UK Biobank Study Links Hemoglobin Levels to Mortality

Published September 12, 2026, after an Annals of Internal Medicine study was published online September 8.

A prospective UK Biobank study found a U-shaped association between baseline hemoglobin concentration and long-term mortality. Mortality was lowest among participants whose hemoglobin was 1 to 3 g/dL above the World Health Organization thresholds used in the analysis, but the researchers said the findings should not define new anemia thresholds.

What the researchers measured

The cohort included 502,188 adults recruited in the United Kingdom from 2006 to 2010. Baseline hemoglobin was available for 477,876 participants, or 95.2% of the cohort. The median age was 58, 54.4% were women, and median follow-up was 13.6 years.

Researchers compared baseline hemoglobin with WHO sex-specific anemia thresholds: below 13.0 g/dL for men and below 12.0 g/dL for women. They then examined deaths from any cause, cardiovascular disease, and cancer. Analyses were divided by sex and by age younger than 60 versus 60 and older.

Hemoglobin is the oxygen-carrying protein in red blood cells and one of the measurements reported on a complete blood count (CBC). The study evaluated one baseline hemoglobin value rather than repeated measurements over time.

What the study found

All-cause mortality followed a U-shaped pattern. Risk was higher below the range associated with the lowest mortality, and it rose again at higher hemoglobin concentrations. The lowest all-cause mortality was observed 1 to 3 g/dL above the WHO thresholds.

Patterns for cardiovascular and cancer mortality were similar at low and borderline hemoglobin concentrations, although those associations weakened at higher concentrations. The results were also not uniform across every group. Associations were less consistent among women younger than 60 years.

These are population-level associations. The study did not establish that hemoglobin itself caused the difference in mortality, and it did not test whether changing a person's hemoglobin concentration changes health outcomes.

Why this is not a new target range

The WHO thresholds were category boundaries used by the researchers. They are not a new personal target from this study, and they are not necessarily the same as the reference interval printed on an individual laboratory report.

The authors described the findings as hypothesis-generating. Their conclusion says the results should not define new thresholds, although they may inform further research and clinical evaluation of borderline values.

Two limitations in the primary abstract matter. Hemoglobin was measured only once at baseline, so the analysis could not account for later changes. The study population was also predominantly White, which limits how confidently the results can be generalized to other populations.

Where CBC testing fits

A CBC reports hemoglobin alongside red blood cell count, hematocrit, red cell indices, white blood cells, and platelets. LabTestSuperstore's basic wellness panel also includes a CBC together with a comprehensive metabolic panel.

Those pages explain what the tests contain. The new study does not show that ordering a CBC more often improves outcomes, and it does not create a treatment rule for a value near a WHO threshold. A laboratory result still has to be read against the reporting laboratory's own reference interval and the broader clinical context.

What comes next

The paper provides a large, long-running dataset for studying hemoglobin and mortality, but it remains observational. Replication in more diverse populations and research using repeated hemoglobin measurements would help test how stable the association is and whether the same pattern appears elsewhere.

For now, the defensible takeaway is narrow: in this UK Biobank cohort, baseline hemoglobin and mortality were associated in a U-shaped pattern. That finding adds context to borderline values without redefining anemia or showing that changing hemoglobin will change mortality.

This article is editorial commentary and is not medical advice. It has not been reviewed by a physician and should not be used to diagnose a condition, set a target hemoglobin level, or make decisions about testing or treatment.