Hemoglobin Test — What It Measures and Why It Matters

What Is Hemoglobin, and Why Does It Matter?

Hemoglobin (Hb) is a protein inside red blood cells that carries oxygen from your lungs to every tissue and organ in your body — and carries carbon dioxide, a waste product, back to your lungs to be exhaled. It’s also what gives red blood cells their colour. A hemoglobin test simply measures how much of this protein is present in your blood, and it’s one of the most commonly ordered blood tests, usually as part of a Complete Blood Count (CBC).

What a Hemoglobin Test Can Reveal

• Before and after major surgery
• Blood in stool or vomit
• Chronic conditions like kidney disease or certain types of arthritis
• During pregnancy, to monitor for anemia
• Unexplained fatigue, weight loss, or headaches
• Heavy menstrual periods
• Monitoring during cancer treatment or medicines known to affect blood counts

Normal Hemoglobin Ranges

Adults:

• Men: 13.8 to 17.2 g/dL (138 to 172 g/L)
• Women: 12.1 to 15.1 g/dL (121 to 151 g/L)

Children:

• Newborn: 14 to 24 g/dL
• Infant: 9.5 to 13 g/dL

What Low Hemoglobin Can Mean

Low hemoglobin usually points to anemia, but the underlying cause can vary widely — from iron, folate, vitamin B12, or B6 deficiency, to bleeding, chronic kidney disease, bone marrow disorders, or pregnancy-related changes. A low reading is a starting point for further investigation, not a diagnosis on its own.

What High Hemoglobin Can Mean

Elevated hemoglobin is most often linked to low blood oxygen levels (hypoxia) over a prolonged period. Common causes include dehydration, smoking, certain heart or lung conditions, and in rarer cases, bone marrow disorders like polycythemia vera or a kidney tumour.