Unit Converter
Hemoglobin (HGB)
(Primary Oxygen-Carrying Protein – Core Marker for Anemia, Polycythemia & Oxygen Transport Capacity)
Synonyms
- Hemoglobin
- Hb / Hgb
- Blood hemoglobin
- Total hemoglobin concentration
- Oxygen-carrying protein
Units of Measurement
- g/L
- g/dL
- g/100 mL
- g%
- mg/mL
Key Conversions
1 g/dL = 10 g/L
1 g/100 mL = 1 g/dL
g% = g/dL
1 mg/mL = 1 g/dL
1 g/L = 0.1 g/dL
Description
Hemoglobin (Hb) is a tetrameric protein in red blood cells containing heme + globin chains, responsible for:
- Transporting oxygen from lungs to tissues
- Transporting CO₂ from tissues to lungs
- Maintaining acid–base balance
Hb concentration is one of the most essential parameters in the complete blood count (CBC).
Physiological Role
Hemoglobin performs several vital functions:
1. Oxygen Transport
Each Hb molecule binds 4 oxygen molecules through iron (Fe²⁺).
2. Carbon Dioxide Transport
~20–25% of CO₂ is carried as carbaminohemoglobin.
3. Buffering & Acid-Base Balance
Hb binds H⁺ ions, maintaining pH.
4. Blood Viscosity & Tissue Perfusion
Hb concentration influences blood viscosity and oxygen delivery.
Clinical Significance
LOW Hemoglobin (Anemia)
The most common clinical abnormality.
Major Causes
1. Blood loss
- GI bleeding
- Menorrhagia
- Trauma
- Surgery
2. Nutritional Deficiency
- Iron deficiency (most common worldwide)
- Vitamin B12 deficiency
- Folate deficiency
3. Hemolysis
- Autoimmune hemolytic anemia
- G6PD deficiency
- Sickle cell disease
- Thalassemia
- Mechanical hemolysis (prosthetic valves)
4. Bone Marrow Disorders
- Aplastic anemia
- Leukemia
- Myelodysplastic syndromes
5. Chronic Diseases
- CKD
- Infections
- Chronic inflammation
6. Pregnancy
- Physiologic hemodilution
HIGH Hemoglobin (Polycythemia)
Causes
1. Polycythemia Vera (PV)
- JAK2 mutation
- Increased RBC mass
2. Chronic Hypoxia
- COPD
- Obstructive sleep apnea
- High altitude
- Congenital heart disease
3. Secondary Erythrocytosis
- Renal tumors (EPO-producing)
- Hepatocellular carcinoma
- Exogenous EPO
- Testosterone and anabolic steroids
4. Relative Polycythemia
- Dehydration
- Burns
- Severe vomiting
Reference Intervals
Adults
| Group | Hemoglobin |
| Men | 130 – 170 g/L (13.0–17.0 g/dL) |
| Women | 120 – 150 g/L (12.0–15.0 g/dL) |
Children
- Newborns: 140–200 g/L
- 1–2 months: 100–180 g/L
- Older children: approach adult ranges
Pregnancy (WHO anemia thresholds)
- 1st trimester: <110 g/L
- 2nd trimester: <105 g/L
- 3rd trimester: <110 g/L
Critical Values
- <70 g/L (7 g/dL) → risk of ischemia, heart failure
- >200 g/L (20 g/dL) → hyperviscosity, thrombosis
Diagnostic Uses
1. Diagnose & Classify Anemia
Hb is the primary diagnostic parameter.
2. Polycythemia Evaluation
High Hb → evaluate for:
- JAK2 mutation
- Hypoxia
- EPO excess
3. Monitoring Illness & Therapy
- Iron therapy
- B12/folate treatment
- CKD anemia on ESA therapy
- Chemotherapy toxicities
4. Pre-operative Assessment
Hb guides transfusion strategy.
5. Athletic Performance / Doping
High Hb suggests:
- Blood doping
- EPO use
- Altitude training
Analytical Notes
- Measured via automated hematology analyzers (cyanmethemoglobin or colorimetric)
- Hemolysis or lipemia may interfere with some methods
- Point-of-care Hb devices are widely used (trauma, ICUs, field medicine)
- Always interpret with hematocrit, RBC count, and indices (MCV, MCH, MCHC)
Clinical Pearls
- Hb is often 3 × hematocrit/10, but hydration affects this rule.
- Iron deficiency is the most common cause of low Hb worldwide.
- Very high Hb (>18 g/dL in men) strongly suggests polycythemia vera or chronic hypoxia.
- Smoking increases Hb due to chronic CO exposure.
- Hb cannot diagnose hemoglobinopathies alone - electrophoresis required.
Interesting Fact
Hemoglobin carries 1.34 mL of oxygen per gram, meaning a normal adult with 15 g/dL Hb transports ~1 L of oxygen per minute at rest.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hematology.
- WHO Criteria - Diagnosis of Anemia.
- AABB Transfusion Guidelines.
- BCSH Hematology Standards.
- Mayo Clinic Laboratories - Hemoglobin.
- ARUP Consult - Anemia & Polycythemia Workup.
- MedlinePlus / NIH - Hemoglobin Test.