The HLH medical abbreviation stands for hemophagocytic lymphohistiocytosis, a rare and serious condition in which immune cells become overactive, release large amounts of inflammatory signals and damage the body's own tissues. It appears in hematology, oncology, rheumatology and intensive care notes, often when a very sick patient has a persistent fever, an enlarged spleen and falling blood counts.
The long name breaks into parts. Hemo means blood, phago means eating, lympho refers to lymphocytes and histio to tissue macrophages, so it describes immune cells that multiply and can be seen engulfing blood cells. This page covers the two main types, the lab clues teams look for, and how HLH differs from the heart term HLHS.
At a glance
Stands for
Hemophagocytic lymphohistiocytosisMain types
Primary (familial, genetic) and secondary (acquired)Common triggers
Infections, especially viral; cancers such as lymphoma; autoimmune diseaseKey lab clues
Very high ferritin, low blood counts, high triglycerides, low fibrinogenUsed in
Hematology, oncology, pediatrics, rheumatology, ICUDo not confuse with
HLHS, hypoplastic left heart syndrome, a congenital heart defect
What happens in HLH
Normally, certain white blood cells switch on to fight an infection and then switch off. In HLH, that shutdown fails. T cells and macrophages keep activating one another and flood the body with cytokines, the chemical messengers of inflammation. The result is high fever, organ stress and destruction of blood cells.
Symptoms often look like a severe infection that does not improve: persistent fever, enlarged liver and spleen, rash, swollen lymph nodes, and sometimes confusion or seizures. Because it can progress quickly, clinicians who suspect HLH tend to involve specialists early.
Primary and secondary HLH
| Type | Who it affects | Usual cause |
|---|---|---|
| Primary (familial) | Mostly infants and young children | Inherited changes in genes that control immune cell killing |
| Secondary (acquired) | Children and adults | Triggered by infection, cancer, autoimmune disease or some immune therapies |
When secondary HLH happens with a rheumatologic disease, such as systemic juvenile arthritis or SLE, it is often called macrophage activation syndrome, written MAS. Among adults, lymphoma and viral infections are frequently cited triggers.
HLH medical abbreviation and the diagnostic criteria
A widely used set of diagnostic criteria counts eight features. Meeting five of them, or finding a known genetic cause, supports the diagnosis.
- Fever of about 38.5 C or higher
- Enlarged spleen
- Low counts in at least two blood cell lines
- High triglycerides or low fibrinogen
- Hemophagocytosis seen in bone marrow, spleen or lymph node
- Low or absent natural killer cell activity
- Ferritin of about 500 or more
- High soluble CD25, also called soluble IL-2 receptor
Ferritin in HLH is often far above that cutoff. Reference ranges differ between laboratories, and hematologists read every value against the whole clinical picture.
How it shows up in a chart
Progress note: "Persistent fevers, splenomegaly, plt 32, ferritin 18,400, concern for HLH, BM bx planned." The patient has ongoing fever, a large spleen, low platelets and a very high ferritin, and a bone marrow biopsy is planned to look for hemophagocytosis. These figures only illustrate how such a note is written.
Notes may also mention the HScore, a points based tool that estimates how likely reactive HLH is from fever, organ size, blood counts and several lab values. A high score prompts more testing rather than settling the question.
HLH versus HLHS
People searching for one term often land on the other. As a medical abbreviation, HLHS stands for hypoplastic left heart syndrome, a congenital heart defect in which the left side of the heart is underdeveloped and cannot pump blood to the body on its own. It is diagnosed before birth or soon after and is treated with a series of heart surgeries or transplant. It has no connection to the immune system disorder HLH.
The quickest clue is the setting: HLHS lives in pediatric cardiology and fetal echo reports, while HLH appears in hematology and ICU notes alongside ferritin and blood counts. Other heart defect pages include VSD and ASD.
Treatment in general terms
Treatment aims to calm the overactive immune response and remove the trigger. Common approaches include corticosteroids such as dexamethasone, the chemotherapy medicine etoposide, other immune targeted medicines, and treatment of the underlying infection or cancer. Primary HLH often requires a stem cell transplant. Care is usually led by hematology in a hospital with experience in the condition. For related blood and immune terms, see DIC, TTP and the diagnosis abbreviations list.
HLH is complex and every case is different. Questions about a specific diagnosis or treatment plan are best answered by the hematology team caring for the patient.
Frequently asked questions
What does HLH stand for in medicine?
HLH stands for hemophagocytic lymphohistiocytosis. It is a rare condition in which immune cells become overactive and damage organs and blood cells.
Is HLH a type of cancer?
No, but it can be triggered by cancers such as lymphoma, and some of its treatments, like etoposide, are also used in cancer care. It is managed by hematology and oncology specialists.
Is the HLHS medical abbreviation the same as HLH?
No. HLH is an immune system disorder, while HLHS is hypoplastic left heart syndrome, a birth defect in which the left side of the heart is underdeveloped. The extra S changes the meaning completely.
Why is ferritin checked for HLH?
Ferritin rises sharply in HLH, often to levels much higher than in most other illnesses. A very high ferritin with fever and low blood counts is a strong reason for doctors to consider HLH.