Haptoglobin
Also written as: Hp
A protein that binds free hemoglobin - it falls when red blood cells break down early.
What it measures
The level of haptoglobin, a protein made by the liver whose job is to bind hemoglobin released from destroyed red blood cells. Each bound complex is removed from circulation, so the level drops when red cells are being destroyed faster than usual.
Why a doctor orders it
It is a core part of the workup for hemolysis - red cells breaking down early - usually ordered alongside LDH, bilirubin, and a reticulocyte count when the cause of an anemia is being investigated. It is also checked when a reaction to a blood transfusion is suspected.
What is generally associated with a higher result
Broadly associated with inflammation and infection, because haptoglobin is an acute phase protein that rises whenever the body is inflamed, and with corticosteroid use. A raised value is rarely the finding of interest - the test is usually ordered to look for the opposite.
What is generally associated with a lower result
Broadly associated with hemolysis, where free hemoglobin consumes the available haptoglobin, and with liver disease, which reduces production. A small share of people inherit a low haptoglobin level without any disease behind it.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Recent inflammation or infection, which raises the level and can mask a fall
- Corticosteroids
- Estrogens, including oral contraceptive pills, which can lower it
- A recent blood transfusion
Questions to take to your appointment
- What did the LDH, bilirubin, and reticulocyte count show alongside this?
- Could recent inflammation be propping this value up and hiding a low result?
- Is an inherited low level a possibility worth considering?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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