Medical terms, defined.

Capillary refill time (CRT) is the time for color to return to a blanched distal capillary bed (e.g., nail bed) after pressure is applied for ~5 seconds. Normal is ≤2 seconds; prolonged CRT suggests poor peripheral perfusion from hypovol...

Thrombopoietin (TPO) is the primary hormone regulating platelet production. It is made mainly by the liver (constitutively) and acts on the c-Mpl receptor on megakaryocytes and hematopoietic stem cells to stimulate megakaryocyte growth a...

hCG is a glycoprotein hormone (α and β subunits) produced by syncytiotrophoblast cells of the placenta. It maintains the corpus luteum (and thus progesterone) in early pregnancy and is the basis of pregnancy tests (β-hCG detectable in bl...

Luteinizing hormone (LH) is a glycoprotein gonadotropin secreted by anterior pituitary gonadotrophs under GnRH control. In females, the mid-cycle LH surge triggers ovulation and corpus luteum formation; in males, LH stimulates Leydig cel...

FSH is a glycoprotein gonadotropin secreted by anterior pituitary gonadotrophs in response to pulsatile GnRH. In females it stimulates follicular growth and granulosa cell aromatase (estrogen production); in males it acts on Sertoli cell...

Triiodothyronine (T3) is the active thyroid hormone, ~3-4x more potent than thyroxine (T4). About 80% is made by peripheral conversion of T4 to T3 (by 5'-deiodinase), and the thyroid secretes the rest. It binds nuclear thyroid hormone re...

Capillary refill time (CRT) is the time for color to return to a blanched nail bed or skin area after firm pressure (~5 seconds) is released. Normal is ≤2 seconds (up to ~3 s in older adults/cold environments). Prolonged CRT suggests dec...

INR standardizes prothrombin time (PT) results across labs and reagents: INR = (patient PT / mean normal PT)^ISI. It monitors warfarin therapy (target usually 2–3) and assesses extrinsic/common pathway function and hepatic synthetic func...

Blood urea nitrogen (BUN) is the nitrogen content of urea in blood, a waste product of hepatic protein/amino acid catabolism (urea cycle) that is filtered by the kidneys. Normal is ~7–20 mg/dL. Elevated BUN suggests reduced GFR, prerenal...

The comprehensive metabolic panel (CMP) is a 14-analyte blood test assessing glucose, electrolytes, acid-base status (via bicarbonate), renal function (BUN, creatinine), calcium, and hepatic function (albumin, total protein, ALP, AST, AL...

A complete blood count (CBC) is a basic lab panel that quantifies red blood cells (RBC count, hemoglobin, hematocrit, RBC indices), white blood cells (total count, usually with differential), and platelets. It is the first-line test for...

The basic metabolic panel (BMP) is a blood test of 8 components: Na, K, Cl, HCO3 (CO2), BUN, creatinine, glucose, and calcium. It assesses electrolytes, acid-base status, renal function, and glucose, and it's one of the most commonly ord...

Elevated anion gap = AG (Na⁺ − [Cl⁻ + HCO₃⁻]) > ~12 mEq/L (normal ~8–12), indicating accumulation of unmeasured anions (e.g., lactate, ketoacids, toxins, uremic anions) in metabolic acidosis. Classic causes are remembered by the mnemonic...

McBurney point is the site of maximal tenderness in acute appendicitis, located one-third of the distance from the right anterior superior iliac spine (ASIS) to the umbilicus. It corresponds roughly to the base of the appendix. Tendernes...

An arterial blood gas (ABG) is a blood test from an arterial sample (usually radial artery) that measures pH, PaCO2, PaO2, HCO3-, and O2 saturation to assess oxygenation, ventilation, and acid-base status. Normal values: pH 7.35-7.45, Pa...

Rovsing sign is RLQ pain elicited by palpation of the LLQ (left lower quadrant), suggesting acute appendicitis. It is thought to result from retrograde displacement of colonic gas that increases pressure at the inflamed cecum/appendix, w...

The Bohr effect is the decrease in hemoglobin's oxygen affinity (rightward shift of the O2-Hb dissociation curve) caused by increased CO2 and/or decreased pH (increased H+). It promotes O2 unloading in metabolically active tissues and fa...

The Henderson-Hasselbalch equation relates pH to the pKa of a weak acid and the ratio of its conjugate base to acid: pH = pKa + log([A⁻]/[HA]). In physiology, it is used for the bicarbonate buffer system: pH = 6.1 + log([HCO₃⁻]/(0.03 × P...

A mixed acid-base disorder is the coexistence of two or more independent primary acid-base disturbances in the same patient (e.g., metabolic acidosis plus respiratory alkalosis). It is suspected when compensation is inappropriate (outsid...

Grey Turner sign is ecchymosis (bruising) of the flanks, indicating retroperitoneal hemorrhage. Classically associated with severe hemorrhagic (necrotizing) acute pancreatitis, though it can occur with other causes of retroperitoneal ble...

Babinski sign is dorsiflexion of the great toe with fanning of the other toes in response to stroking the lateral plantar surface of the foot. It indicates an upper motor neuron (corticospinal tract) lesion in adults; it is normal in inf...

Cullen sign is periumbilical ecchymosis (bluish discoloration) caused by retroperitoneal or intraperitoneal hemorrhage tracking to the umbilicus. Classically associated with hemorrhagic (necrotizing) acute pancreatitis, but also seen in...

Kehr sign is acute left shoulder pain (referred to the tip of the shoulder) caused by irritation of the diaphragm, classically from splenic rupture with intraperitoneal blood. It is worsened by lying supine or in Trendelenburg position a...

Brudzinski sign is a sign of meningeal irritation in which passive flexion of the patient's neck while supine causes involuntary flexion of the hips and knees. It suggests meningitis (or subarachnoid hemorrhage) but has low sensitivity (...

Kernig sign is a clinical sign of meningeal irritation: with the patient supine and the hip and knee both flexed to 90°, passive knee extension causes resistance or pain in the hamstrings and lower back. It is classically seen in meningi...

Janeway lesions are painless, nontender, erythematous or hemorrhagic macules on the palms and soles seen in infective endocarditis (classically acute, S. aureus). They are caused by septic microemboli with microabscess formation. They di...

Roth spots are retinal hemorrhages with a pale/white center, seen on fundoscopy. Classically associated with infective endocarditis (a minor Duke criterion, immunologic phenomenon), but nonspecific—also seen in anemia, leukemia, diabetes...

Osler nodes are painful, tender, red-purple subcutaneous nodules on the pads of fingers and toes, seen in infective endocarditis. They are thought to result from immune complex deposition (type III hypersensitivity) and/or septic microem...

Austin Flint murmur is a low-pitched, mid-to-late diastolic rumble heard at the cardiac apex in patients with severe aortic regurgitation. It is caused by the regurgitant jet impinging on the anterior mitral leaflet, causing partial clos...

A machinery (Gibson) murmur is a continuous, harsh, "rolling-thunder" murmur heard throughout systole and diastole, classically of patent ductus arteriosus (PDA). It peaks around S2 and is best heard at the left infraclavicular area/left...

The S3 gallop is a low-pitched extra heart sound heard in early diastole (~120–180 ms after S2) caused by rapid ventricular filling into a dilated or volume-overloaded ventricle. It is classically associated with systolic heart failure (...

Splinter hemorrhages are thin, linear, red-brown streaks under the nail, oriented longitudinally along the nail bed. Classically associated with infective endocarditis (a Duke minor/peripheral embolic-vascular phenomenon), but far more c...

A pleural friction rub is a coarse, grating, leathery adventitious breath sound caused by inflamed visceral and parietal pleural surfaces rubbing together during respiration. It is classically heard in pleurisy (pleuritis) and is associa...

A pericardial friction rub is a high-pitched, scratchy, grating ("leather-on-leather") sound heard when inflamed visceral and parietal pericardial layers rub against each other. It is pathognomonic for acute pericarditis and is best hear...

A V/Q scan is a nuclear medicine study that compares regional lung ventilation (inhaled radiotracer, e.g., Xe-133 or Tc-99m aerosol/DTPA) with perfusion (IV Tc-99m macroaggregated albumin). A "mismatch" (ventilated but not perfused segme...

A bone scan (radionuclide bone scintigraphy) uses Tc-99m-labeled diphosphonates (e.g., MDP/HDP) that adsorb onto hydroxyapatite at sites of increased osteoblastic activity and blood flow. It is highly sensitive but not specific for detec...

MRI (magnetic resonance imaging) uses a strong magnetic field and radiofrequency pulses to align and excite hydrogen protons, producing high-resolution soft-tissue images without ionizing radiation. It is the preferred modality for CNS,...

A barium enema is a fluoroscopic radiographic study of the colon in which barium sulfate (± air in double-contrast) is instilled rectally to outline the colonic mucosa. Classic findings: "apple core" lesion (colorectal carcinoma), "lead...

PET (positron emission tomography) is a nuclear imaging modality that uses positron-emitting radiotracers (most commonly 18F-fluorodeoxyglucose, FDG) to map metabolic activity in tissues. Areas with high glucose uptake (tumors, active in...

Fine needle aspiration (FNA) is a minimally invasive diagnostic procedure using a thin (typically 22–27 gauge) needle to aspirate cells (cytology) from a mass or lesion, e.g., thyroid nodule, lymph node, breast lump. It is the first-line...

An excisional biopsy is the complete surgical removal of an entire lesion (often with a small rim of normal tissue) for histopathologic diagnosis. It is the preferred approach for suspected melanoma and for small, well-circumscribed lesi...

Core needle biopsy (CNB) uses a large-bore (typically 11–18 gauge) cutting needle, usually under imaging guidance (US, stereotactic mammography, MRI, or CT), to remove cylinders of tissue that preserve architecture. It is the preferred i...

CABG is a surgical revascularization procedure that bypasses stenotic coronary arteries using autologous conduits (internal mammary artery, saphenous vein, radial artery) to restore myocardial blood flow. It improves survival over medica...

Sentinel lymph node biopsy (SLNB) identifies, removes, and examines the first lymph node(s) draining a primary tumor to stage regional nodal disease without a full lymph node dissection. It is standard in clinically node-negative breast...

Cerebrospinal fluid (CSF) is a clear, colorless ultrafiltrate-like fluid produced mainly by the choroid plexus ependymal cells of the ventricles. It cushions and buoys the brain, clears metabolic waste, and maintains a stable chemical en...

A chest tube (tube thoracostomy) is a flexible drain placed into the pleural space to evacuate air (pneumothorax), fluid (effusion, empyema), or blood (hemothorax) and restore negative intrapleural pressure so the lung can re-expand. It...

A central line (central venous catheter, CVC) is a catheter whose tip lies in a large central vein, usually the SVC near the cavoatrial junction, or the IVC for femoral lines. It is used for vasopressors, TPN, hemodialysis, long-term IV...

Percutaneous coronary intervention (PCI) is a catheter-based procedure that restores blood flow through stenosed or occluded coronary arteries using balloon angioplasty and usually drug-eluting stent placement. It is the preferred reperf...

An arterial line (A-line) is a thin catheter placed in a peripheral artery (usually radial) and connected to a pressure transducer for continuous, real-time beat-to-beat blood pressure monitoring and repeated arterial blood gas/lab sampl...

A Foley catheter is a flexible, indwelling urinary catheter held in the bladder by an inflated balloon (typically 5–10 mL sterile water) at its tip, allowing continuous bladder drainage into a collection bag. It is used for acute urinary...