RCGP SCA Algorithm — UK Primary Care
Act immediately if any red flag present — do not proceed to routine work-up.
DVT is present in ~1 in 20 patients presenting with unilateral leg swelling in primary care; missing it risks fatal pulmonary embolism. Heart failure affects 920,000 UK patients and new presentations can deteriorate rapidly without diuresis. Pre-eclampsia carries a 3-fold increased maternal mortality risk if unrecognised. Nephrotic syndrome requires rapid urine dipstick — proteinuria ++ or +++ with oedema mandates same-day review. Always check both legs simultaneously to detect asymmetry.
Determine whether oedema is pitting/non-pitting, unilateral/bilateral, and acute/chronic. Pattern drives diagnosis.
Amlodipine is the commonest cause of bilateral ankle oedema in primary care — always check the drug chart before extensive investigation. The pitting/non-pitting distinction is the single most useful examination finding: non-pitting oedema essentially rules out cardiac/renal/hepatic causes. Bilateral oedema with normal cardiac/renal/hepatic function in an ambulant patient is idiopathic oedema until proven otherwise.
Classification drives the treatment pathway completely — a diuretic that helps cardiac oedema can worsen lipoedema and does nothing for lymphoedema. Venous insufficiency is the most common cause of bilateral ankle swelling in the community (prevalence ~10% over 65s). Stemmer's sign has 97% specificity for lymphoedema. Hypothyroidism is often missed because oedema is non-pitting and TFTs are not routinely ordered.
Raised JVP with ankle oedema has 70% sensitivity for heart failure — it is the most useful bedside sign. Pitting oedema requires 3–4L of excess fluid before it becomes clinically apparent. Checking weight serially is critical for HF management — patients should be taught to self-monitor and attend if gaining >2 kg in 2 days. Homan's sign has poor sensitivity/specificity for DVT and should not be used diagnostically.
NT-proBNP is the key gatekeeper test for heart failure — a result below cut-off has a 99% negative predictive value. D-dimer is only useful when Wells score is low-probability: it has 97% sensitivity but only 50% specificity. A negative D-dimer with low Wells score effectively excludes DVT without ultrasound, saving expensive imaging. TFTs are frequently omitted but hypothyroidism is present in 2–3% of patients with oedema.
The BNP/NT-proBNP pathway (NICE NG106) was designed specifically to streamline HF referral from primary care — using it correctly avoids both under-referral (missed HF) and over-referral (normal BNP). Lymphoedema must not be treated with diuretics — it worsens the condition by depleting intravascular volume, reducing lymphatic drainage further. ABPI measurement before compression therapy is mandatory — unrecognised PAD with compression causes limb ischaemia.
Furosemide reduces hospitalisation in acute decompensated HF but does not improve mortality — disease-modifying therapy (ACEI, beta-blocker, MRA) is what saves lives. Lercanidipine has 3-fold lower oedema incidence than amlodipine at equivalent doses. Rivaroxaban and apixaban are first-line DOACs for DVT (NICE TA354) with no requirement for overlapping heparin. Spironolactone reduces all-cause mortality by 30% in HFrEF (RALES trial) — do not withhold.
Leg elevation reduces capillary hydrostatic pressure by 30–40 mmHg — this is a measurable haemodynamic intervention. Salt restriction studies in HF show equivalent reduction in fluid retention to 20 mg furosemide daily. Calf pump exercises during air travel reduce DVT risk by 50%. Compression non-adherence is the leading cause of recurrent venous ulcers — patient education and practical aids (applicators, zip stockings) dramatically improve outcomes. Skin breakdown in lymphoedema leads to recurrent cellulitis which further damages lymphatics — a vicious cycle broken by good skincare.
Furosemide causes hypokalaemia in 10–40% of patients — early U&E check is mandatory, particularly in patients on digoxin (hypokalaemia increases toxicity). 3-month DVT anticoagulation review is a critical safety checkpoint — extending unnecessarily increases major bleeding risk by ~2%/year, but stopping too soon risks 5–10% recurrence. Unprovoked DVT warrants investigation for occult malignancy (CT chest/abdomen/pelvis) as 5% will have underlying cancer. Heart failure patients who gain >2 kg overnight should receive a rescue dose of furosemide.