Modern Practice of Diabetic Foot Sampling, Protocols, Pathways, Treatments and Techniques: an audit of specimen transport time from theatre to laboratory for diabetic foot tissue (MODAMP 2)

Introduction

The number of amputations secondary to diabetic foot infections continues to rise in the UK, with more than 185 diabetes-related amputations being carried out per week.¹ The 5-year mortality rates of patients with diabetic foot ulceration, minor or major lower limb amputations as a result of diabetic foot infections are 30.5%, 46.2% and 56.6%, respectively.² It is essential that we treat patients who present with this condition quickly and effectively. The UK Standards for Microbiology Investigations, published by Public Health England in January 2016, recommend that, where osteomyelitis is suspected, bone or soft tissue specimens taken from diabetic foot procedures should be processed within 2 hours to maximise chances of culturing causative organisms.³

Failure to achieve accurate microbiological sampling may result in delays to starting targeted antibiotic therapy, increased risk of recurrence and spread of infection and consequent higher risk of amputation with its associated morbidity and mortality. A recent review of diabetes and lower limb complications reported that specimens were sent from 50% of diabetic foot ulcer debridements, but that only 18% of cases of processed samples influenced antibiotic therapy.⁴ We aimed to investigate whether vascular networks within the Vascular Research Innovation Consortium (VaRICS) collected, transported and processed diabetic foot specimens within the 2-hour guideline.²

 

Methods

Four vascular networks (Black Country Vascular Network, Worcestershire Acute Hospitals NHS Trust, University Hospitals Birmingham and Shrewsbury and Telford Hospital NHS Trust) in the VaRICS were involved in this audit. The aim of the audit was to compare the sample rates against the published gold standard – the UK Standards for Microbiology Investigations – published by Public Health England in January 2016.³ Retrospective data on diabetic patients undergoing minor amputations between December 2021 and February 2022 were collated using an Excel proforma, with fields agreed by the leads for the data collection at the networks involved. These data were collected from paper and electronic patient notes, theatre records and electronic reporting systems. The data points collected were the date and time of the procedure, specimen collection time from theatre, specimen type (bone or tissue), transport medium and pathology receipt time. The time to processing was calculated as the time the operation ended to the time the laboratory reported receiving the specimen. The data were sent anonymously between sites using NHSmail and were analysed using descriptive statistics.

 

Results

A total of 129 procedures were performed during 3 months of data collection. Specimens were sent from 94 (73%) procedures. Of the 94 specimens taken, 21 (22%) reached the laboratory for processing in <2 hours with a mean time of 10.5 hours. Fifteen (29%) samples taken ‘in hours’ were processed in <2 hours, with a mean time of 7.51 hours, and six (14%) samples taken ‘out of hours’ were processed in <2 hours with a mean time of 14.4 hours. Table 1 shows the number of specimens taken and the time taken for processing.

The transport medium or lack of transport medium was recorded in 54 (61%) samples; 78% of bone and tissue samples were transported in no medium. In the remaining samples the transport medium was either not collected or a beaded (n=1) or amines (n=2) transport medium was used.

 

Discussion

Overall, we can see that, compared with the recent report on diabetes and lower limb complications, the West Midlands theatre sampling has a higher specimen collection rate than the published literature (77% compared with 50%).⁴ However, the number of samples processed within 2 hours is only 42%. Out of hours, this is likely due to insufficient staffing to transport the samples and receive them at the laboratory to commence processing. In hours, the gold standard remains for all samples to reach the laboratory within the 2-hour window to start processing.³ This means increased awareness within theatres and by microbiology laboratory technicians about the importance of processing specimens and pre-emptively alerting the team during the theatre briefing.

The guidelines of the UK Standards for Microbiology Investigations advise that samples collected in theatres should be placed in a sterile leak-proof container with Ringer’s or saline solution and then into a sealed plastic bag.³ None of the samples taken in this study were processed in this way, demonstrating a need for education in this area.

To standardise this measurement of time within the study, we used the end of the operation as the specimen collection time. This is a limitation of the study design. This study was carried out in multiple networks, and it was not possible to identify storage conditions of the samples prior to transportation to the laboratory. This may affect the quality of the samples upon arrival at the laboratory, but would be an interesting avenue for further investigation. The National Institute for Health and Care Excellence (NICE) guidance states that, in patients with suspected diabetic foot infections, microbiology samples should be taken to aid with diagnosis and treatment.³ We do not know exactly how taking these samples affects the duration of antibiotic treatment. This is an area of research still to be undertaken.

 

Conclusion

The Society of Vascular Surgery states that “In patients at high risk for diabetic foot osteomyelitis, we recommend that the diagnosis is most definitively established by the combined findings on bone culture and histology”.⁵ Ensuring our samples are processed correctly will lead to a quicker diagnosis of osteomyelitis, accurate antibiotic treatment and better patient outcomes. The recent James Lind Alliance exercise put accurate diabetic foot sampling and its consequent treatments at points 2 and 4 on its priority list,⁶ whilst the recent NHS Resolution document emphasises the importance of getting it right first time with diabetic foot disease as the costs of problems that develop are not inconsequential to the NHS and must be considered.⁴