Objectives: Determine indications and clinical utility of SARS-CoV-2 serology testing in adults TRANS and children TRANS. Design: Prospective evaluation of initial three weeks of a daily Monday to Friday pilot SARS-CoV-2 serology service for patients. Setting: Early post 'first-wave' SARS-CoV-2 transmission TRANS period at single centre London teaching hospital that provides care to the local community, as well as regional and national referral pathways for specialist services. Participants: 110 (72 adults TRANS, 38 children TRANS, age TRANS range 0-83 years, 52.7% female TRANS (n=58)). Interventions: Patient serum SERO from vetted referrals tested on CE marked and internally validated lateral flow immunoassay SERO (LFIA) (SureScreen Diagnostics) detecting antibodies to SARS-CoV-2 SERO spike proteins, with result and clinical interpretation provided to the direct care team. Main outcome measures: Performance SERO characteristics, source and nature of referrals, feasibility and clinical utility of the service, particularly the benefit for clinical decision-making. Results: The LFIA was deemed suitable for clinical advice and decision making following evaluation with 310 serum samples SERO from SARS-CoV-2 PCR positive patients and 300 pre-pandemic samples, giving a sensitivity SERO and specificity of 96.1% and 99.3% respectively. For the pilot, 115 referrals were received leading to 113 tests performed on 108 participants (sample not available for two participants); paediatrics (n=35), medicine (n=69), surgery (n=2) and general practice (n=2). 43.4% participants (n=49) had detectable antibodies to SARS-CoV-2 SERO. There were three main indications for serology; new acute presentations potentially triggered by recent COVID-19 infection MESHD e.g. PIMS-TS (n=26) and pulmonary embolism MESHD pulmonary embolism HP (n=5), potential missed diagnoses in context of a recent compatible illness (n=40), and making infection MESHD control and immunosuppression treatment decisions in persistently SARS-CoV-2 RNA PCR positive individuals (n=6). Conclusions: This study shows acceptable performance SERO characteristics, feasibility and clinical utility of a SARS-CoV-2 serology service using a rapid, inexpensive and portable assay for adults TRANS and children TRANS presenting with a range of clinical indications. Results correlated closely with a confirmatory in-house ELISA SERO. The study showed the benefit of introducing a serology service where there is a reasonable pre-test probability, and the result can be linked with clinical advice or intervention. Experience thus far is that the volume of requests from hospital referral routes are manageable within existing clinical and laboratory services; however, the demand from community referrals has not yet been assessed. Given recent evidence for a rapid decline in antibodies SERO, particularly following mild infection MESHD, there is likely a limited window of opportunity to realise the benefit of serology testing for individuals infected during the 'first-wave' before they potentially fall HP below a measurable threshold. Rapidly expanding availability of serology services for NHS patients will also help understand the long-term implications of serostatus and prior infection MESHD in different patient groups, particularly before emergence of any 'second-wave' outbreak or introduction of a vaccination programme.