Therapeutic drug monitoring (TDM) is the measurement of serum or plasma drug concentration to allow the individualization of dosing. We describe the case of a patient who was prescribed inappropriately large doses of vancomycin due to inaccurate TDM. Specifically, our laboratory reported progressively lower vancomycin concentrations despite dose increases. Eventually, when duplicate samples were sent to a different laboratory vancomycin concentrations were found to be in the toxic range. We hypothesize this was due to the patient generating immunoglobulin antibodies against her infection that interfered with the original TDM immunoassay. Immunogenic TDM interference has been known to rarely occur in patients with immune related comorbidities; however, if we are correct, this is a unique case as this patient did not have such a background. This case illustrates the importance of using clinical judgement when interpreting TDM as, in this case, substantial harm to the patient was likely only narrowly avoided.

The objective of this article is to test whether there is a significant difference in diagnostic accuracy between hospital and community-based ultrasound (US) for the detection of urinary calculi in the United Kingdom (UK). Materials and methods: A 30-month, single-blind, retrospective cohort study of all patients referred to Kent and Canterbury Hospital urology multidisciplinary meeting for suspected urinary calculi was conducted. Only those investigated with US and non-contrast computed tomography (NCCT, the gold standard) for their calculi were included. Concordance of US and NCCT was stratified by US location: i.e. either the hospital or community setting (e.g. the latter via general practitioners (GPs) or independent radiographers). Fisher's exact test was subsequently utilised to test for any significant difference between these two patient groups. Results: Of 2464 patients referred, 257 had both ultrasound and NCCT in their diagnostic workup. Of these, 150 and 107 patients had their US performed in hospital and community settings, respectively. No significant difference in the accuracy of US was detected between the two groups for the detection of urinary calculi when compared with NCCT. Conclusion: US carried out by independent radiographers and GPs in the community is just as accurate as US carried out by hospital sonographers for the detection of urinary calculi in the UK. Greater use of community US for the diagnosis of urinary calculi may promote greater patient/GP satisfaction and reduce hospital attendance without loss of diagnostic accuracy.