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Blood and immune system diseases

Hemophagocytic lymphohistiocytosis (HLH)

A rare, potentially life-threatening disease in which the immune system becomes overactive and uncontrolled.

Not part of the panel of Türkiye's National Newborn Screening Programme (heel-prick test). Source

Prepare an emergency card

This page is translated from the Turkish original.

This disease is followed through the “Blood and immune system diseases” group.

Understanding the disease

This section has not yet been reviewed by a physician. It summarises patient information from sources such as MedlinePlus, Orphanet and the NHS in plain language. The disease can differ from person to person; talk to your doctor about diagnosis and treatment.

What happens in this disease?

In HLH, the immune system works excessively and out of control. This severe inflammation damages blood cells and organs. Familial HLH is inherited and often begins in infancy. Secondary HLH is more common; it is triggered by infections, cancer or immune diseases.

Which symptoms can occur?

HLH is a serious disease that can be life-threatening. The first symptoms can resemble other illnesses.

  • Long-lasting fever (common)
  • Enlarged liver and spleen (common)
  • Low blood cell counts; anemia, easy bruising and bleeding (common)
  • Skin rash and swollen lymph glands (sometimes)
  • Nervous system problems such as seizures or changes in consciousness (sometimes)
  • Difficulty breathing (sometimes)
  • Problems with liver and kidney function (sometimes)

How is it diagnosed?

For the diagnosis, the symptoms and a series of blood tests are assessed together. Blood counts, certain fats in the blood and the iron storage protein are checked. A bone marrow examination may be done. A genetic test is used to confirm the familial form.

Treatment and care

First, the overactive immune system is suppressed. For this, chemotherapy and medicines that suppress the immune system are used. Any triggering infection or illness is also treated. In familial HLH, a stem cell transplant is often done so that the disease does not come back. The doctor who follows the disease decides which treatment is suitable.

For the family: inheritance and genetic counselling

In familial HLH, one changed gene is received from the mother and one from the father; the risk is 1 in 4 in each pregnancy. Secondary HLH is often not inherited. In the familial form, genetic counselling and testing of family members are recommended.

Source: Orphanet — Hemophagocytic syndrome (ORPHA:158032) · MedlinePlus Genetics — Familial hemophagocytic lymphohistiocytosis · NORD — Hemophagocytic lymphohistiocytosis

Key facts

These facts are taken from Orphanet and MedlinePlus records (last checked: October 7, 2026). Frequency values are approximate ranges.

You are not alone: patient associations in Türkiye

Non-profit patient and family organizations in Türkiye working on this disease or disease group. Links are for information; Doktorclub is not affiliated with these organizations and does not endorse them.

We could not find a patient association specific to this disease.

For all rare diseases: Nadir Hastalıklar Federasyonu

Support and help

Doktorclub does not diagnose, recommend treatments or refer you to hospitals or doctors. These pages are meant to help you talk with your doctor.

News about HLH

Clinical trials (ClinicalTrials.gov)

A clinical trial is a regulated study that tests whether a new treatment is safe and whether it works, in patients who volunteer. Most trials look for a certain age, genetic change and health condition. Taking part is voluntary.

This list is not a treatment recommendation. Treatments tested in phase 1–3 trials are investigational (experimental): their efficacy and safety have not yet been proven and they are not approved treatments. Taking part depends on each trial’s criteria and a physician’s assessment; the first step is to talk to the doctor who manages your care.

Questions you can ask your doctor

  • Could this trial be suitable for us?
  • If we take part, how would current treatment and check-ups be affected?
  • Where does the trial take place, and how are travel and accommodation handled?
  • What happens if we want to leave the trial?

ClinicalTrials.gov lists 27 active interventional studies for this disease. 14 are recruiting now; none has a site in Türkiye. Last checked: October 7, 2026.

Selected records (studies with a site in Türkiye first):

See all studies on ClinicalTrials.gov · Joining clinical trials

Blood and immune system diseases: other news

Medical codes (for talking with your doctor and finding sources)

These codes identify the disease in international classifications and databases. They can help when you talk with your doctor or look for reliable sources.

International rare disease database: Orphanet

ICD-11 has a code only for the primary (familial) form: 4A01.23 (Primary haemophagocytic lymphohistiocytosis)

Codes checked against WHO ICD-11 and Orphanet on October 6, 2026.

This page provides general information and does not replace diagnosis or treatment. Talk to your doctor about symptoms, diagnosis and treatment.

The information on these pages is for general information only and does not replace medical advice. Talk to your doctor about diagnosis and treatment decisions. In an emergency in Türkiye, call 112.

Every update is based on an open source and labeled with its level of evidence. No advertising and no drug brand names. Our scientific principles

This page was translated from Turkish by the Doktorclub editorial team.