ABSITE 2026 Review: Hematology, Small Intestine, Vascular, and Colon Topics

Hematology and Coagulable Disorders

• 💡 The most common congenital hypercoagulable disorder is factor 5 Leiden, which is a resistance to activated protein C.
• ⚠️ Treatment for Heparin-Induced Thrombocytopenia (HIT) involves stopping heparin, using the four T's (thrombocytopenia, timing, thrombosis, other causes) for diagnosis, and starting an alternative anticoagulant like fondaparinux or argatroban.
• 💉 Vaccines for splenectomy patients should cover encapsulated organisms: H. flu, Strep pneumo, Neisseria meningitidis.
• 🩸 Reversal agents for anticoagulants include: platelets or desmopressin for aspirin/Plavix, protamine sulfate for heparin/Lovenox, idarucizumab for dabigatran, andexanet alfa for rivaroxaban/apixaban, and PCC or vitamin K/FFP for warfarin.

Interpreting Coagulation Tests (TEG)

• ⏱️ R time (rally time) indicates how long it takes for clot formation to begin; prolonged R time is corrected with FFP.
• 📈 The alpha angle and K time reflect the speed of clot formation and fibrin polymerization; they are addressed with cryoprecipitate.
• 🩸 Maximum amplitude (MA) measures clot strength and is improved by platelets.
• 📉 LY30 measures fibrinolysis, which can be impacted by TXA.

Small Intestine and Bowel Issues

• 🍎 Iron is primarily absorbed in the duodenum, while B12, bile, and folate are absorbed in the ileum.
• ⛓️ Short and medium-chain fatty acids are released directly into the portal circulation.
• ❓ Fistulas fail to close due to Foreign body, Radiation, Inflammation/infection, Epithelialization, Neoplasm, Distal obstruction, or Steroids (FRIENDS mnemonic).
• 🧳 Meckel's diverticulum, a true diverticulum, is associated with the rule of twos and can present with painless GI bleeding, intussusception, or appendicitis-like symptoms.
• 🧪 Carcinoid syndrome, often from small bowel tumors, produces serotonin and bradykinin, causing flushing and diarrhea if metastasized to the liver. Resection indications for appendiceal carcinoid tumors include size >2 cm, lymph node involvement, or positive margins.

Vascular Topics

• 🩺 Carotid artery stenosis intervention thresholds are >50% for symptomatic patients and >60-70% for asymptomatic patients.
• ⚡ Internal carotid artery peak systolic velocity >230 cm/s, an A-to-common carotid ratio >4, or ICA end-diastolic velocity >100 cm/s indicate >70% stenosis.
• 🗣️ The most common nerve injury after carotid endarterectomy is to the vagus nerve, causing hoarseness.
• 🏥 Stenting is preferred for high lesions, prior radiation, reoperative cases, or ipsilateral recurrent nerve palsy.
• 💔 Ascending aortic aneurysms are often due to cystic medial necrosis (Marfan's, Ehlers-Danlos), with repair thresholds at 5 cm for the ascending aorta, 6 cm for the descending thoracic aorta, 5-5.5 cm for AAA, 3 cm for iliac arteries, and all popliteal aneurysms.
• 🩸 Aortic dissection is classified by Debakey: Class I (ascending + descending), Class II (ascending only), Class III (descending only).
• 🚬 Smoking is the number one risk factor for AAA.
• 🕳️ Endoleaks are classified by type: Type I (proximal/distal seal), Type II (backflow from perforators), Type III (component connection), Type IV (graft porosity), Type V (unknown).
• 🚶 Surgical indications for peripheral arterial disease include critical limb ischemia (rest pain, ulcers, gangrene) or lifestyle-limiting claudication.
• 💡 Renal artery stenosis is typically atherosclerotic (left, proximal, men) or fibromuscular dysplasia (right, distal, women), often presenting as a "string of beads." Treatment is angioplasty and stenting.
• 🚫 The right renal vein cannot be ligated due to lack of collaterals, while the left renal vein can be due to collateral pathways (adrenal, gonadal).
• 🦵 Venous ulcers are primarily caused by incompetent valves leading to venous stasis.

Colorectal Cancer and Colon Topics

• 🎯 Colorectal cancer screening recommendations include colonoscopy every 10 years starting at age 45 for average risk, earlier for family history, and every 1-2 years for FAP.
• 🏥 Post-right hemicolectomy surveillance involves colonoscopies at 1, 3, and 5-year intervals.
• 🌊 Watershed areas in the colon are Griffith's point (splenic flexure) and Sudeck's point (rectosigmoid junction).
• 🧈 Butyrate (a short-chain fatty acid) is the main energy source for colonocytes.
• 🦠 Extraintestinal manifestations like anemia, arthritis, and ocular issues often improve with colectomy, while PSC and ankylosing spondylitis do not. Pyoderma gangrenosum improves in about half of cases.
• ⬆️ Internal hemorrhoids are graded I (no prolapse) to IV (irreducible prolapse).
• 🧑‍⚕️ Treatment for rectal prolapse includes laparotomy with rectopexy for good candidates or perineal approaches (Altemeier, Delorme) for others.
• ☢️ The protocol for squamous cell carcinoma of the anal canal involves neoadjuvant chemoradiation (5-FU, mitomycin) with salvage APR if needed.