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Simple blood test a mortality predictor

Low lymphocyte levels can used as an indicator of an increased risk of mortality, US researchers say.

Lymphopaenia, readily measured through the common full blood count, has been shown to be associated with an increased likelihood of death from conditions such as heart disease, cancer and respiratory infections, according to a retrospective study published in JAMA Network Open.

This relationship was found to be consistent, independent of age, other serum immune markers and traditional clinical risk factors.

However, when patients with lymphopaenia also had other abnormal immune markers, namely elevated red cell distribution width (RDW) and a raised C-reactive protein (CRP), they ‘had a strikingly high risk of mortality’, the study authors said.

The study involved the analysis of data from the more than 31,000 participants (aged 30-63 years at baseline) who took part in the 12-year National Health and Nutrition Examination Survey (NHANES) in the US.

Researchers found relative lymphopaenia in 20.1% of the participants, while only 3.0% had severe lymphopaenia. Over the 12 year duration of this study, it was found that those people with relative lymphopaenia had a 30% increased risk of dying compared with people with a normal lymphocyte level. Severe lymphopaenia was associated with an 80% increased risk of dying from both cardiovascular and non-cardiovascular causes.

And if these people with a very low lymphocyte level also had other abnormalities of their haematological immune markers (elevated RDW and CRP), their risk of mortality was increased three fold.

“These data support the notion that immune status is indeed associated with resilience against cancer and cardiovascular disease, and an adverse immune phenotype may precede clinical manifestations of these illnesses,” the study authors said.

And this is the aspect of the study that seems to have got the researchers particularly excited; the fact that they appear to have identified a common, readily accessible biomarker to help predict which patients might most benefit further investigation and intervention to improve health outcomes down the track.

In an accompanying media release one of the study authors, US epidemiologist Dr Jarrod Dalton, said “the complete blood count test is convenient, inexpensive and, as our findings suggest may be used to help physicians screen for and prevent disease and disease-related mortality.”

The study authors do concede that what remains unknown is whether the low lymphocyte level is the result of the underlying developing disease process that will ultimately manifest in the life-limiting condition or whether it is perhaps the cause of the problem. This, they say, needs further research as both possibilities have plausible explanations.

Nonetheless, the researchers suggest the study can be considered to have important implications.

Clinicians can now utilise the lymphocyte count as an additional prognostic marker to help identify those patients at high risk of mortality.

Once identified, these patients can then be offered appropriate evidence-based disease preventive services such as cancer screening, vaccination, lifestyle changes and cardiovascular risk factor modification.

As the study authors say, this ‘may be a pragmatic, simple way to improve the effectiveness and efficiency of population health efforts.’

Reference

Zidar DA, Al-Kindi SG, Liu Y, Krieger NI, Perzynski AT, Osnard M, et al. Association of Lymphopenia With Risk of Mortality Among Adults in the US General Population. JAMA Netw Open. 2019; 2(12): e1916526. DOI: 10.1001/jamanetworkopen.2019.16526