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."

The number a laboratory would phone about is lower still. A 2025 survey gathered 50 lists of critical limits from university hospitals, Level 1 trauma centers, centers of excellence and other high-performing medical centers across the US. Forty-eight of those lists, 96 percent, published a low hemoglobin limit: the median was 6.0 g/dL and the range ran from 5.0 to 7.0. The authors note that these medians "have shifted away from thresholds associated with blood transfusion needs and severe thrombocytopenia", and they do not present that as reassuring. The same paper warns that shifting critical limits away from severe clinical thresholds "may delay detection of life-threatening conditions and the delivery of life-saving care for others". A silent phone is not evidence that you are fine. By our arithmetic on those published figures, a hemoglobin of 7.5 g/dL is severe anemia under WHO's cutoff, sits above the 7 g/dL restrictive transfusion threshold, and is higher than the top of the critical limit range in every one of the 48 lists that published one. Nobody is likely to call about it. That is not the same as it being fine. The guideline above already named two groups whose transfusion threshold is higher: 8 g/dL for preexisting cardiovascular disease, and 10 after a heart attack. Either way it needs a clinician within days rather than at the next routine visit. There is also no national list to check it against: CLIA requires a laboratory's own procedure manual to set out its "Imminently life-threatening test results, or panic or alert values" and never states what they should be. ARUP, one of the national reference laboratories, says as much in its own words: "Critical values are defined by the medical director of each technical section."

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.