Laboratory Medicine: Anemia & Microcytic Anemia - PDF

Laboratory Medicine & Anemias Part 1: Intro & Microcytic Anemia Noah Chernik OMS-3 Academic Medicine Scholar [email protected] Dr. Greg Saggio, DO Associate Professor Department of Surgery [email protected] I am available to address any questions/comments/concerns and provide additional resources...

Laboratory Medicine & Anemias Part 1: Intro & Microcytic Anemia Noah Chernik OMS-3 Academic Medicine Scholar [email protected] Dr. Greg Saggio, DO Associate Professor Department of Surgery [email protected] I am available to address any questions/comments/concerns and provide additional resources or discussion. [email protected] Learning Objectives 1. Identify the most common causes of microcytic, normocytic, and macrocytic anemia. 2. Describe the pathophysiology, clinical symptomatology, and laboratory findings of the various causes of microcytic, normocytic, and macrocytic anemia. 3. Illustrate the biochemical basis of heme synthesis, vitamin B12 and folate deficiency, and the clinical approach to such patients. Lecture Layout General Concepts of Anemia Microcytic Anemia Normocytic Anemia Macrocytic Anemia Anemia Basics Anemia Basics Anemia: a significant deficit in the mass of circulating red blood cells Why do we care? - RBCs = transport oxygen to cells and tissues - Decreased RBCs → decreased capacity to carry and deliver oxygen Erythrocytes (Red Blood Cells) - Function: deliver O2 from the lungs to peripheral tissues and CO2 from the peripheral tissues to the lungs - Biconcave shape, anucleate cells and lack organelles. This is to increase the amount of cytoplasm in the cell - They are flexible, important when navigating small capillaries. This is due to special membrane proteins (more to follow) - Life Span: ~ 120 Days In healthy individuals, about ~1% of all RBCs are removed each day due to senescence (they’re old!) Erythrocyte Life Cycle - RBCs are produced in the bone marrow (erythropoiesis) - Erythropoietin (EPO) growth factor helps stimulate production Decreased O2 is sensed by interstitial cells in the peritubular capillary bed of the renal cortex → EPO secreted EPO & hematocrit levels are inversely proportional - Reticulocytes (immature RBCs) are released into circulation In ~24-48 hours they mature to erythrocytes Reticulocyte count is 1-2% of total RBCs Reticulocytes appear more basophilic (purple) compared to mature RBCs due to rRNA still present Proerythroblast Basophilic erythroblast Polychromatophilic erythroblast - Senescent (old) RBCs are removed by macrophages in the spleen, liver, and bone marrow - Reticuloendothelial System (RES) recycles the RBCs Orthochromatophilic Reticulocyte Erythrocyte erythroblast Anemia General Ideas - Anemia is generally viewed as Production vs Destruction of RBCs 1. Blood Loss Losing mature RBCs, but the ability to produce and destroy RBCs has not changed 2. Decreased RBC Production Can’t produce enough RBCs to keep up with destruction We usually see a decreased reticulocyte count 3. Increased RBC Destruction (Hemolysis) Destroying more RBCs than creating Usually, will see splenomegaly and jaundice due to increased RBC breakdown Clinical Presentation of Anemia - Signs and symptoms will vary with underlying etiologies - Body is responding to the resulting tissue hypoxia due to decreased O2 - Weakness, malaise, fatigue, dyspnea on mild exertion - Pallor (conjunctiva & skin are pale) - Spoon nails, dizziness - Headache, lightheadedness, faintness, dimness of vision - Angina pectoris/Cardiac failure - Specific underlying pathology may have unique signs/symptoms - ie: sickle cell disease & pain/renal failure SOURCE: https://www.phlbi.org/divisions/blood-disorders/anemia/ - Symptoms are broad, do not correlate with hemoglobin levels per say Measurements of Anemia CBC Rule of 3: RBC Count (5) Hemoglobin (15) Hematocrit (45) SOURCE: https://www.healthtestingcenters.com/cbc-blood-test-explained/ Clinical Pearl: - 1 Unit of packed RBC - Hemoglobin increase by 1 g/dL - Hematocrit increase by 3% Measurements of RBCs 1. Red Blood Cell Count: number of RBCs in the blood Males: 4.3-5.9 × 1012 per L Females: 3.5-5.5 × 1012 per L 2. Hemoglobin (Hgb): concentration of Hgb in the blood Reflects an erythrocyte’s ability to carry oxygen Males: 14-18 g/dL Females: 12-16 g/dL 3. Hematocrit (Hct): measures the percentage of erythrocyte volume in the blood sample Males: 40-54% Females: 36-48% Patients with anemia typically have low Hgb and Hct. Usually also see low RBC count https://exchange.scholarrx.com/brick/blood-foundations-and-frameworks Hemoglobin Hemoglobin is the oxygen carrying aspect of the RBC It is composed of Heme (Iron + Protoporphyrin) Globin (Four total chains) Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 9e RBC Indices Size of RBCs: 1. Mean Cell Volume (MCV): average size of RBCs Both Genders: 80-100 fL 2. Red Blood Cell Distribution Width (RDW): measures the variability of the MCV Both Genders: 12-15% Shows if the erythrocytes are all the same or if they are different in sizes or shapes Higher RDW means large range of size Amount of hemoglobin per RBC: 1. Mean Corpuscular Hemoglobin (MCH): amount of Hgb in an average erythrocyte 2. Mean Corpuscular Hemoglobin Concentration (MCHC): provides the percentage of Hgb concentration in an average erythrocyte Other: 1. Reticulocyte Count: the percentage of total RBCs that are reticulocytes (immature RBCs) This is important when determining if the bone marrow is responding appropriately to anemia Anemia with ↑ reticulocyte count, bone marrow is responding appropriately Anemia without ↑ reticulocyte count, bone marrow may be the issue for the anemia Remember, bone marrow takes time to respond, so there will be a DELAY Peripheral Blood Smear Follow up test for abnormal CBC Visually inspect RBC shape and color A Wright Giemsa stain is used When examining a normal peripheral blood smear, notice the central area of pallor on the RBCs This is due to the biconcave-disk shape, meaning the central region of the cell contains very little cytoplasm Less cytoplasm means less hemoglobin. Hemoglobin is responsible for the coloring of the RBC https://exchange.scholarrx.com/brick/red-blood-cell-laboratory-tests Anemia Classification When working someone up for potential anemia, the first test you will order is a CBC If the hemoglobin/hematocrit/RBC is LOW, your patient is anemic by definition To determine the type of anemia your patient may have, the next best lab value to examine is the mean cell volume (MCV) The MCV measures the average size of the RBCs Microcytic = MCV 100  Sideroblastic First Aid for the USMLE Step 1 2024, Page 422 Microcytic Anemias (MCV < 80) Microcytic Anemias 1. Iron Deficiency Anemia (Later Stages) 2. Anemia of Chronic Disease (Later Stages) 3. Lead Poisoning 4. Sideroblastic Anemia 5. Thalassemia Your red blood cells are smaller than normal! For anemia of chronic disease and iron deficiency anemia, you will typically see a higher RDW, as these two anemias start as normocytic Normocytic anemia has larger RBCs, as the disease progresses the RBCs become smaller Therefore, we have a greater mix (higher variance) of RBC size in the blood, increasing the RDW RBC Division - Erythroblasts: RBC progenitor cells in the bone marrow Normal Hgb Low Hgb - As the RBC divides and matures, they become smaller - This is due to RBCs maintaining a specific concentration of hemoglobin in the cell to function Hgb properly - Microcytic Anemia: Cell Cell - Due to the decreased production of hemoglobin Division Division - Since there is less hemoglobin, the RBC must undergo addition cell division to maintain the concentration of hemoglobin in the cell Normocytic Cell Division Microcytic Due to lower hemoglobin concentration, additional cell division necessary Microcytic Anemia There is an issue with creating hemoglobin Hemoglobin is responsible for the pigmentation of the RBC Less hemoglobin → hypopigmentation (hypochromatic RBC) RBCs under the microscope will appear paler due to the lack of pigment Additionally due to the decreased hemoglobin, the central area of pallor will appear larger in microcytic anemia Labs for Microcytic Anemia Once a diagnosis of microcytic anemia is made, the next best step is to order an iron study Results of an Iron Study: Serum Iron: measures the amount of iron in the blood Serum Ferritin: this reflects the amount of iron stored in the bone marrow macrophages and liver Remember, ferritin is the protein that stores iron Total Iron Binding Capacity: the amount of transferrin circulating in the blood TIBC is transferrin Transferrin is made in the liver. There is a relationship between iron storage (ferritin) and TIBC. When iron stores in the bone marrow are low, signals are sent to the liver to produce MORE transferrin. Therefore, transferrin is increased (hence why TIBC is high in iron deficiency anemia) % Saturation: the percentage of transferrin that is bound to iron (~33% is normal) This is a calculation (serum iron⁄TIBC) Ferritin and TIBC are generally opposite If we have increased ferritin (increased iron storage), our binding capacity (TIBC) is low Liver will produce less transferrin because cells are full of iron) If we have decreased ferritin (decreased iron storage), our binding capacity (TIBC) is high Liver gets signals to make more transferrin because cells need more iron Microcytic Anemias: Iron Deficiency Anemia  Iron Deficiency Anemia Without iron, the body cannot produce heme Most common cause of anemia worldwide (>12% of world’s population*) Iron loss > Iron intake Iron excretion is not regulated Bleeding (GI bleeding/cancer; menses in females) Loss of epithelial cells from skin, gut, genitourinary tract Can be due to iron intake issues Iron is absorbed in the duodenum Any issue with the duodenum can affect uptake (disease, surgery) Inadequate nutritional iron intake General Treatment: oral iron supplement *UptoDate: Causes and diagnosis of iron deficiency and iron deficiency anemia in adults  Iron: Iron absorbed in duodenum Iron Metabolism Fist: Folate (B9) absorbed in small bowel Bro: B12 absorbed in terminal ileum Iron in the body is recycled between circulated and stored pools. Iron is carried by transferrin in the plasma. Transferrin is a protein synthesized in the liver Main function of transferrin: deliver iron to cells to help synthesize hemoglobin Iron Transport from the GI System 1. Iron is consumed in heme (meat) and non-heme (vegetable) 2. Iron is absorbed by enterocytes in the duodenum 3. Non-heme iron (Fe3+) must be reduced from Fe3+ to Fe2+ by ferrireductase (cytochrome B) on the surface of the enterocyte. It is then transported into the cell by DMT1 4. Heme is absorbed by transporters into the enterocyte 5. All iron leaves the enterocyte via ferroportin 6. Once in the plasma, iron is transported via transferrin 7. Transferrin will take iron to its final destination (macrophages in the marrow and liver), iron will be stored by ferritin Hepcidin: regulates this process by decreasing ferroportin Robbins & Cotran Pathologic Basis of Disease, 10e Iron Metabolism Takeaways Iron is absorbed in the duodenum Heme iron (animal iron) is absorbed better. Non-heme iron (plant) must be converted to Fe2+ and is absorbed via DMT1 Once iron is absorbed into the duodenal enterocytes, it must leave the cell via ferroportin In the plasma, iron is attached to transferrin to be transported In the cell, iron is attached to ferritin to be stored Hepcidin is an acute phase reactant that regulates this process by decreasing ferroportin Decreasing ferroportin will decrease the amount of iron allowed into the body from the GI system Robbins & Cotran Pathologic Basis of Disease, 4e Usual Causes of Iron Deficiency Major Causes: Blood loss Dietary deficiency (most iron comes from meat and vegetables) Most Common Causes by Age Infants: breast feeding (human milk) is naturally low in iron Children: poor diet Adults (20-50): Males: peptic ulcer disease Females: menorrhagia (increase blood loss w/ menses) or pregnancy (increase overall iron demands) Elderly: Western world: colon polyps/cancer Developing world: hookworms *Clinical Pearl: any elderly individual with iron deficiency anemia is deemed to have colon cancer until proven otherwise Other Causes to Keep in Mind: Malnutrition Malabsorption → celiac disease Surgery → gastric bypass surgery (food bypasses duodenum) and gastrectomy (stomach acid helps increase Fe2+ Stages of Iron Deficiency 1. Storage of iron is depleted in the cells Ferritin  TIBC  Cells will recruit more iron from the plasma 2. Serum iron is depleted Serum iron  % Saturation  TIBC  3. Normocytic Anemia (Early Stage): the body will begin to make normal sized RBCs, but will reduce the quantity. MCV: 80-100 Hemoglobin/Hematocrit/RBC:  RDW: normal 4. Microcytic/Hypochromic Anemia (Later Stage): bone marrow will make smaller RBCs to conserve the concentration on hemoglobin, and fewer cells are made Scandinavian Journal of Clinical and Laboratory Investigation, Volume 74 (2014) MCV: