Hemoglobin under 8 g/dL

WHO defines severe anemia as a hemoglobin under 80 g/L (8.0 g/dL) in adults 15 to 65, below 60 percent of the cutoff under its 1989 rule; the guideline notes that recalculating the old cutoffs put severe at "between 62 and 70%." WHO says nothing about treatment at this level beyond the remark that management depends on cause. The clinical bodies do.

Where 8 comes from in practice. The number that makes this band different is the transfusion threshold, and it belongs to hospitalized patients, not to a lab result read at home. The 2023 AABB international guideline: "for hospitalized adult patients who are hemodynamically stable, the international panel recommends a restrictive transfusion strategy considering transfusion when the hemoglobin concentration is less than 7 g/dL," adding that clinicians "may choose a threshold of 7.5 g/dL for patients undergoing cardiac surgery and 8 g/dL for those undergoing orthopedic surgery or those with preexisting cardiovascular disease." The AABB's 2025 guideline for acute myocardial infarction points the other way for that one group: a liberal strategy "when the hemoglobin concentration is less than 10 g/dL," because "A restrictive strategy of 7 to 8 g/dL may result in increased mortality in patients with AMI." Both guidelines say the decision incorporates clinical context, never the number alone. The NHLBI's plain version: "Transfusions help people with serious anemia quickly increase the number of red blood cells in their blood."

What else the bodies say. The BSG: "Limited transfusion of packed red cells may on occasion be required to treat symptomatic IDA, in which case IRT is still necessary post-transfusion." A transfusion treats the count, not the cause. Parenteral iron is considered early when "the correction of IDA is particularly urgent," and the urgent GI investigation recommended for any unexplained iron deficiency anemia applies with more force here, since the BSG ties the likelihood of "serious underlying GI pathology" to the degree of anemia. The NHLBI adds that "Surgery may be needed to stop internal bleeding."

What a reader should do with this result. Not wait for a routine follow-up. The NHLBI says more serious iron deficiency anemia may cause tiredness, shortness of breath or chest pain, lists dizziness and fainting among anemia's general symptoms, and its complications list runs to heart failure. WHO's table is the definition; the AABB, BSG and NHLBI text above is what a clinician will be weighing the same day.