Iodine Starch Test Use in Pleuroperitoneal Leak

This is an observational study involving adult patients who are already undergoing a pleural fluid drainage procedure as part of their routine clinical care. The study is based on the results of a laboratory proof of principle experiment which the investigators performed in the NUH BioResource and Research \& Innovation Laboratory in November 2025, using non-clinical samples of standard peritoneal dialysis fluid to determine how much and what type of iodine is able to differentiate icodextrin from glucose or amino acid based peritoneal dialysis fluids. This has allowed the investigators to determine a clinical test in order to undertake an observational study of both non-dialysis patients who present to the pleural clinic (controls) and patients on peritoneal dialysis presenting with effusions to the renal unit, to ensure the iodine starch can be used in practice and that the test does not produce false positive results in patients with pleural effusions of other causes. The investigators will perform an observational control study in order to ensure that false positive results do not occur in pleural effusions of other causes. The investigators will consent 15 patients undergoing diagnostic or therapeutic pleural aspiration in the NUH pleural clinic. The sample size is an estimate based on the typical incidence of different pleural fluid types obtained in the NUH pleural clinic, and is expected to be sufficient to ensure we obtain samples of transudative, exudative and blood-stained effusion samples. The investigators will concurrently perform an observational study of patients on peritoneal dialysis who undergo diagnostic pleural aspiration (usually to investigate a possible pleuroperitoneal leak). The investigators will recruit five patients on peritoneal dialysis who present with pleural effusion to the Renal Home Therapies Unit. Up to five patients on peritoneal dialysis will also be recruited from two other UK centres. Potential participants will be identified by their usual clinical team when they attend the pleural clinic or renal service for a planned diagnostic or therapeutic pleural aspiration. Participants will consent for the investigators to collect 20mL of pleural fluid that is surplus to that required for clinical purposes. This will not require any changes to practice as it is standard clinical practice to remove larger volumes of fluid to relieve patients symptoms, and discard the waste fluid. The investigators add the pre-determined volume of Iodine and potassium iodide 2% (0.1mL) to 10mL of pleural fluid. The investigators will photograph the samples in the BioResource and Research \& Innovation Laboratory using a standard iPhone camera on an NUH provided work iPhone, and then discard the samples. The remaining 10mL will be frozen at -80oCin the BioResource and Research \& Innovation Laboratory to allow comparison of samples taken at different times, and reproducibility verification or collaborative validation with the other two renal units in the UK. Frozen samples will be kept for 2 years.

Following consent patients will be allocated a study number and pseudonomysed for completion of CRF. The investigators will collect demographic data (age, sex) and relevant past medical history (chronic kidney disease, chronic obstructive pulmonary disease, diabetes, heart failure, ischaemic heart disease, hypertension)from each recruit, results of biochemical tests conducted in NUH laboratories as part of their standard care, and diagnostic information.

Based on the outcome of the clinical study and the background laboratory studies the investigators will be able to validate recommendations about the volume and type of iodine needed to identify the presence of icodextrin in a pleural aspiration sample, which were demonstrated in the laboratory experiment.