Site of Binding of Chromium-51 to Hæmoglobin

The Sickle Effect: The Silent Titan Affecting Glycated Hemoglobin Reliability

Hemoglobin A1c (HbA1c) is a popular invaluable tool in the diagnosis of Type 2 diabetes for red blood cells (RBCs) with a lifespan of 120 days; however, many factors, including hemoglobinopathies, affect its accuracy. Sickle cell trait, primarily a benign medical condition, is a point mutation in only one of two beta-globin genes on chromosome 11. We performed a traditional review to identify how the sickle cell trait (SCT) affects the interpretation of HbA1c and the further implications it may have on the diagnosis and management of Type 2 diabetes. A literature search was performed using PubMed®/MEDLINE® and Google Scholar with formulated keywords (sickle cell trait, HbAS, HbA1c, glycosylated hemoglobin, diabetes, RBC lifespan, race, and genetics), with the majority of results being mainly observational studies. The National Glycohemoglobin Standardization Program (NGSP) is responsible for standardizing HbA1c results and also highlights factors that can interfere with HbA1c, including hemoglobin variants. Studies that utilize only an NGSP-certified method with no clinically significant interference by HbS in patients with and without SCT showed contrasting results. Additional studies showed that persons of African ancestry, the group to which the majority of SCT patients belong, have a higher HbA1c than non-Hispanic whites (NHWs), just based on race, and a greater probability of having glucose-6-phosphate dehydrogenase (G6PD) deficiency, which lowers HbA1c. The most extensive study investigating the RBC lifespan in SCT patients showed a reduction in the cell lifespan compared to normal patients; however, other smaller studies were contradictory. Our study highlights the need for hemoglobinopathy detection before or during HbA1c measurement in populations with a high degree of African ancestry and the importance of patient notification. It also shows that SCT affects the accuracy of HbA1c, through its likely reduction of RBC lifespan and its increased association with African ancestry and G6PD deficiency. This review recommends that for SCT patients with potential Type 2 diabetes, HbA1c should be used in combination with another diagnostic tool such as fasting blood glucose, fructosamine, or glycated albumin to decrease the chances of a missed diagnosis.

Chromium

Chromium occurs primarily in the trivalent state (III), which is the most stable form, or in the hexavalent state (VI), which is a strong oxidizing agent. Elemental chromium (0) does not occur naturally on earth. Trivalent chromium (III) is an essential trace metal necessary for the formation of glucose tolerance factor and for the metabolism of insulin. Commercial applications of chromium compounds include tanning (III), corrosion inhibition, plating, glassware-cleaning solutions, wood preservatives (VI), manufacture of safety matches, metal finishing (VI), and the production of pigments (III, VI). Hexavalent chromium (VI) contaminated local soil when chromium waste slag was part of the fill material present in residential, public, and industrial areas. In some urban areas, about two-thirds of the chromium in air results from the emission of hexavalent chromium from fossil fuel combustion and steel production. The remaining chromium in air is the trivalent form. The residence time of chromium in air is < 10 days, depending on the particle size. Trivalent compounds generally have low toxicity and the gastrointestinal tract poorly absorbs these compounds. Hexavalent chromium is a skin and mucous membrane irritant and some of these hexavalent compounds are strong corrosive agents. Hexavalent chromium compounds also produce an allergic contact dermatitis characterized by eczema. Sensitivity to trivalent compounds is much less frequent, but some workers may react to high concentrations of these compounds. Hexavalent chromium is recognized by the International Agency for Research on Cancer and by the US Toxicology Program as a pulmonary carcinogen. The increased risk of lung cancer occurs primarily in workers exposed to hexavalent chromium dust during the refining of chromite ore and the production of chromate pigments. Although individual studies suggest the possibility of an excess incidence of cancer at sites outside the lung, the results from these studies are inconsistent.

Radionuclide-labeled red blood cells: current status and future prospects

Radiolabeling of red cells and their clinical and research application in nuclear medicine constitute an area of continued interest and steady growth during the past two decades. Significant advances have been made so that at the present time, radiolabels with sufficient in vitro and in vivo stability are available for diverse applications. Technetium-99m-labeled red cells in particular have revolutionized the field of cardiovascular nuclear medicine by making possible the external evaluation of various heart parameters with minimum radiation dose or trauma to the patient. Among other areas of study that use 99mTc -RBC are blood pool imaging, detection of vascular malformations, red cell mass determination, detection of gastrointestinal bleeding, and of hemangiomas. Heat-damaged 99mTc -RBC find application in spleen imaging, accessory spleen localization, detection of GI bleeding, and in other areas. A critical evaluation is presented of the various in vitro and in vivo labeling techniques that are currently available for red cell labeling. Even though the presently used procedures provide satisfactory labeled preparations, ideal radioisotopic RBC labels remain to be developed. Intermediate (2-3 days) as well as long-lived (approximately 30 days) radionuclidic labels are highly desirable for a number of clinical procedures where 99mTc is not useful due to its short half-life. A clearer understanding of the mechanistic aspects of various labeling reactions is expected to aid in the design of better and improved RBC labels that will help fulfill various areas of need in nuclear medicine applications. New approaches such as the use of radiolabeled antibodies to red cell antigens, or labeling specific receptor sites in the cell may lead to substantial improvements in the labeling methodology and could yield labeled cells with the least damage and maximum in vivo stability.

Studies on the in vivo elution of 51Cr from baboon red blood cells

Four anticoagulant solutions were added to baboon red blood cells prior to labeling with 51Cr to determine how each would influence the distribution of 51Cr within the red blood cells, the loss of 51Cr from the red blood cells after transfusion, and the calculated red cell survival value. The 51Cr label was detected in the hemoglobin and in the low molecular weight compounds within the red blood cells. The elution of 51Cr from labeled baboon red blood cells following transfusion could not be explained by the distribution of 51Cr between hemoglobin and low molecular weight compounds within the red blood cells.

Influence of fluoride on the uptake of 51Cr-chromate by human erythrocytes

Uptake of 51Cr-chromate by freshly collected human erythrocytes was inhibited by 90 mM sodium fluoride only in cells preincubated with fluoride. In vitro storage also increased the sensitivity of the cells: 90 mM NaF clearly inhibited the uptake of chromate in cells stored in vitro for 5 weeks. Gel chromatography revealed two forms of 51Cr within the cells, one of small molecular weight, which thin layer chromatography indicated was unchanged chromate; the other form was apparently bound to macromolecules such as hemoglobin.

Binding of(51)Cr to human erythrocytes

Radioactive chromium accumulated in human erythrocytes exists in two forms: one bound to macromolecules, e.g., hemoglobin, and one in a low molecular weight form. Both forms are released from cells either spontaneously or as a result of toxic induction.

51Cr release cytotoxicity assay evaluated with fluoride and cadmium

The sensitivity of the 51Cr release assay was evaluated with two known cytotoxic agents; fluoride and cadmium. The sensitivity was far less than that of other assays, e.g. growth inhibition of cultured cells, and additional a two-peaked dose-response curve was found with cadmium.

Blood volume and extracellular space (ECS) of the whole body and some organs of the rat

Methods are described for estimation of blood volume and extracellular space (ECS) in the whole body and in some organs with 51Cr, 14C-thiocyanate and 3H-inulin. A mean blood volume of 47 ml/kg, a thiocyanate space of 350 ml/kg and a inulin space of 288 ml/kg were determined in the rat. The corresponding values of organs are shown in figures 1--3.

The spleen as a hematological organ

The spleen has multiple roles in human physiology. Eitht major functions are discussed in this review (hematopoiesis, erythrocyte destruction, hormonal function in hematopoiesis, culling and pitting, platelet and leukocyte destruction, particulate removal, reservoir function, and immunologic function). Splenic trapping of red cells, and the concepts of hypersplenism, are major responsibilities of this organ. These aspects are placed in perspective for the reader.