What is the impact of regular monitoring with specific blood tests in people with long term conditions on patient outcomes? Trial emulation using routinely collected primary care data. EBED Conference 2024

It is generally accepted that people with long term conditions benefit from regular monitoring after diagnosis. However, the evidence base for the optimal monitoring strategies, including which test should be used at what frequency, is weak. Current practice is largely based on expert opinion and local protocols vary, which has led to substantial variation in blood test use within the UK. We aim to investigate whether regular monitoring in people that have recently been recently diagnosed with type 2 diabetes mellitus (T2DM), hypertension, or chronic kidney disease with certain blood tests impacts health outcomes using routinely collected primary care data.

We are developing analyses to emulate a target trial using primary care electronic health records from Clinical Practice Research Datalink (CPRD) and Hospital Episode Statistics (HES). We are using a sequential trial approach to estimate the effects of regular testing with commonly used blood tests (including liver function tests, renal function tests, and lipid profile) on patient outcomes. We will compare patients who have received regular testing with the candidate test to patients who have not received these tests. The primary outcomes are events that could be prevented with regular monitoring such as unplanned hospital admissions. We will censor patients when they deviate from their assigned strategy, pooling data from the trials to use pooled logistic regression to calculate outcome cumulative incidence and risk difference. Time-varying confounding will be accounted for by applying time updating inverse probability weights.

We are developing the analysis to evaluate the effects of monitoring liver function in patients with newly diagnosed T2DM. Patients were eligible if they had a T2DM diagnosis and HbA1c record within 30 days of diagnosis between 2004 and 2019, were not pregnant during the study period, and had no history of liver disease. 47,344 patients were eligible for recruitment, and were recruited on the date of their first HbA1c test 12 weeks after diagnosis . Patients were assigned to the testing strategy compatible with their data on this date. 28,993 patients had liver function testing on this date and were assigned to the intervention group, and 18,351 people did not have liver function testing and were assigned to the control group. Eighty percent of people in the control group and 56% of the intervention group switched monitoring strategy during follow-up and were censored.

We aim to apply these methods to other test and condition combinations once finalised, and use these findings to decide whether to recommend regular monitoring with certain blood tests in patients with T2DM, hypertension, or chronic kidney disease. Challenges developing these methods include accounting for residual confounding, high censoring rates, and limitations associated with routine data.