RDW stands for Red (Blood Cell) Distribution Width, an index for the degree of variability in the size and shape of your red blood cells. Recent studies are showing it to be a powerful indicator of overall health and the risk of death from multiple causes. RDW is always included in the standard Complete Blood Count (CBC), one of the most routine lab tests in modern medicine, but there’s evidence that the usual lab reference range is too broad and it’s value is not widely appreciated. It has been established for some time that RDW predicts mortality form cardiovascular disease, but this study recently published in the Archives of Internal Medicine is particularly interesting because it shows that RDW predicts mortality in the general population independent of cardiovascular disease. The authors state:

“Higher RDW values were strongly associated with an increased risk of death…Even when analyses were restricted to nonanemic participants or to those in the reference range of RDW (11%-15%) without iron, folate, or vitamin B12 deficiency, RDW remained strongly associated with mortality. The prognostic effect of RDW was observed in both middle-aged and older adults for multiple causes of death.”

Two weeks later the another paper was published in the same journal on the same topic that begins with this observation:

“Red blood cell distribution width (RDW), an automated measure of red blood cell size heterogeneity (eg, anisocytosis) that is largely overlooked, is a newly recognized risk marker in patients with established cardiovascular disease (CVD).”

They set out to investigate

“the association of RDW with all-cause mortality and with CVD, cancer, and chronic lower respiratory tract disease mortality in 15,852 adult participants.”

Their conclusion:

“Higher RDW is associated with increased mortality risk in this large, community-based sample, an association not specific to CVD.”

Another paper just published in The Journals of Gerontology confirms these findings with an analysis of seven community-based studies of older adults. Their conclusion:

“RDW is a routinely reported test that is a powerful predictor of mortality in community-dwelling older adults with and without age-associated diseases.”

This paper just published in the journal Diabetes Care reports on the link between RDW, metabolic syndrome and cardiovascular disease: “A possible explanation for the observed association between RDW and MetS is that high RDW reflects an underlying inflammatory state that leads to impaired erythrocyte (red blood cell) maturation and anisocytosis (size variation), as suggested previously (1–3). In fact, MetS exacerbates oxidative and inflammatory stress in obese adults, which is a potential mechanism for the increased cardiovascular risk in this condition.”

And as you would expect, the European Journal of Heart Failure recently published a study on heart failure that compares RDW with N-terminal brain natriuretic peptide (NT-proBNP) in which the authors conclude:

“Red cell distribution width is a readily available test in the HF-population with similar independent prognostic power to NT-proBNP across the first to third quartiles. Prognostic models in HF (heart failure) should include RDW.”

And the ‘plot thickens’. In this paper published in the journal Digestive Diseases and Sciences the investigators observe:

“Impaired iron absorption or increased loss of iron was found to correlate with disease activity and markers of inflammation in inflammatory bowel disease (IBD). Red cell distribution width (RDW) could be a reliable index of anisocytosis with the highest sensitivity to iron deficiency.”

Their compelling conclusion:

“Among the laboratory tests investigated, including fibrinogen, CRP, ESR, and platelet counts…analysis indicated RDW to be the most significant indicator of active UC [ulcerative colitis]. For CD [Crohn's disease], CRP was an important marker of active disease.”

Lastly, you’ll appreciate the broadest statement yet about the value of this inexpensive and readily available marker. In a recent paper published in the Archives of Pathology & Laboratory Medicine. The authors begin by chiming in with the neighborhood chorus:

“A strong independent association has been recently observed between elevated red blood cell distribution width (RDW) and increased incidence of cardiovascular events;”

but they aim to

“assess whether RDW is associated with plasma markers of inflammation.”

Their conclusion:

“To our knowledge, our study demonstrates for the first time a strong, graded association of RDW with hsCRP and ESR independent of numerous confounding factors.”

In other words, RDW is inexpensive, easily obtained, and a powerful marker for inflammation in general, the common denominator of most chronic disease.

Here’s the ‘take home’ message (if you’ve gotten this far): If you have almost any blood work done at all it’s likely to include RDW automatically. Make good use of it, keeping in mind that laboratory reference ranges do not reflect the latest research and your doctor may not be aware of this. Functional medicine doctors want RDW to be no more than 13%.