{"id":1105,"date":"2021-08-25T12:58:00","date_gmt":"2021-08-25T12:58:00","guid":{"rendered":"https:\/\/www.osmosis.org\/blog\/?p=1105"},"modified":"2025-10-01T11:42:37","modified_gmt":"2025-10-01T19:42:37","slug":"usmle-step-1-question-of-the-day-macrocytic-anemia","status":"publish","type":"post","link":"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia","title":{"rendered":"USMLE\u00ae Step 1 Question of the Day: Macrocytic Anemia"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_80 ez-toc-wrap-center counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">In This Article<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\/#The_correct_answer_to_todays_USMLE%C2%AE_Step_1_Question_is%E2%80%A6\" >The correct answer to today&#8217;s USMLE\u00ae Step 1 Question is&#8230;<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\/#Incorrect_answer_explanations\" >Incorrect answer explanations<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\/#Main_Explanation\" >Main Explanation<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\/#Major_Takeaway\" >Major Takeaway<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\/#References\" >References<\/a><\/li><\/ul><\/nav><\/div>\n\n<p class=\"wp-block-paragraph\"><strong><em>Each week, Osmosis shares a USMLE\u00ae Step 1-style practice question to test your knowledge of medical topics. Today&#8217;s case involves a 25-year-old woman with symptoms of fatigue and reduced exercise tolerance.&nbsp;<\/em><\/strong><strong><em>Can you figure out the cause?<\/em><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A 25-year-old woman presents to her outpatient provider for symptoms of fatigue and reduced exercise tolerance that started 2 weeks ago. Past medical history is notable for a seizure disorder that is currently managed with&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Nonbenzodiazepine_anticonvulsants\" target=\"_blank\" rel=\"noreferrer noopener\">phenytoin<\/a>. In addition, the patient had an episode of&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Acute_pyelonephritis\" target=\"_blank\" rel=\"noreferrer noopener\">pyelonephritis<\/a>&nbsp;several weeks ago that was successfully treated with trimethoprim-sulfamethoxazole. The patient has&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Menstrual_cycle\" target=\"_blank\" rel=\"noreferrer noopener\">menstrual periods<\/a>&nbsp;every 28 days, and denies dysmenorrhea and menorrhagia. Physical examination is notable for conjunctival pallor. Laboratory testing reveals a hemoglobin on 9.3 g\/dL. A peripheral blood smear is performed and shows the following:<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"474\" height=\"474\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/red-blood-cells.png\" alt=\"Red blood cells with purple round parts in one of the cells.\" class=\"wp-image-1106\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/red-blood-cells.png 474w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/red-blood-cells.png?resize=150,150 150w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/red-blood-cells.png?resize=300,300 300w\" sizes=\"auto, (max-width: 474px) 100vw, 474px\" \/><\/figure>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\">Reproduced from:&nbsp;<a href=\"https:\/\/www.flickr.com\/photos\/euthman\/8612790151\" target=\"_blank\" rel=\"noreferrer noopener\">Flickr<\/a>&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Which of the following sets of red blood cell characteristics is most likely to be seen in this patient?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A.<\/strong>&nbsp;Impaired Process:<strong>&nbsp;Heme Synthesis,&nbsp;<\/strong>Red Blood Cell Maturity:<strong>&nbsp;Immature,&nbsp;<\/strong>Mean Corpuscular Volume:<strong>&nbsp;75 mm<sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>B.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>DNA Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Mature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>75 mm<sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>Heme Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Mature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>105 mm<sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>D.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>DNA Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Immature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>105 mm<sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>DNA Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Mature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>105 mm<sup>3<\/sup><\/strong><br>Scroll down to find the answer!<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-rich is-provider-embed-handler wp-block-embed-embed-handler wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"Everybody loves Osmosis.org\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/kizbJZ9cdLg?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><strong><em><a href=\"https:\/\/www.osmosis.org\/plans\" target=\"_blank\" rel=\"noreferrer noopener\"><u><em><strong>\u2192 Reinforce your understanding with more self-assessment items on Osmosis.<\/strong>\u00a0<\/em><\/u><\/a><\/em><\/strong><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"The_correct_answer_to_todays_USMLE%C2%AE_Step_1_Question_is%E2%80%A6\"><\/span>The correct answer to today&#8217;s USMLE\u00ae Step 1 Question is&#8230;<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>D.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>DNA Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Immature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>105 mm<\/strong><strong><sup>3<\/sup><\/strong>Before we get to the&nbsp;<strong>Main Explanation<\/strong>, let&#8217;s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Incorrect_answer_explanations\"><\/span>Incorrect answer explanations<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The incorrect answers to today&#8217;s USMLE\u00ae Step 1 Question are&#8230;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A.<\/strong>&nbsp;Impaired Process:<strong>&nbsp;Heme Synthesis,&nbsp;<\/strong>Red Blood Cell Maturity:<strong>&nbsp;Immature,&nbsp;<\/strong>Mean Corpuscular Volume:<strong>&nbsp;75 mm<\/strong><strong><sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:<\/strong>&nbsp;Iron deficiency,&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Lead_poisoning\" target=\"_blank\" rel=\"noreferrer noopener\">lead poisoning<\/a>, and&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Beta-thalassemia\" target=\"_blank\" rel=\"noreferrer noopener\">thalassemias<\/a>&nbsp;can impair heme synthesis and result in a microcytic anemia. Female patients are generally at higher risk of iron deficiency due to menstrual blood loss. However, this patient has no history of overly frequent or heavy&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Menstrual_cycle\" target=\"_blank\" rel=\"noreferrer noopener\">menses<\/a>. In contrast, the patient\u2019s history of phenytoin and trimethoprim-sulfamethoxazole use puts her at risk of&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Folate_(Vitamin_B9)_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">folate deficiency<\/a>, which is a more likely cause of her anemia.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>B.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>DNA Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Mature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>75 mm<\/strong><strong><sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>In normal red blood cell (RBC) development, large red blood cell precursors (erythroblasts) undergo DNA replication and cellular division. This results in the creation of several smaller mature RBCs. Impaired&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/DNA_replication\" target=\"_blank\" rel=\"noreferrer noopener\">DNA replication<\/a>&nbsp;would prevent RBC maturation and cause immature and macrocytic (mean corpuscular volume &gt; 100 mm<sup>3<\/sup>) RBCs to be observed on laboratory testing.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>Heme Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Mature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>105 mm<\/strong><strong><sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Iron deficiency, lead poisoning, or thalassemia can result in impaired heme synthesis. DNA synthesis will be unaffected and hence the RBCs will be mature. However, the RBCs will most likely be microcytic. This is because the body attempts to preserve a normal RBC hemoglobin concentration. So when hemoglobin production is decreased, the body makes smaller RBCs to compensate. &nbsp;&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E.<\/strong>&nbsp;Impaired Process:&nbsp;<strong>DNA Synthesis,<\/strong>&nbsp;Red Blood Cell Maturity:&nbsp;<strong>Mature,<\/strong>&nbsp;Mean Corpuscular Volume:&nbsp;<strong>105 mm<\/strong><strong><sup>3<\/sup><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:<\/strong>&nbsp;Causes of impaired&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/DNA_replication\" target=\"_blank\" rel=\"noreferrer noopener\">DNA replication<\/a>&nbsp;include&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Vitamin_B12_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">vitamin B12 deficiency<\/a>, folate deficiency, orotic aciduria, and Fanconi anemia. However, defects in DNA synthesis would hinder RBC maturation and cause immature RBCs to be found in the patient\u2019s circulation.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Main_Explanation\"><\/span><strong>Main Explanation<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This patient is taking phenytoin and trimethoprim-sulfamethoxazole. Phenytoin impairs folate absorption. Trimethoprim-sulfamethoxazole prevents the conversion of folate into tetrahydrofolate, the active form used in DNA synthesis. As a result, this patient most likely has&nbsp;<strong>impaired DNA synthesis secondary to&nbsp;<\/strong><strong><a href=\"https:\/\/www.osmosis.org\/learn\/Folate_(Vitamin_B9)_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">folate deficiency<\/a><\/strong>, which results in&nbsp;<strong><a href=\"https:\/\/www.osmosis.org\/learn\/Macrocytic_anemia:_Pathology_review\" target=\"_blank\" rel=\"noreferrer noopener\">macrocytic megaloblastic anemia<\/a><\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Macrocytic anemias (MCV &gt; 100 mm<sup>3<\/sup>) can be&nbsp;<strong>classified based on the presence\/absence of&nbsp;<\/strong><strong><a href=\"https:\/\/www.osmosis.org\/learn\/Megaloblastic_anemia\" target=\"_blank\" rel=\"noreferrer noopener\">megaloblasts<\/a><\/strong>. Megaloblasts are&nbsp;<strong>large, immature red blood cells&nbsp;<\/strong>produced when the cytoplasm develops normally, but the&nbsp;<strong>DNA synthesis is impaired<\/strong>&nbsp;and cell division is delayed. Therefore, when there are defects in DNA synthesis or repair (e.g.,&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Folate_(Vitamin_B9)_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">folate deficiency<\/a>,&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Vitamin_B12_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">vitamin B12 deficiency<\/a>, Fanconi anemia, orotic aciduria, etc.) there will be megaloblastic macrocytic anemia. Megaloblastic anemia can also affect white blood cell production, resulting in the release of immature neutrophils with hypersegmented nuclei into the bloodstream. The observation of these&nbsp;<strong>hypersegmented neutrophils<\/strong>&nbsp;on peripheral blood smear can help distinguish megaloblastic from non-megaloblastic anemias.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In contrast,&nbsp;<strong>non-megaloblastic&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Macrocytic_anemia:_Pathology_review\" target=\"_blank\" rel=\"noreferrer noopener\">macrocytic anemias<\/a>&nbsp;<\/strong>arise from&nbsp;<strong>conditions that do not affect DNA synthesis<\/strong>. Causes of non-megaloblastic macrocytic anemia include Diamond-Blackfan Anemia, which results from a defect in protein synthesis, and chronic alcohol use, which has a toxic effect on the bone marrow. <\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"Macrocytic anemias ~high yield~\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/n8Ni2mvJTUE?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Major_Takeaway\"><\/span><strong>Major Takeaway<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong><a href=\"https:\/\/www.osmosis.org\/learn\/Macrocytic_anemia:_Pathology_review\" target=\"_blank\" rel=\"noreferrer noopener\">Macrocytic anemias<\/a><\/strong>&nbsp;are characterized by the presence of RBCs with a&nbsp;<strong>mean corpuscular volume exceeding 100 mm<\/strong><strong><sup>3<\/sup><\/strong>. They can be divided into&nbsp;<strong><a href=\"https:\/\/www.osmosis.org\/learn\/Megaloblastic_anemia\" target=\"_blank\" rel=\"noreferrer noopener\">megaloblastic anemia<\/a><\/strong>, where DNA synthesis is impaired, and&nbsp;<strong>non-megaloblastic anemia<\/strong>. Causes of megaloblastic macrocytic anemia include&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Folate_(Vitamin_B9)_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">folate deficiency<\/a>,&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Vitamin_B12_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">vitamin B12 deficiency<\/a>, orotic aciduria, and&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Fanconi_anemia\" target=\"_blank\" rel=\"noreferrer noopener\">Fanconi anemia<\/a>. Causes of non-megaloblastic macrocytic anemia include&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Diamond-Blackfan_anemia\" target=\"_blank\" rel=\"noreferrer noopener\">Diamond-Blackfan<\/a>&nbsp;anemia and chronic alcohol use.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"References\"><\/span><strong>References<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Agabegi, S.S., Agabegi, E.D. (2012)&nbsp;<em>Step-Up to Medicine<\/em>. Wolters Kluwer\/Lippincott Williams &amp; Wilkins. ISBN: 978-1609133603.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Aslinia, F., Mazza, J.J. (2006) Megaloblastic anemia and other causes of macrocytosis.&nbsp;<em>Clinical Medicine &amp; Research<\/em>. 4(3), 236-241. Doi:&nbsp;<a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/16988104\/\" target=\"_blank\" rel=\"noreferrer noopener\">10.3121\/cmr.4.3.236.<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Moore, C.A., Adil, A. (2019) Macrocytic anemia.&nbsp;<em>StatPearls [Internet]<\/em>. Web Address:&nbsp;<a href=\"https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK459295\/?report=classic\" target=\"_blank\" rel=\"noreferrer noopener\">https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK459295\/?report=classic<\/a>.<\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><em><strong>_________________________<\/strong><br><br><strong>Want more USMLE\u00ae Step 1 practice questions? Try Osmosis today! Access your&nbsp;<em><strong><a href=\"https:\/\/www.osmosis.org\/login?type=create\" target=\"_blank\" rel=\"noreferrer noopener\">free trial<\/a><\/strong><\/em>&nbsp;and find out why millions of current and future clinicians and caregivers love learning with us.<\/strong><\/em><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><a href=\"https:\/\/www.osmosis.org\/plans\" target=\"_blank\" rel=\"noreferrer noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"250\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-02T195148.146.png?w=700\" alt=\"Osmosis ad\" class=\"wp-image-701\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-02T195148.146.png 700w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-02T195148.146.png?resize=300,107 300w\" sizes=\"auto, (max-width: 700px) 100vw, 700px\" \/><\/a><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><em><em><sub>The United States Medical Licensing Examination (USMLE\u00ae) is a joint program of the Federation of State Medical Boards (FSMB\u00ae) and National Board of Medical Examiners (NBME\u00ae). Osmosis is not affiliated with NBME nor FSMB.&nbsp;<\/sub><\/em><\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Each week, Osmosis shares a USMLE\u00ae Step 1-style practice question to test your knowledge of medical topics. Today&#8217;s case involves a 25-year-old woman with symptoms of fatigue and reduced exercise tolerance.&nbsp;Can you figure out the cause? A 25-year-old woman presents to her outpatient provider for symptoms of fatigue and reduced exercise tolerance that started 2 [&hellip;]<\/p>\n","protected":false},"author":202,"featured_media":1107,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[27,20,1369,44],"tags":[],"class_list":["post-1105","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-medicine","category-exam-prep","category-step-1-questions","category-step-1"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v23.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>USMLE\u00ae Step 1 Question of the Day: Macrocytic Anemia - Osmosis Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"USMLE\u00ae Step 1 Question of the Day: Macrocytic Anemia - Osmosis Blog\" \/>\n<meta property=\"og:description\" content=\"Each week, Osmosis shares a USMLE\u00ae Step 1-style practice question to test your knowledge of medical topics. Today&#8217;s case involves a 25-year-old woman with symptoms of fatigue and reduced exercise tolerance.&nbsp;Can you figure out the cause? A 25-year-old woman presents to her outpatient provider for symptoms of fatigue and reduced exercise tolerance that started 2 [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\" \/>\n<meta property=\"og:site_name\" content=\"Osmosis Blog\" \/>\n<meta property=\"article:published_time\" content=\"2021-08-25T12:58:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-10-01T19:42:37+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/usmle-macrocytic-anemia.webp\" \/>\n\t<meta property=\"og:image:width\" content=\"1081\" \/>\n\t<meta property=\"og:image:height\" content=\"1081\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/webp\" \/>\n<meta name=\"author\" content=\"Marina Horiates Kerekes, MD &amp; Team\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":[\"Article\",\"BlogPosting\"],\"@id\":\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-macrocytic-anemia\"},\"author\":{\"name\":\"Marina Horiates Kerekes, MD &amp; 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Her past medical history is significant for\u00a0hypertension\u00a0and\u00a0hyperlipidemia, but notes no recent travel, sick contacts, or illnesses. 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