Anaemia is common in patients with acute coronary syndrome (ACS) and is associated with significant recurrent bleeding risk and major adverse cardiovascular event (MACE). Esophageal-gastro-Duodenoscopy (EGD) is commonly used as an initial investigation for anaemia but is often non-diagnostic. Magnetically Controlled Capsule Endoscopy (MCCE) being less invasive and with comparable diagnostic accuracy as EGD, might be used as an alternative initial investigation for anaemia in patients with ACS.

Anaemia is common in patients with acute coronary syndrome (ACS) and is associated with significant recurrent bleeding risk and major adverse cardiovascular event (MACE). Esophageal-gastro-Duodenoscopy (EGD) is commonly used as an initial investigation for anaemia but is often non-diagnostic. Magnetically Controlled Capsule Endoscopy (MCCE) being less invasive and with comparable diagnostic accuracy as EGD, might be used as an alternative initial investigation for anaemia in patients with ACS.

Inclusion Criteria:

subjects are patients older than 18 years old with:

1. the diagnosis of ACS as defined by symptoms of chest pain or shortness-of-breath, abnormal electrocardiogram and positive enzyme, requiring coronary intervention
2. new-onset anaemia as defined by Hb<11 g/dL on admission blood taking

Exclusion Criteria:

1. History of active haematological disease including hemoglobinopathies such as thalassemia, Myelodysplastic syndromes, haematological malignancy, aplastic anaemia, or autoimmune haemolytic anaemia.
2. Patients with known active gastrointestinal malignancy.
3. Contraindications for CE: suspected or known gastrointestinal obstruction, stenosis, fistula, diverticula, presence of gastrointestinal obstruction symptoms such as pain or dysphagia; inoperative conditions or refusal to undergo abdominal surgery if required; history of laparotomy, gastric or bowel surgery; presence of metallic implants that is not MRI conditional.
4. Contraindications for EGD: Possible gastrointestinal perforation, medically unstable patients, patient with known pharyngeal diverticulum, and patients with recent head and neck trauma.
5. Inability to take 1-month DAPT such as non-deferrable surgery within 1 months, severe allergy or hypersensitivity reaction to aspirin or P2Y12 inhibitors, or patients in whom 1 months DAPT is not indicated.
6. Patients whose life-expectancy is less than 6 months.
7. Patients who are pregnant or lactating.
8. Patients who are unable to give informed consent.
9. Patients who are in active heart failure or fluid-overload state.
10. Patients who have chronic renal failure as defined by estimated glomerular filtration rate <15 ml/min/1.73m2.

Patients meeting eligibility criteria will be randomized by one of the research team staff via sealed envelopes with computer generated randomization number to one of the two study arms (0 for EGD, 1 for CE) in a 1:1 ratio, according to a central randomization scheme. Due to the nature of the interventions, researchers and patients are not blinded to group allocation.