Home Biomarkers HDW (Haemoglobin Distribution Width)

HDW (Haemoglobin Distribution Width)

Anemia Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Anemia

Overview

Haemoglobin Distribution Width (HDW) is a red‑cell index that quantifies the variation in haemoglobin concentration among individual erythrocytes. It is derived from the haemoglobin concentration histogram produced by automated haematology analysers and reflects how uniformly haemoglobin is distributed across the red cell population. HDW is used in the assessment of anaemia to help distinguish iron‑deficiency anaemia, mixed nutritional anaemias, chronic disease, and haemoglobinopathies. Symptoms prompting testing include fatigue, pallor, shortness of breath, dizziness or other signs of anaemia. HDW reference limits can vary by analyser and lab; small age or sex differences exist, though major differences are uncommon.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Included in: Anaemia profile/complete blood count with red cell indices.
Symptoms prompting test: persistent fatigue, pallor, breathlessness, easy bruising or abnormal bleeding.
Diagnostic/monitoring use: helps detect and classify types of anaemia (e.g., iron deficiency, mixed deficiencies, thalassaemia) and monitor response to therapy.
Causes of abnormal levels: iron deficiency, recent bleeding, haemoglobinopathy, mixed nutritional deficiencies, recent transfusion or recovery from marrow suppression.
Biological meaning: increased HDW = greater heterogeneity of haemoglobin content among RBCs; decreased HDW = unusually uniform RBC haemoglobin content or analyser/artifact.
Lifestyle/family history: poor diet, chronic blood loss (NSAID use, menstruation), family history of thalassaemia/haemoglobin disorders may prompt testing.

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Understanding Test Results

Values within 2.5–3.5 g/dL: considered typical; suggests relatively uniform haemoglobin content across red cells.
Mildly elevated (≈3.6–4.5 g/dL): indicates increased heterogeneity and can be seen early in iron‑deficiency anaemia, mixed iron/Vitamin B12 or folate deficiencies, or recovering marrow after treatment.
Correlate with MCV, RDW, ferritin, transferrin saturation and clinical history.
Markedly elevated (>4.5 g/dL): suggests significant anisocytosis of haemoglobin content common with established iron deficiency, chronic blood loss, mixed anaemias, haemoglobinopathies or post‑transfusion mixed populations; warrants iron studies and haemoglobinopathy testing as indicated.
Low values (<2.5 g/dL): uncommon and may reflect a very uniform RBC population (for example after recent homogeneous transfusion), analyser artifact or pre‑analytic issue; interpret cautiously and repeat if unexpected.
Always interpret HDW together with CBC indices (MCV, MCH, MCHC, RDW), reticulocyte count and iron/B12/folate studies and correlate with clinical exam; abnormal HDW is a clue, not a standalone diagnosis.

Normal Range

2.5-3.5 g/dL

FAQs

Q: What is the HDW hemoglobin distribution width?

A: HDW (hemoglobin distribution width) is a lab index that measures variability in hemoglobin concentration among individual red blood cells. Higher HDW indicates greater heterogeneity and helps detect and classify anemias commonly raised in iron‑deficiency, mixed nutritional deficiencies, hemolysis, recent transfusion, or bone‑marrow disorders. It’s interpreted alongside other CBC indices (MCV, MCHC, RDW) to guide diagnosis and monitor treatment.

Q: How to calculate HDW?

A: HDW (hemodialysis dry weight) isn’t calculated by a single formula; it’s the post-dialysis weight where the patient is euvolemic no edema, stable blood pressure, clear lungs, and no intradialytic hypotension or symptoms. Clinicians find it by gradual weight adjustments, monitoring BP, symptoms, physical exam and weight trends, and using objective tools like bioimpedance or lung ultrasound, with regular reassessment.

Q: What happens if RDW is high?

A: A high RDW means increased variation in red blood cell sizes (anisocytosis). It commonly signals nutritional-deficiency or mixed anemias (iron, B12, folate), recent blood loss, hemolysis, chronic inflammation, or marrow disorders. Clinically it suggests impaired oxygen delivery and prompts further testing—CBC indices, iron studies, B12/folate, reticulocyte count—and evaluation for underlying causes by a clinician.

Q: What is HDW in medical terms?

A: HDW commonly refers to Hedyotis diffusa Willd, a traditional Chinese medicinal herb (also called Oldenlandia diffusa). It’s used for inflammation, infections and as an adjunct in some cancer therapies; active constituents include iridoids, flavonoids and alkaloids. Preliminary studies show anti‑inflammatory, antimicrobial and antitumor effects, but clinical evidence is limited and safety, dosing and interactions require medical supervision.

Q: What is the value of RDW in thalassemia?

A: RDW in thalassemia is usually normal or only mildly elevated. In thalassemia trait, RDW typically remains within the normal lab range (about 11.5–14.5%), whereas RDW may be higher in thalassemia major or when there’s concurrent iron deficiency or recent transfusions. An RDW >15% more commonly indicates iron deficiency or a mixed picture rather than isolated thalassemia trait.

Q: What diseases cause high RDW or HDW?

A: High RDW or HDW indicates increased variation in red blood cell size or hemoglobin and is seen in iron‑deficiency anemia, vitamin B12 or folate deficiency, recent or ongoing hemolysis or bleeding, mixed anemias, myelodysplastic syndromes, chronic liver disease and alcohol use, post‑transfusion states, chronic inflammation, and some hemoglobinopathies and bone‑marrow disorders.