{"id":2062,"date":"2021-04-07T17:49:00","date_gmt":"2021-04-07T17:49:00","guid":{"rendered":"https:\/\/www.osmosis.org\/blog\/?p=2062"},"modified":"2025-10-01T11:42:38","modified_gmt":"2025-10-01T19:42:38","slug":"usmle-step-1-question-of-the-day-factor-v-leiden","status":"publish","type":"post","link":"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden","title":{"rendered":"USMLE\u00ae Step 1 Question of the Day: Factor V Leiden"},"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-factor-v-leiden\/#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><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#E_Factor_V_Leiden_deficiency\" >E. Factor V Leiden deficiency&nbsp;<\/a><\/li><\/ul><\/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-factor-v-leiden\/#Incorrect_answer_explanations\" >Incorrect answer explanations<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#A_Protein_S_deficiency\" >A. Protein S deficiency<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#B_Prothrombin_gene_mutation\" >B. Prothrombin gene mutation<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#C_Antiphospholipid_syndrome\" >C. Antiphospholipid syndrome<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#D_Antithrombin_deficiency\" >D. Antithrombin deficiency<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#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-9\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#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-10\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\/#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 breathing difficulties and chest pain. Labs show an elevated d-dimer. Purified protein C is added to the patient\u2019s plasma and causes no change in the lab values.&nbsp;<\/em><\/strong><strong><em><strong><em><strong><em>Can you figure it out?<\/em><\/strong><\/em><\/strong><\/em><\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A 25-year-old Caucasian woman presents to the emergency department due to difficulty breathing. Two hours ago, she suddenly felt chest pain accompanied by dyspnea. The patient denies any recent trauma, and she does not smoke or use illicit drugs. She is sexually active with her partner and uses condoms for contraception. The patient\u2019s temperature is 37.1\u00b0C (98.8\u00b0F), pulse is 75\/min, and blood pressure is 118\/73 mmHg. On physical examination, the patient appears distressed. Heart sounds are normal and the lungs are clear to auscultation. Labs show an elevated d-dimer. PT and PTT are 12 and 10 seconds, respectively. Purified protein C is added to the patient\u2019s plasma and causes no change in the lab values. Which of the following is the most likely diagnosis?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A. Protein S deficiency<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>B. Prothrombin gene mutation&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C. Antiphospholipid syndrome<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>D. Antithrombin deficiency<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E. Factor V Leiden deficiency&nbsp;<\/strong>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=\"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<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"E_Factor_V_Leiden_deficiency\"><\/span>E. Factor V Leiden deficiency&nbsp;<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">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<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"A_Protein_S_deficiency\"><\/span>A. Protein S deficiency<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Protein S is a&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Role_of_Vitamin_K_in_coagulation\" target=\"_blank\" rel=\"noreferrer noopener\">vitamin K<\/a>-dependent protein that serves as a cofactor for activated protein C to inactivate the procoagulant factors Va and VIIIa, thereby reducing thrombin generation. Protein S also functions as a cofactor for activated protein C in augmenting&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Clot_retraction_and_fibrinolysis\" target=\"_blank\" rel=\"noreferrer noopener\">fibrinolysis<\/a>. Deficiency of protein S may occur due to mutations and leads to hypercoagulability, resulting in&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Pulmonary_embolism\" target=\"_blank\" rel=\"noreferrer noopener\">pulmonary embolism<\/a>. Although&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Protein_S_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">protein S deficiency<\/a>&nbsp;is difficult to distinguish from factor V Leiden deficiency, the former is far rarer and therefore less likely.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"B_Prothrombin_gene_mutation\"><\/span>B. Prothrombin gene mutation<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Prothrombin, also known as factor II, is the precursor of thrombin, the end product of the coagulation cascade. Thrombin\u2019s main role is to proteolytically cleave fibrinogen to fibrin, which in turn crosslinks to form a fibrin clot. It also interacts with other hemostatic components. The G20210A point mutation in the prothrombin gene results in a gain-of-function of prothrombin that leads to hypercoagulability. However, the failure to change PTT after adding purified protein C favors another diagnosis.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"C_Antiphospholipid_syndrome\"><\/span>C. Antiphospholipid syndrome<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong><a href=\"https:\/\/www.osmosis.org\/learn\/Antiphospholipid_syndrome\" target=\"_blank\" rel=\"noreferrer noopener\">Antiphospholipid syndrome<\/a>&nbsp;(APS) refers to an autoimmune condition characterized by venous and\/or arterial thrombosis due to the presence of antiphospholipid antibodies (lupus anticoagulant, anticardiolipin, anti-\u03b22 glycoprotein I antibodies). It is most commonly associated with&nbsp;<a href=\"https:\/\/www.osmosis.org\/learn\/Systemic_lupus_erythematosus\" target=\"_blank\" rel=\"noreferrer noopener\">systemic lupus erythematosus<\/a>&nbsp;(SLE). Patients with APS often show prolonged PTT. In contrast, this patient shows no features of SLE and has reduced PTT.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"D_Antithrombin_deficiency\"><\/span>D. Antithrombin deficiency<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong><a href=\"https:\/\/www.osmosis.org\/learn\/Antithrombin_III_deficiency\" target=\"_blank\" rel=\"noreferrer noopener\">Antithrombin<\/a>&nbsp;(AT, previously called AT III) deficiency may be acquired or inherited in an autosomal dominant fashion with variable penetration. Antithrombin is a natural anticoagulant that inhibits thrombin (factor IIa), factor Xa, and other factors in the coagulation cascade. A variety of mutations have been recognized. AT has no direct effect on the PT, PTT, or thrombin time. Instead, it diminishes the increase in PTT following heparin administration. This phenomenon exists since heparin, an indirect inhibitor of thrombin and factor Xa, requires functional AT to be effective.<\/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 young patient who has no acquired risk factors for hypercoagulability (e.g., smoking, OCP use) is presenting with a pulmonary embolism, raising concerns for a hereditary cause.&nbsp;<strong><a href=\"https:\/\/www.osmosis.org\/learn\/Factor_V_Leiden\" target=\"_blank\" rel=\"noreferrer noopener\">Factor V Leiden<\/a><\/strong>&nbsp;is the&nbsp;<strong>most common inherited hypercoagulability disorder&nbsp;<\/strong>in Caucasians with venous thromboembolism (VTE). Patients may be homozygous or heterozygous.heterozygous.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"517\" height=\"288\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-11T115036.520.png\" alt=\"Venous thromboembolisms diagnosis: recurrent, family history, young age. Coagulation studies.\" class=\"wp-image-2064\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-11T115036.520.png 517w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-11T115036.520.png?resize=300,167 300w\" sizes=\"auto, (max-width: 517px) 100vw, 517px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Factor V is a procoagulant clotting factor that is synthesized as an inactive form and activated by thrombin at the wound site. Activated factor V then functions as a cofactor in the production of more thrombin from prothrombin. However, thrombin also halts its own production via a negative feedback loop. It does so by&nbsp;<strong>activating protein C<\/strong>&nbsp;(aPC), a protease that deactivates factor Va and factor VIIIa, thereby reducing thrombin production.production.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"454\" height=\"251\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-11T115118.151.png\" alt=\"Treatment: anticoagulant medication, no role for prophylaxis, exceptions: high risk surgery, pregnancy, additional thrombophilic mutations.\" class=\"wp-image-2065\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-11T115118.151.png 454w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/2024-09-11T115118.151.png?resize=300,166 300w\" sizes=\"auto, (max-width: 454px) 100vw, 454px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Factor V Leiden deficiency is caused by a single point mutation in the factor V gene in which guanine is switched to adenine. The corresponding mRNA codon forms a polypeptide chain in which arginine is replaced by glutamine at position Arg506. Consequently,&nbsp;<strong>the cleavage site&nbsp;<\/strong>is altered and factor V can no longer be degraded by protein C.<\/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=\"Factor V leiden - an Osmosis Preview\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/x6N4_BgCQks?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=\"wp-block-paragraph\">Patients are at increased risk for venous or arterial thromboembolism, MI, stroke, and obstetric complications. Laboratory testing often shows shortened or normal PTT. Diagnosis can be made via functional assay by demonstrating failure to prolong PTT with the addition of purified protein C (<strong>protein C resistance<\/strong>). Definitive diagnosis is made via genetic testing.<\/p>\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>Factor V Leiden<\/strong>&nbsp;is an autosomal dominant condition and is the&nbsp;<strong>most common<\/strong>&nbsp;cause of inherited hypercoagulability in Caucasians. Point mutations alter the cleavage site of factor V at locus Arg506, resulting in factor V that is<strong>&nbsp;resistant to degradation by protein C<\/strong>.<\/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\"><a href=\"http:\/\/xn--thorelli%20e,%20kaufman%20rj,%20dahlbck%20b-1vd.%20cleavage%20of%20factor%20v%20at%20arg%20506%20by%20activated%20protein%20c%20and%20the%20expression%20of%20anticoagulant%20activity%20of%20factor%20v.\/\" target=\"_blank\" rel=\"noreferrer noopener\">Thorelli E, Kaufman RJ, Dahlb\u00e4ck B. Cleavage of factor V at Arg 506 by activated protein C and the expression of anticoagulant activity of factor V<\/a><\/p>\n\n\n\n<p class=\"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-full\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"250\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/image_e6683f.png\" alt=\"Osmosis Let's get visual. Sign up now button.\" class=\"wp-image-2066\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/image_e6683f.png 700w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/image_e6683f.png?resize=300,107 300w\" sizes=\"auto, (max-width: 700px) 100vw, 700px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><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><\/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 breathing difficulties and chest pain. Labs show an elevated d-dimer. Purified protein C is added to the patient\u2019s plasma and causes no change in the lab values.&nbsp;Can you figure it out? [&hellip;]<\/p>\n","protected":false},"author":202,"featured_media":2063,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[27,20,1369,44],"tags":[],"class_list":["post-2062","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: Factor V Leiden - 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-factor-v-leiden\" \/>\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: Factor V Leiden - 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 breathing difficulties and chest pain. Labs show an elevated d-dimer. Purified protein C is added to the patient\u2019s plasma and causes no change in the lab values.&nbsp;Can you figure it out? [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\" \/>\n<meta property=\"og:site_name\" content=\"Osmosis Blog\" \/>\n<meta property=\"article:published_time\" content=\"2021-04-07T17:49:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-10-01T19:42:38+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/93.webp\" \/>\n\t<meta property=\"og:image:width\" content=\"1080\" \/>\n\t<meta property=\"og:image:height\" content=\"1080\" \/>\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-factor-v-leiden#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-factor-v-leiden\"},\"author\":{\"name\":\"Marina Horiates Kerekes, MD &amp; 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