Issue 40 / 19 October 2015

GPs should maintain a high threshold for requesting cardiac troponin testing and promptly refer patients with suspected acute coronary syndrome, according to researchers.
 
A prospective cohort study of 124 GP-initiated cardiac troponin (cTn) tests, published in the MJA, found that based on clinical risk factors, 71 of 104 patients (69%) were at high or intermediate risk of acute coronary syndrome (ACS). It also found that 69 of 124 patients (55.6%) had typical ischaemic pain and 62 of 124 patients (50.0%) were tested within 48 hours of symptom onset ACS. (1)
 
While 122 of the 124 cTn results in the study were negative, the researchers said it did not rule out the possibility of ACS, with 3.7% of patients (13/355) admitted to hospital with an ACS within 30 days of receiving a negative result.
 
“Possible ACS is one setting in which GPs can justifiably advise patients to present to a hospital, rather than undertaking investigations in primary care”, the researchers said.
 
Professor Mark Nelson, chair of the discipline of general practice at the University of Tasmania, said the researchers’ conclusions were warranted and considered.
 
He told MJA InSight that, like any diagnostic test, the agility of cTn testing depended on pre-test probability. “If there is a high pre-test probability [of ACS], there’s really no sense in doing the test.
 
“If someone has typical chest pain, if it’s not stable angina, they should go to an emergency department, because they’re the ones who need acute care.”
 
Professor Nelson said ordering the test, often based on a patient request, where there was low clinical suspicion of ACS was also not useful in primary care.
 
“If [the result] does come back marginal, then it’s unlikely to indicate clinical disease and it’s just going to confuse matters.”
 
The MJA researchers wrote that GPs might not fully understand the limitations of cTn testing, as 23.4% of tests in their study were ordered within 12 hours of symptom onset, “at which point the test may be insufficiently sensitive”.
 
“While all major guidelines groups recommend serial testing to exclude ACS in this context, no serial testing was performed by GPs in our study”, they wrote.
 
In many cases, the test result did not alter patient management.
 
The researchers also highlighted the difficulties faced by GPs in dealing with patients with suspected ACS.
 
“The consequences of missing an ACS diagnosis can be grave, yet there are no reliable clinical predictors of ACS, and primary care investigations have their limitations. At the same time, GPs have an important role as gatekeepers of the health system”, they wrote.
 
Professor Nelson agreed that GPs were often in a difficult situation and were sometimes criticised for ready referral, but the stakes were high in cases of suspected ACS.
 
“If people have clinical symptoms or signs of having an ACS, it’s not something that should be managed in primary care, except in certain rural and remote circumstances, which isn’t discussed in this paper”, he said.
 
The researchers included only samples collected at urban practices, acknowledging that rural and regional practices were likely to have different approaches to cTn testing.
 
Professor Derek Chew, director of cardiology at Southern Adelaide Local Health Network, said general practices managing patients with suspected ACS needed to develop models of care to effectively deal with the results of cTn testing.
 
“If you embed tests into a practice that is not designed to deal with the result of the test, this is what you are going to see”, he said of the MJA research findings.
 
“I am not saying that primary care can’t do this; I am saying that primary care needs to be designed to do this if they want to do it.”
 
Professor Chew, who coauthored an MJA editorial last year about the potential for cTn and the challenges of its use in primary care, said the diagnostic tests were a very effective tool in assessing chest pain when used within an appropriate model of care. (2)
 
He said GPs initiating cTn testing for patients presenting with chest pain should be able to provide and interpret electrocardiograms for all patients who presented with chest discomfort, chase cTn results in a timely manner and repeat assays as required.
 
Protocols for patients with positive test results and for those with negative results but with high suspicion also needed to be programmed into the system, Professor Chew said.
 
 
 
(Photo: Jarun Ontakrai / shutterstock)