Hemoglobin Test

Hemoglobin is the protein in red blood cells that carries oxygen. A hemoglobin measurement may be requested on its own, but it is also commonly reported as part of a Complete Blood Count (CBC). The result should be interpreted using the reference interval on the laboratory report.

Haemoglobin (Hb) is the iron-containing protein inside red blood cells that carries oxygen from the lungs to tissues. The value is often requested as part of a CBC rather than as a stand-alone test because red-cell count, haematocrit and MCV help explain the pattern.

A low Hb value does not identify the cause of anaemia. Iron deficiency is one possibility, but blood loss, vitamin deficiency, chronic disease, kidney problems, inherited blood conditions and other causes may produce a similar result. A high value can also have several explanations, including reduced plasma volume or conditions associated with increased red-cell production. Clinical context and related tests matter.

A haemoglobin measurement may be requested when anaemia is suspected, when symptoms such as tiredness or breathlessness are being evaluated, during pregnancy-related care, or when a clinician is monitoring a known blood condition. It is often included inside a CBC rather than ordered alone.

Haemoglobin is interpreted together with age, sex, symptoms and often the rest of the CBC. A low result can occur with several different anaemia patterns, including iron deficiency, vitamin deficiency, blood loss, chronic disease and other causes. A high result can occur with dehydration, smoking, living at altitude or conditions that increase red-cell production. The haemoglobin number therefore tells a clinician that oxygen-carrying red-cell mass may be reduced or increased, but it does not identify the cause by itself.

MCV, ferritin, iron studies, vitamin B12/folate, kidney function or other tests may be added when the clinical question requires them. Trends are useful when previous results are available.

Haemoglobin is only one part of red-cell assessment. A value inside a population reference interval does not rule out every cause of tiredness, breathlessness or weakness, while a value outside the interval does not automatically establish a specific diagnosis. Hydration and several physiological factors can shift the concentration. The reporting laboratory's interval and the wider CBC pattern should be used for interpretation.

The test uses a venous blood sample, commonly in the same EDTA tube used for CBC. No fasting is needed for haemoglobin alone. If iron studies, glucose or lipids are being collected at the same time, follow the preparation for the combined order.