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Lewis Yaxley awarded Gillian Nicholls Prize

March 15, 2023

Congratulations to Kellogg’s Lewis Yaxley on being awarded this year’s Gillian Nicholls Prize for his MSc in Evidence-Based Healthcare dissertation. Lewis’ research looks at improving diagnosis for potentially life-threatening sudden gastrointestinal bleeding.

The Gillian Nicholl Prize is awarded by the Department of Evidence-Based Healthcare, to a student whose dissertation they deem to be outstanding.

On receiving the prize, Lewis said ‘I would like to thank my supervisor, Dr Jason Oke for his valuable guidance throughout the dissertation as well as former fellow MSc classmates Sean Godfrey and Ali Mulhem for acting as second reviewers for study screening and methodological quality evaluation respectively. My sincere thanks again to the college and prize donor for the generous award’.

Read a summary of Lewis’ dissertation:

The accuracy of computed tomography angiography compared with technetium-99m labelled red blood cell scintigraphy for the diagnosis and localisation of acute gastrointestinal bleeding: a systematic review & meta-analysis

Computed tomography angiography (CTA) and technetium-99m labelled red blood cell scintigraphy (RBCS) are two diagnostic imaging tests commonly used to evaluate patients presenting with suspected acute gastrointestinal bleeding. CTA is a radiological test that has been in clinical use for the evaluation of gastrointestinal bleeding since the early to mid 2000s and has several favourable characteristics such as ease of access and speed of imaging. RBCS is a nuclear medicine test that has been in clinical use since the 1980s. It is often considered to have a superior detection threshold for bleeding but suffers from the drawback that it does not provide cross-sectional images of the body (it provides two-dimensional planar images only), although augmentation with modern techniques known as single photon emission computed tomography (SPECT) and hybrid SPECT/CT may overcome this shortcoming. Despite RBCS being in clinical use for over four decades there has been no published systematic review on its diagnostic performance. There also remains ongoing controversy regarding which modality is more accurate in detecting and localising bleeding.

Therefore, the purpose of this dissertation was to perform a systematic review of the comparative diagnostic performance of these two imaging tests. The review made use of recently developed methodological tools to assess risk of bias and certainty of evidence specifically adapted to comparative test performance. These are extensions of well-known tools (QUADAS and GRADE) commonly used to assess methodological quality of primary studies and certainty of evidence related to questions concerning single test accuracy.

The review also employed some relatively simple statistical techniques in an attempt to overcome challenges associated with evaluating evidence where there is missing data, specifically that related to patients that do not go on to have further testing or evaluation (e.g. endoscopy or surgery) which is necessary to validate the results of imaging.

The review identified 58 studies investigating CTA and/or RBCS. Meta-analysis of a suitable subset of these provided evidence that both tests have similar sensitivity (a measure of the ability of a test to designate an individual with a disease or condition as positive) and specificity (the ability to designate an individual without a disease or condition as negative) for detecting acute gastrointestinal bleeding. However, CTA is superior to RBCS for localising the precise source of the bleeding (noting RBCS still performs to a relatively high level). The evidence, however, was considered low or very-low certainty due to high risk of bias across studies and reliance predominantly on comparisons of primary studies which evaluated a single test. There was insufficient evidence to conclude whether the addition of modern cross-sectional imaging techniques (SPECT or hybrid SPECT/CT) improves the diagnostic performance of planar scintigraphy.