The appropriateness of clinical microbiology laboratory investigations
: a retrospective study of the cost and clinical relevance of specimen management and processing

  • Yasin Abdi

Student thesis: Doctoral Thesis


Each year, NHS clinical laboratories carry out more than 700 million laboratory tests, of which 50 million are microbiology investigations. Several studies have shown that between 25% and 40% of all tests sent to the laboratory are unnecessary, and up to 46% of ordered microbiology tests are inappropriate. In light of these accounts, the present study was undertaken to evaluate the process of microbiology specimen management in order to assess microbiology test utilisation and the appropriateness of the test ordering processes. The study focussed on respiratory tract specimens using sputum microbiology as a model for the microbiology service inappropriate test utilisation.
The overall main aim of this study was to determine the appropriateness of clinical microbiology test utilisation, its clinical relevance and cost-effectiveness, hence recommend better utilisation strategies.
A total of 15,941 respiratory tract samples from Barts and The London NHS Trust were randomly selected from the years 2004/05 and analysed retrospectively. Seven hundred microbiology laboratory request forms from patients for whom respiratory tract cultures were requested over a three month period were examined in detail. These requests were derived from 511 sputum specimens, 100 throat swabs, 63 ear swabs and 76 samples from other respiratory tract sites. 641 (91%) of microbiology test requisition forms were completed, provided all requested details by the service users and were therefore considered as appropriate microbiology test requisitions. 660 (94%) of those examined stated the patient’s clinical diagnosis and only in 65 (13%) of these patients was the stated diagnosis as respiratory tract infection.
Sixty percent of sputum specimens examined were considered as poor quality. Forty percent of respiratory specimens were reported as culture positive, based on the local hospital criteria of microbiology test reporting. In sputum culture, 39% was reported as culture positive; however, less than 18% were positive with recognised respiratory pathogens, whilst 27% of throat swabs were reported as culture positive, of which 67% had throat pathogens. From the beginning of this study and before, there were no microbiology test comments and interpretation of test results provided with the test result reporting.
The test turnaround time of respiratory microbiology results reported within three days in 2004/2005 was only 20%. The total inappropriate respiratory specimens processed locally were 9,575. Extrapolating from our results, this suggests that 2,153,977 nationally were inappropriate in NHS hospitals in 2004/2005. The total cost of inappropriate respiratory microbiology test use was approximately £152,000 in local NHS hospitals. Extrapolating from our results, this suggests that £23,900, 000 nationally was the total cost of inappropriate tests in the NHS hospitals.
Following implementation of this study, follow up studies in 2006 and onwards indicated that there has been an improvement in the quality of the microbiology service. The number of good quality sputum specimens was 69% compared to 40% in 2004/2005. While the total microbiology test turnaround time that was reported within three days in 2009/2010 was more than 94%. From mid 2006 onwards, test interpretation comments have been used in all microbiology test result reporting. The total workload of respiratory tract microbiology activity decreased from 18,915/year to 16,651/year over the years 2004/2005 to 2007/2008, which is down nearly 8%.
Analysis of the findings showed that the usefulness of culture results was limited by the collection of inappropriate specimens, and lack of clinical information on the microbiology request form. The crucial importance of the role of clinical and nursing staff is stressed if the clinical relevance of sputum culture is to be maximised. The increasing introduction of electronic pathology test requests gives new opportunities to restrict the collection of inappropriate specimens and make substantial savings in resources, both in the ward and the laboratory. This type of study and audit can give invaluable information about the rationale behind testing, and the appropriateness of sampling and transport time. Appropriate measures for corrective actions can be identified.

Date of AwardSept 2011
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorGraham Mills (Supervisor)

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