Looking at Labs

Hemoglobin level

Background Clinical alert • Increased Hb levels are found in: Hemoglobin (Hb), the main An Hb value less than 5.0 g/dL ° vera component of erythrocytes (red (50 g/L) can lead to heart failure ° heart failure blood cells [RBCs]), serves as the and death. A value greater than ° chronic obstructive pulmonary vehicle for the transportation 20 g/dL (200 g/L) can lead to disease of oxygen and carbon dioxide. obstruction of the capillaries as a • Variation in Hb levels: It is composed of amino acids result of hemoconcentration. ° occurs after transfusions, that form a single protein called hemorrhages, burns. (Hb and globin, and a compound called Clinical implications HCT are both high during heme, which contains iron atoms • Decreased Hb levels are found and immediately after hemor- and the red pigment porphyrin. in states (a condition in rhage.) It is the iron pigment that com- which there is a reduction of Hb, ° The Hb and HCT provide bines readily with oxygen and hematocrit [HCT], or RBC val- valuable information in an gives blood its characteristic red ues). The Hb must be evaluated emergency if they are inter- color. Each gram of Hb can carry along with the RBC count and preted not in an isolated fash- 1.34 mL of oxygen per 100 mL HCT. ion but in conjunction with of blood. The oxygen-combining ° iron deficiency, , other pertinent lab data. capacity of the blood is directly pernicious anemia, hemoglo- ° Hb variants can cause varia- proportional to the Hb concentra- binopathies tion in measured Hb: tion rather than to the RBC count ° disease, hypothyroidism  methemoglobin because some RBCs contain more ° hemorrhage (chronic or acute)  sickle cell hemoglobin Hb than others. Therefore, Hb ° caused by:  fetal hemoglobin determinations are important in  transfusions of incompatible  deoxyhemoglobin. the evaluation of anemia. blood The Hb determination is part  reactions to chemicals or Clinical implications of of a complete blood cell count. drugs polycythemia It is used to screen for disease  reactions to infectious agents Polycythemia is the term used to associated with anemia, to deter-  reactions to physical agents describe an abnormal increase in mine the severity of anemia, to (severe burns, artificial heat the number of RBCs. Although monitor the response to treat- valves) there are several tests to directly ment for anemia, and to evaluate ° various systemic diseases, determine the RBC mass, these polycythemia. Hb also serves as including: tests are expensive and some- an important buffer in the extra-  Hodgkin disease what cumbersome. For screen- cellular fluid.  ing purposes, we rely on the  HCT and Hb to evaluate polycy- Normal findings  systemic lupus erythemato- themia indirectly. • Women: 12.0 to 16.0 g/dL or sus are classified as follows: 120 to 160 g/L  carcinomatosis • Relative polycythemia: an • Men: 14.0 to 17.4 g/dL or 140 to  sarcoidosis increase in Hb, HCT, or RBC 174 g/L.  renal cortical necrosis count caused by a decrease in

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Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved. the plasma volume (dehydration, Clinical implications of ° hemorrhagic: acute blood spurious erythrocytosis from anemia loss stress or smoking) are classified as follows: ° hemolytic: a premature, accel- • Absolute or true polycythemia. • hypoproliferative anemias (inad- erated destruction of RBCs ° primary () equate production of RBCs)  immune hemolysis ° secondary ° marrow aplasia   appropriate (an appropriate ° myelophthisic anemia  toxic hemolysis (physical– response to ° anemia with blood dyscrasias chemical) physiologic conditions) ° anemia of chronic disease  traumatic or microangiopath- – high altitude ° anemia with organ failure ic hemolysis – cardiopulmonary disorder • maturation defect anemias  hypersplenism – increased affinity for oxygen ° cytoplasmic: hypochromic  enzymopathies  inappropriate (an overpro- anemias  parasitic infections duction of RBCs not neces- ° nuclear: megaloblastic anemias ° dilutional anemias sary to deliver oxygen to the ° combined: myelodysplastic  pregnancy tissues) syndromes  splenomegaly. ■ – renal tumor or cyst • hyperproliferative anemias – hepatoma (decreased Hb or HCT despite an – cerebellar hemangioblastoma increased production of RBCs) DOI-10.1097/01.CCN.0000660408.76985.53

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Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.