The chronic hemolytic anemia of SCD presents with mild to moderately low Hb and hematocrit (Hct) levels and a reticulocytosis of approximately 3% to 15%. Additional laboratory features of hemolysis include unconjugated hyperbilirubinemia with relative elevations of both indirect (unconjugated) and total bilirubin, elevated lactate dehydrogenase (LDH), and low to absent haptoglobin levels. During vaso-occlusive episodes (VOEs), hemolytic laboratory parameters may become more pronounced with significant elevations in bilirubin, LDH, and reticulocyte counts above steady-state levels in addition to worsening of anemia. Baseline compensatory reticulocytosis in the setting of chronic hemolysis accounts for high or high-normal mean corpuscular volume (MCV). If the age-adjusted MCV is not elevated, the possibility of sickle cell– β -thalassemia, coincident α -thalassemia, or iron deficiency must be considered in the diagnostic work up.

In the peripheral smear (Fig. 1), there may be sickled RBC forms, target cells, polychromasia indicative of reticulocytosis, and Howell-Jolly bodies in the setting of functional hyposplenia or asplenia. RBCs are typically normochromic unless there is coexistent thalassemia or iron deficiency. Sickled forms (irreversibly sickled cells [ISCs]) occur in the peripheral smear only in SCD and not in sickle cell trait. In HbSS disease, ISCs predominate, and target cells may be few; in HbSC disease, target cells predominate, and ISCs are rare; in sickle cell– β -thalassemia, ISCs, target cells, and hypochromic micro cyticdiscocytes are prominent.

Fig1. SICKLE CELL DISEASE AND HEMOGLOBIN SC PERIPHERAL BLOOD SMEARS. The peripheral smear in sickle cell disease (A) shows sickle cells that are mostly irreversibly sickled and sometimes referred to as “cigar forms.” Higher power detail (B) shows a sickle cell (upper left), red blood cell containing a Howell-Jolly body (middle right), and polychromatophilic cell (lower center). These indicate sickle cell anemia and splenic dysfunction but marrow response with reticulocytosis, respectively. A peripheral smear of a patient with HbSC (C) shows no sickled cell, but there are target forms (D) and occasional cells (E) with hemoglobin condensed at each pole of the cell.

White blood cell (WBC) counts are higher than normal in HbSS and HbS β 0-thalassemia disease, particularly in patients under age 10 years. Mean WBC counts tend not to be elevated in HbSC disease or HbS β +-thalassemia. Mean platelet counts are elevated in SCA, par ticularly in patients younger than age 18 years, but are usually normal in those with HbSC disease and HbS β +-thalassemia.

Solubility Tests and Hemoglobin Electrophoresis

Solubility test results (e.g., Sickledex) are positive in both SCD and sickle cell trait. All patients require definitive diagnosis with Hb electrophoresis (which separates Hb species according to amino acid composition) (Fig. 2) or high-performance liquid chromatography (HPLC). Cellulose acetate electrophoresis at a pH of 8.4 is a standard method of separating HbS from other variants. However, HbS, G, and D have the same electrophoretic mobility with this method. Using citrate agar electrophoresis at pH 6.2, HbS has a different mobility than HbD and HbG, which comigrate with HbA in this system.

Fig2. COMPARATIVE ANALYSES OF SEVERAL MUTANT HEMOGLOBINS USING ALKALINE ELECTROPHORESIS, ACID ELECTROPHORESIS, AND THIN-LAYER ISOELECTRIC FOCUSING. On the right are shown the components of the standard (top) and the phenotypes of the other six samples. Their analyses are shown by alkaline hemoglobin electrophoresis in the left panel, acid electrophoresis in the center panel, and thin-layer isoelectric focusing in the right panel. Locations of the various hemoglobin bands are shown below the left and center panels. A, Hemoglobin A; A2, hemoglobin A2; C, hemoglobin C; E, hemoglobin E; F, hemoglobin F; S, hemoglobin S. (Courtesy M. H. Steinberg.)

Results from electrophoresis or thin-layer isoelectric focusing are similar in HbSS disease and HbS β 0-thalassemia: nearly all of the Hb consists of HbS. Although differences in the HbF (see Variant Sickle Cell Syndromes) and HbA 2 levels may be useful in distinguishing these syndromes, the presence of microcytosis of one parent without sickle cell trait is a more useful indicator of HbS β 0-thalassemia or HbS– β +-thalassemia. The diagnosis of HbSC disease is straightfor ward; nearly equal amounts of HbS and HbC are detected. HbS β +- thalassemia and sickle cell trait both have substantial amounts of HbA and HbS; whereas sickle cell trait is associated with neither ane mia nor microcytosis and has an HbA fraction more than 50%,  sickle cell– β +-thalassemia is associated with anemia, microcytosis, and an HbA fraction less than HbS, ranging from 5% to 30%.

Coinheritance of alpha-thalassemia (silent carrier or trait) is difficult to ascertain from standard hematology and requires DNA sequencing of the alpha-globin gene which can be performed as a send out test to specialized laboratories.

The HbF level is usually slightly to moderately elevated although there is significant variability among patients. The amount of HbF present is a function of the number of reticulocytes that contain HbF, the extent of selective survival of HbF-containing reticulocytes that become mature HbF-containing erythrocytes (F cells), the amount of HbF per F cell, and co-inheritance of HbF genetic variants, includ ing the β S-haplotypes.  The Arab–Indian and Senegal haplotypes are associated with higher levels of HbF than the others. HbF is also influenced by SCD-directed therapies, specifically hydroxyurea (HU), which will be discussed later in this chapter.

Newborn Screening

The use of prophylactic penicillin 27 and the provision of comprehensive medical care during the first 5 years of life have reduced the mortality rate from approximately 25% to less than 3%, thereby underlining the importance of early identification of infants with SCD. Based on its economy and superiority of detection, universal screening of all newborns is preferred over ethnically targeted approaches. This screening approach was endorsed by a consensus panel convened by the National Institutes of Health. Since 2008, SCD screening in newborns is mandated in all 50 states of the US and the District of Columbia.  Blood samples for testing are obtained by heel stick and spotted onto filter paper for stable transport and subsequent HPLC. It should be noted that HPLC screening in very premature newborns can result in misdiagnosis given that the switch from fetal to adult Hb has not completed and the level of HbS may still be below the threshold for solubility testing and the results may not be valid.

As HbS increases and HbF declines in the first months of life (Fig. 3), the clinical manifestations of SCD, including anemia, emerge. ISCs can be seen on the peripheral blood smear (Fig. 4) of children with SCA at 3 months of age, and by 4 months of age, moderately severe hemolytic anemia is evident.

Fig3. FETAL HEMOGLOBIN DECLINE IN CHILDREN WITH HEMOGLOBINS AA AND SS. HbF, fetal hemoglobin. (Data from O’Brien, Mclatosh S, Aspnes AT, et al. Prospective study of sickle cell anemia in infancy. J Pediatr. 1976;89(2):205, 1976.)

Fig4. The peculiar elongated shapes of the erythrocytes is what Herrick ’s intern Ernest E. Irons noted, and together with a report from the German literature of sichel formen blood cells, inspired the name by which this condition is now known.

Tests used in newborn screening must be capable of distinguishing between HbF, S, A, and C. The Hb distribution pattern is described in descending order according to the quantities detected.

Therefore, a newborn with SCA who has predominantly HbF with a small amount of HbS and no HbA is described as having an FS pat tern. An FS pattern is obtained also in newborns who have HbSβ °- thalassemia, HbS–hereditary persistence of HbF (HPFH), and HbSD or HbSG (since HbD and HbG have the same electrophoretic mobility as HbS). A newborn with sickle cell trait will have HbF, HbA, and HbS ( FAS pattern). The quantity of HbA is greater than that of HbS. If the quantity of HbS exceeds that of HbA, the presumptive diagnosis is HbS/ β +-thalassemia (FSA pattern). It may not be possible to distinguish FAS and FSA patterns in newborns, so DNA-based testing or repeat Hb testing at age 3 to 6 months is recommended. Several alternative, point-of-care approaches are currently under development and a commercially available kit utilizing an antibody-based lateral-flow assay is marketed under the name of Sickle SCAN.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الفكريّة يُهدي إصداراته العلمية إلى مكتبات محافظة كركوك

شعبة فاطمة بنت أسد تطلق مسابقتها الإلكترونية (منارة الجود في مهد الصبا) لكتابة القصة للأطفال

المجمع العلمي يقيم برنامجًا قرآنيًا تعليميًا في النجف الأشرف

قسم الشؤون الدينية يقيم مجلسًا عزائيًّا لاستذكار أهل البيت (عليهم السلام)

المزيد

الآخبار الصحية

ما هي أفضل العصائر لصحة القلب وتقوية المناعة والنوم العميق؟

الأطعمة الغنية بالبروتينات النباتية تقلل خطر الأمراض المزمنة

وجع الأوتار قد يخفي خطرا صحيا مرتبطا بالقلب

أزمة "السفينة الموبوءة"..الأرجنتين تحقق في مصدر تفشي "هانتا"

المزيد

الآخبار التكنلوجية

باحثون يحددون تأثير القهوة على الميكروبيوم والمزاج

روسيا.. ابتكار تقنية لمعالجة سبائك التيتانيوم لحماية الطائرات والسيارات

بكين وواشنطن تدرسان إطلاق محادثات رسمية حول الذكاء الاصطناعي

لأول مرة في الولايات المتحدة.. تشغيل مفاعل مصغر نووي يغذي الذكاء الاصطناعي بالطاقة

المزيد

مواضيع ذات صلة

Laboratory Investigation of Hypothyroidism

Tests for Activity of Antimicrobial Combinations

Bactericidal Tests

Commercial Susceptibility Testing Systems

Conventional Testing Methods: Agar Dilution

Conventional Testing Methods: Broth Dilution

Laboratory Diagnosis of Autoimmune Hemolytic Anemia

Blood Coagulation Tests

Western Blot Immunoassays

Indirect Fluorescent Antibody Tests and Other Immunomicroscopic Methods

Enzyme-Linked Immunosorbent Assays

Laboratory Diagnosis of Thyrotoxicosis