Unit Converter
Haptoglobin
(Acute-Phase Glycoprotein – Key Marker for Hemolysis, Inflammation & Liver Function)
Synonyms
- Haptoglobin
- Hp
- Hemoglobin-binding protein
- Acute-phase α2-glycoprotein
- Hemopexin–related hemolysis marker (complementary test)
Units of Measurement
- µmol/L
- g/L
- mg/dL
- mg/100 mL
- mg%
- mg/mL
Key Conversions
(Molecular weight varies by phenotype; average ≈ 86 kDa)
1 g/L = 100 mg/dL
1 mg/dL = 0.01 g/L
mg% = mg/dL = mg/100 mL
1 mg/mL = 1000 mg/L = 1 g/L
µmol/L depends on exact molecular mass (~86,000 g/mol)
1 g/L≈11.6 µmol/L1\ \text{g/L} \approx 11.6\ \text{µmol/L}1 g/L≈11.6 µmol/L 1 µmol/L≈0.086 g/L1\ \text{µmol/L} \approx 0.086\ \text{g/L}1 µmol/L≈0.086 g/L
Description
Haptoglobin is a plasma glycoprotein synthesized by the liver.
Its main function is to bind free hemoglobin released during red blood cell destruction.
This prevents:
- Kidney damage
- Iron loss
- Oxidative injury
- Hemoglobin-mediated toxicity
Haptoglobin is a major acute-phase reactant and rises in inflammation.
Physiological Role
1. Hemoglobin Scavenger
Binds free Hb → forms Hb–haptoglobin complex → cleared by macrophages.
2. Protects Kidney
Prevents hemoglobin filtration & tubular toxicity.
3. Prevents Iron Loss
Recycles Hb-iron into the reticuloendothelial system.
4. Anti-oxidant Effect
Free Hb → oxidative stress
Haptoglobin minimizes Hb-driven oxidative injury.
Clinical Significance
LOW Haptoglobin (Most Important)
Primary marker for hemolysis
→ decreased because it is consumed by free hemoglobin.
Causes of Low Haptoglobin
1. Hemolytic Anemia (key diagnostic use)
- Intravascular hemolysis (most pronounced)
- Hemoglobinuria
- Hemoglobinemia
- DIC
- TTP/HUS
- PNH
- Transfusion reaction
- Mechanical hemolysis (prosthetic valves)
- Hemoglobinuria
2. Extravascular Hemolysis
- Mild decrease
- Seen in autoimmune hemolysis
3. Liver Disease
Reduced synthesis:
- Cirrhosis
- Hepatic failure
4. Congenital Anhaptoglobinemia
Genetic low or absent levels; benign but confuses interpretation.
5. Pregnancy
Mild reduction.
HIGH Haptoglobin
Occurs because it is an acute-phase reactant.
Causes:
- Infection
- Inflammation
- Trauma
- Stress
- Burns
- Malignancy
- Nephrotic syndrome
- Glucocorticoid therapy
High levels DO NOT rule out hemolysis
(because inflammation may mask lowering).
Reference Intervals
(Tietz 8E + Mayo + ARUP + BCSH Hemolysis Standards)
Adults
- 0.3 – 2.0 g/L
(= 30 – 200 mg/dL)
Children
- Lower in infancy
- Adult levels by ~1 year
Hemolysis Cutoffs
- <0.1 g/L (<10 mg/dL) → strong evidence for hemolysis
- Undetectable → intravascular hemolysis almost certain (unless liver failure)
Diagnostic Uses
1. Diagnose Hemolytic Anemia (Primary Use)
Interpret with:
- LDH ↑
- Indirect bilirubin ↑
- Reticulocytes ↑
- Hemoglobinuria
- Peripheral smear findings
- Direct antiglobulin test (DAT)
If:
- LDH high
- Haptoglobin low
→ hemolysis highly likely.
2. Monitor Hemolytic Disorders
Used in:
- Autoimmune hemolysis
- Microangiopathic anemia
- Transfusion reactions
3. Differentiate Hemolysis vs. Hemorrhage
- Acute blood loss → normal haptoglobin
- Hemolysis → low haptoglobin
4. Evaluate Liver Synthetic Function
Low in hepatic failure (reduced synthesis).
5. Detect Intravascular Hemolysis in Dialysis / ECMO
Mechanical RBC destruction → decreased haptoglobin.
Analytical Notes
- Serum or plasma
- Hemolysis during sample collection → invalid result
(because free Hb will falsely lower Hp) - Hp is stable, but avoid hemolyzed samples
- Acute inflammation may increase Hp significantly
- Genetic absence (0.1–0.3% population) may cause misleadingly low results
Clinical Pearls
- Low haptoglobin + high LDH = strongest biochemical signature of hemolysis.
- Inflammation may normalize haptoglobin even during hemolysis → interpret with CRP.
- In liver failure, haptoglobin falls because of reduced synthesis - mimic hemolysis.
- Hemoglobinuria strongly suggests intravascular hemolysis, not extravascular.
- Always interpret haptoglobin with complete hemolysis panel.
Interesting Fact
Haptoglobin polymorphisms (Hp1-1, Hp2-1, Hp2-2) influence antioxidant capacity, cardiovascular risk, and response to oxidative stress.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hemolysis Markers.
- BCSH Hematology Guidelines - Diagnosis of Hemolytic Anemia.
- AABB Standards - Hemolysis Evaluation.
- Mayo Clinic Laboratories - Haptoglobin.
- ARUP Consult - Hemolysis Workup.
- MedlinePlus / NIH - Haptoglobin Test.