Diagnostic tests for bacterial infections in older adults – unexpected results!

August 22, 2019

Kome Gbinigie, Maria Clark, Bernard Gudgin, Julia Hamer-Hunt

Older adults are more susceptible than younger people to bacterial infections. But there is evidence to suggest that they may not have typical symptoms when they get these infections. Clinicians often use blood and urinary tests to assist making a diagnosis. However, these tests may not work as well in older adults as they do in younger people.

How well do these different tests work in older adults?

Got the bug?

Researchers based at the University of Oxford searched the existing literature for studies. These studies assessed the ability of tests (blood, urinary and salivary tests) to diagnose a range of bacterial infections in older (65+ years) adults in general practice, emergency departments and outpatient clinics. The studies needed to give enough information to calculate a variety of diagnostic measures – such as how sensitive or specific a marker is in diagnosing a particular bacterial infection.

A marker of success?

Eleven studies were included in the review. Four of these studies assessed urinary tract infections (UTIs), a further four assessed blood-stream infection (bacteraemia), one study assessed intra-abdominal infections, and two studies assessed multiple bacterial infections grouped together. Seven of the studies were run in emergency departments; none was conducted in a GP surgery. The studies assessed how well blood and and urinary tests helped to diagnose different bacterial infections in older adults; none were found assessing the utility of tests on saliva.

The acid test – what was found?

A raised procalcitonin (PCT – a marker of bacterial infections) blood test helped to make a diagnosis of bacteraemia. An elevated C-reactive protein (CRP – a marker of inflammation) blood test at a level of ≥ 50mg/L only raised the chance of having bacteraemia by 5%. A positive urine dipstick result (for nitrites, white cells, or the two combined) helped to diagnose UTI in older adults; whereas a negative result helped to rule out a UTI. A blood test showing a raised white cell count was not particularly helpful in diagnosing infections in the abdomen (such as appendicitits or gallbladder infection). However, the review authors did find that having a raised blood white cell count may help to distinguish bacterial infections from other non-bacterial illnesses.

Testing times ahead…

More research is needed (please give us another research grant!) to make firm conclusions about which tests are helpful in diagnosing bacterial infections in older adults. It will be helpful if some of these studies are conducted in GP surgeries, which will make the findings more relevant to GPs. We would also like to find studies assessing a broad range of infections, such as chest infections. Until we have more research, clinicians will need to be heavily guided by the symptoms that an older adult presents with in order to make their diagnosis.

Read the full article here: https://bmcgeriatr.biomedcentral.com/articles/10.1186/s12877-019-1205-0

Authors:

Dr Kome Gbinigie (DPhil student and GP)

Ms Maria Clark (PPI contributor)

Dr Bernard Gudgin (PPI contributor)

Ms Julia Hamer-Hunt (PPI contributor)

Funding:

Jointly funded by the NIHR School for Primary Care Research (SPCR-2014-10043) and the Wellcome Trust. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.

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