Diagnostics & workup:
- Pitting edema assessment with standardized grading: apply firm pressure over a bony prominence (medial malleolus, pretibial area, sacrum in bedridden patients) for 5-10 seconds; measure pit depth and rebound time; Grade 1+ (2mm, immediate rebound), 2+ (4mm, 15 sec), 3+ (6mm, 30 sec), 4+ (8mm, >30 sec); ALWAYS assess bilateral legs and compare; also assess for non-pitting edema (lymphedema, myxedema)
- BMP and serum albumin: creatinine/eGFR assess renal function; BUN/creatinine ratio distinguishes prerenal from intrinsic causes; electrolytes guide diuretic therapy; serum albumin <3.0 g/dL significantly reduces oncotic pressure and contributes to edema; severely low albumin (<2.0 g/dL) suggests nephrotic syndrome, liver failure, or severe malnutrition
- BNP or NT-proBNP: elevated levels (BNP >100 pg/mL or NT-proBNP >300 pg/mL) strongly suggest heart failure as the edema etiology; normal levels effectively exclude heart failure; very high levels (BNP >500) indicate severe heart failure; useful for differentiating cardiac from non-cardiac causes of bilateral edema
- Urinalysis and urine protein-to-creatinine ratio: assess for proteinuria (foamy urine) indicating nephrotic syndrome; proteinuria >3.5 g/day with hypoalbuminemia, edema, and hyperlipidemia defines nephrotic syndrome; urine sediment helps differentiate nephrotic (few cells, fatty casts) from nephritic (RBC casts, dysmorphic RBCs) syndromes
- Liver function tests and hepatic panel: AST/ALT, albumin, bilirubin, INR, and platelet count assess hepatic synthetic function; low albumin + elevated bilirubin + prolonged INR suggest cirrhosis; Child-Pugh score classifies cirrhosis severity and predicts prognosis
- Lower extremity duplex ultrasonography: MANDATORY for any NEW-ONSET UNILATERAL lower extremity edema to exclude DVT before assuming a benign cause; compression ultrasound is >95% sensitive for proximal DVT; also evaluates venous valve competence for chronic venous insufficiency diagnosis
- Echocardiography: if heart failure is suspected (elevated BNP, bilateral edema, dyspnea, orthopnea); assesses ejection fraction (HFrEF vs. HFpEF), diastolic function, valvular disease, right ventricular function, and estimated pulmonary artery pressure; guides treatment selection
Risk factors:
- Heart failure (left-sided or biventricular): the most common cause of bilateral dependent edema in clinical practice; elevated left ventricular end-diastolic pressure causes pulmonary congestion, and right-sided failure causes systemic venous congestion and peripheral edema; edema is a late finding reflecting significant fluid volume excess (typically 3-5 L excess before clinically detectable)
- Chronic kidney disease and nephrotic syndrome: CKD causes sodium and water retention leading to volume-dependent edema; nephrotic syndrome (proteinuria >3.5 g/day) causes severe hypoalbuminemia reducing plasma oncotic pressure, resulting in diffuse edema including periorbital edema (characteristically worse in the morning)
- Hepatic cirrhosis with portal hypertension: portal hypertension increases splanchnic capillary hydrostatic pressure causing ascites; decreased hepatic albumin synthesis reduces oncotic pressure; secondary hyperaldosteronism causes sodium retention; results in ascites, lower extremity edema, and hepatorenal syndrome
- Chronic venous insufficiency (CVI): incompetent venous valves cause ambulatory venous hypertension, increased capillary hydrostatic pressure, and chronic lower extremity edema; typically bilateral but may be asymmetric; characterized by hemosiderin deposition (brown discoloration), lipodermatosclerosis, and venous ulcers near the medial malleolus
- Medication-induced edema: calcium channel blockers (especially amlodipine -- precapillary vasodilation without matching venous dilation causes dependent edema in 5-30% of patients, dose-dependent); NSAIDs (sodium retention and prostaglandin inhibition); corticosteroids (sodium and water retention); pioglitazone (fluid retention); gabapentin/pregabalin (mechanism unclear)
- Lymphedema: obstruction or damage to the lymphatic system from surgical lymph node dissection (especially post-mastectomy), radiation therapy, malignancy (lymphoma, metastatic disease), or parasitic infection (filariasis -- most common cause worldwide); differs from other edema because it is NON-PITTING when chronic (fibrotic changes in tissue)
- Deep vein thrombosis: acute unilateral lower extremity edema that is an emergency requiring anticoagulation; DVT must be excluded in any patient with new-onset unilateral leg swelling before attributing it to a benign cause
