ◽

Risk Factor ◽

Kidney Disease ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Kidney Injury ◽

Ckd Progression ◽

Kdigo Guidelines

Abstract Acute kidney injury (AKI) is associated with tubulointerstitial fibrosis and nephron loss and may lead to an increased risk for subsequently developing chronic kidney disease (CKD). In adults with sickle cell anemia (SCA), high rates of CKD have been consistently observed, although the incidence and risk factors for AKI are less clear. We evaluated the incidence of AKI, defined according to Kidney Disease Improving Global Outcomes (KDIGO) guidelines as a rise in serum creatinine by ≥0.3mg/dL within 48 hours or ≥1.5 times baseline within seven days, in 158 of 299 adult SCA patients enrolled in a longitudinal cohort from the University of Illinois at Chicago. These patients were selected based on the availability of genotyping for α-thalassemia, BCL11A rs1427407, APOL1 G1/G2, and the HMOX1 rs743811 and GT-repeat variants. Median values and interquartile range (IQR) are provided. With a median follow up time of 66 months (IQR, 51-74 months), 137 AKI events were observed in 63 (40%) SCA patients. AKI was most commonly observed in the following settings: acute chest syndrome (25%), an uncomplicated vaso-occlusive crisis (VOC)(24%), a VOC with pre-renal azotemia determined by a fractional excretion of sodium <1% or BUN-to-creatinine ratio >20:1 (14%), or a VOC with increased hemolysis, defined as an increase in serum LDH or indirect bilirubin level >1.5 times over the baseline value at the time of enrollment (12%). Compared to individuals who did not develop AKI, SCA adults who developed an AKI event were older (AKI: median and IQR age of 35 (26-46) years, no AKI: 28 (23 - 26) years; P=0.01) and had a lower estimated glomerular filtration rate (eGFR) (AKI: median and IQR eGFR of 123 (88-150) mL/min/1.73m2, no AKI: 141 (118-154) mL/min/1.73m2; P=0.02) by the Kruskal-Wallis test at the time of enrollment. We evaluated the association of a panel of candidate gene variants with the risk of developing an AKI event. These included loci related to the degree of hemolysis (α-thalassemia, BCL11A rs1427407), to chronic kidney disease (APOL1 G1/G2 risk variants), and to heme metabolism (HMOX1) . Using a logistic regression model that adjusted for age and eGFR at the time of enrollment, the risk of an AKI event was associated with older age (10-year OR 2.6, 95%CI 1.4-4.8, P=0.002), HMOX1 rs743811 (OR 3.1, 95%CI 1.1-8.7, P=0.03), and long HMOX1 GT-repeats, defined as >25 repeats (OR 2.5, 95%CI 1.01-6.1, P=0.04). Next, we assessed whether AKI is associated with a more rapid decline in eGFR and with CKD progression, defined as a 50% reduction in eGFR, on longitudinal follow up. Using a mixed effects model that adjusted for age and eGFR at the time of enrollment, the rate of eGFR decline was significantly greater in those with an AKI event (β = -0.51) vs. no AKI event (β = -0.16) (P=0.03). With a median follow up time of 66 months (IQR, 51-74 months), CKD progression was observed in 21% (13/61) of SCA patients with an AKI event versus 9% (8/88) without an AKI event. After adjusting for age and eGFR at the time of enrollment, the severity of an AKI event according to KDIGO guidelines (stage 1 if serum creatinine rises 1.5-1.9 times baseline, stage 2 if the rise is 2.0-2.9 times baseline, and stage 3 if the rise is ≥3 times baseline or ≥4.0 mg/dL or requires renal replacement therapy) was a risk factor for CKD progression (unadjusted HR 1.6, 95%CI 1.1-2.3, P=0.02; age- and eGFR-adjusted HR 1.6, 95%CI 1.1-2.5, P=0.03). In conclusion, AKI is commonly observed in adults with sickle cell anemia and is associated with increasing age and the HMOX1 GT-repeat and rs743811 polymorphisms. Furthermore, AKI may be associated with a steeper decline in kidney function and more severe AKI events may be a risk factor for subsequent CKD progression in SCA. Future studies understanding the mechanisms, consequences of AKI on long-term kidney function, and therapies to prevent AKI in SCA are warranted. Disclosures Gordeuk: Emmaus Life Sciences: Consultancy.

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Splenomegaly in Children with Sickle Cell Anemia Receiving Hydroxyurea in Sub-Saharan Africa

Blood ◽

10.1182/blood-2019-129937 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 993-993

Author(s):

Leon Tshilolo ◽

George A. Tomlinson ◽

Patrick T. McGann ◽

Teresa S. Latham ◽

Peter Olupot-Olupot ◽

...

Keyword(s):

Board Of Directors ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Growth Parameters ◽

Sub Saharan Africa ◽

Advisory Committees ◽

Splenic Enlargement ◽

Hydroxyurea Treatment ◽

Lower Blood ◽

Sub Saharan

Introduction. Children with sickle cell anemia enrolled in Realizing Effectiveness Across Continents with Hydroxyurea (REACH, NCT01966731) received open-label hydroxyurea at maximum tolerated dose (MTD) in four countries within sub-Saharan Africa (Tshilolo et al, NEJM 2019;380:121-131). Unlike children in the United States or Europe, a substantial proportion of REACH participants had splenomegaly at enrollment, and more developed splenomegaly while receiving hydroxyurea. Splenic enlargement in association with hydroxyurea treatment in sub-Saharan Africa is previously unrecognized, and its causes and consequences remain unclear. Methods. Palpable splenomegaly was evaluated at both the mid-clavicular and mid-axillary lines at each scheduled and unscheduled sick visit. The size of the spleen, defined as the greatest distance (cm) below the subcostal margin, was recorded in the REDCap trial database at all four clinical sites. Cross-sectional analysis was performed at baseline enrollment using four spleen categories (Not Palpable, 1-4 cm, ≥5 cm, or Splenectomy) with correlations for age, sex, site, growth parameters, alpha-thalassemia trait and G6PD deficiency. This analysis was repeated using the largest spleen size over the first two years on hydroxyurea, but examining two-year laboratory values and also the hydroxyurea dose at MTD, time to MTD, dose-limiting toxicities, and clinical outcomes including acute splenic sequestration, malaria infections, and sepsis. Results. A total of 606 children started hydroxyurea study treatment, including 6 (1.0%) with previous splenectomy, 59 (9.7%) with previous splenic sequestration, and 99 (16.3%) with palpable splenomegaly at enrollment (52 children with 1-4 cm and 47 with ≥5 cm). Large spleens (≥5 cm) were commonly observed at baseline at all clinical sites except Uganda, which identified only 1 child. Compared to those with no palpable spleen, children with large spleens at baseline had similar age and growth parameters, but were significantly more likely to have alpha-thalassemia (78.7% versus 56.2%, P=0.004) and also G6PD deficiency among males (28.0% versus 17.6%, P=0.32). Children with large spleens at enrollment also had a lower hemoglobin (Hb = 6.5 versus 7.3 g/dL, P<0.001) and lower platelet count (platelets = 227 versus 410 x 109/L, P<0.001), but equivalent fetal hemoglobin (HbF = 10.2 versus 9.4%, P=0.82). On hydroxyurea treatment with escalation to MTD, 262 children (43.7%) had palpable splenomegaly recorded, including 120 (20.0%) with spleens ≥5 cm. These large spleens were observed at all four clinical sites, with DRC having the most (52) and Uganda with the least (14). After 24 months of hydroxyurea treatment, laboratory differences were noted according to the cumulative occurrence of splenomegaly including a significantly lower hemoglobin and platelet count, higher absolute reticulocyte count, and lower hydroxyurea dose at MTD (Table). Large spleens were associated with a high cumulative incidence of laboratory dose-limiting toxicities, as well as a significantly higher risk of having clinically symptomatic malaria and receiving blood transfusions (Table). A total of 31 children (5.2%) on hydroxyurea treatment received elective splenectomy, including one partial splenectomy using arterial embolization. Conclusion. Children with sickle cell anemia living in sub-Saharan Africa have an increased risk of having palpable splenomegaly, which is further increased while receiving hydroxyurea treatment. Large spleen at baseline were associated with lower blood counts, consistent with hypersplenism. On hydroxyurea treatment, children with large spleens had significantly lower blood counts and more dose-limiting toxicities, which lowered their eventual hydroxyurea dose at MTD but still led to robust HbF responses. Children with large spleens were also at higher risk of developing malaria infections, receiving transfusions, and requiring surgical splenectomy. Splenic enlargement in association with hydroxyurea treatment was common in children with sickle cell anemia in the REACH trial; its cause remains unclear but the consequences include substantial laboratory toxicity and clinical morbidity. Investigating the etiologies and management of children with chronically enlarged spleens is crucial before expanding hydroxyurea access across Africa for sickle cell anemia. Disclosures Ware: Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Other: Research Drug Donation; 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; Agios: Membership on an entity's Board of Directors or advisory committees; Addmedica: Other: Research Drug Donation.

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Fatal Acute Splenic Sequestration at 4 Months of Age

PEDIATRICS ◽

10.1542/peds.73.4.507 ◽

1984 ◽

Vol 73 (4) ◽

pp. 507-508

Author(s):

Juan N. Walterspiel ◽

Joe C. Rutledge ◽

Bryan L. Bartlett

Keyword(s):

Cord Blood ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Screening Program ◽

Splenic Sequestration ◽

Blood Screening

A patient with homozygous sickle cell anemia is the youngest known to have died from acute splenic sequestration crisis. A cord blood screening program might have prevented this infant's death.

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Barriers to Pediatric Sickle Cell Disease Guideline Recommendations

Global Pediatric Health ◽

10.1177/2333794x19847026 ◽

2019 ◽

Vol 6 ◽

pp. 2333794X1984702 ◽

Cited By ~ 3

Author(s):

Michael D. Cabana ◽

Julie Kanter ◽

Anne M. Marsh ◽

Marsha J. Treadwell ◽

Michael Rowland ◽

...

Keyword(s):

Sickle Cell Disease ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Support Staff ◽

Cell Disease ◽

National Guidelines ◽

Convenience Sample ◽

Different Types ◽

Pediatric Sickle Cell Disease

National guidelines recommend that providers counsel all patients with sickle cell anemia about hydroxyurea (HU) therapy and screen children with sickle cell anemia annually for the risk of stroke with transcranial Doppler (TCD). We surveyed a national convenience sample of sickle cell disease clinicians to assess factors associated with low adherence. Adherence was 46% for TCD screening. Low adherence was associated with a lack of outcome expectancy (eg, a belief that there would be poor patient follow-up to TCD testing; P < .05). Adherence was 72% for HU counseling. Practice barriers (eg, lack of support staff or time) and a lack of agreement with HU recommendations were associated with low adherence ( P < .05). This study demonstrates that different types of strategies are needed to improve TCD screening (to address follow-up and access to testing) versus HU counseling (to address physician agreement and practice barriers).

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An objective sign in painful crisis in sickle cell anemia: the concomitant reduction of high density red cells

Blood ◽

10.1182/blood.v64.2.559.559 ◽

1984 ◽

Vol 64 (2) ◽

pp. 559-563 ◽

Cited By ~ 45

Author(s):

ME Fabry ◽

L Benjamin ◽

C Lawrence ◽

RL Nagel

Keyword(s):

Sickle Cell ◽

Sickle Cell Anemia ◽

State Level ◽

Red Cells ◽

Average Decrease ◽

Concomitant Reduction ◽

Objective Sign ◽

The Stability ◽

Painful Crisis

Abstract The etiopathologic basis of painful crisis in sickle cell anemia is largely unknown, and no objective criteria for its diagnosis and follow- up exist at present. We have studied 11 patients through 14 painful crises and observed a significant decrease of the densest fraction of red cells in 12 of the 14 crises as determined by isopycnic Percoll- Stractan continuous density gradients. If the first observation is normalized to 100%, the average decrease in dense cells was 77% with a range of 36% to 94%. The time needed for the percentage of dense cells to return to the steady-state level varied from seven to more than 30 days. These findings were in sharp contrast to the stability of the density pattern observed in another group of sickle cell patients, who were studied during crisis-free periods. The mechanism of the disappearance of dense cells could involve selective destruction by the reticuloendothelial (RE) system, selective sequestration in the areas of vasoocclusion, or a combination of both factors.

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