Primary HLH can be difficult to diagnose because many signs and symptoms are common to other illnesses. To diagnose primary HLH, doctors must rule out other illnesses, like infections or cancers, that could be causing symptoms.

Most people see many doctors before this rare disease is identified. If you or your loved one have been diagnosed, you may be wondering how the doctor figured it out.

Illustrated magnifying glass

What do doctors check for?

Genetic testing

  • Doctors use genetic tests to confirm whether someone has primary HLH. These tests can include targeted individual gene sequencing, HLH gene panel testing, and clinical whole-exome sequencing
  • Genetic tests can help determine if you or your loved one has certain gene mutations that cause primary HLH
  • It may take several weeks to get genetic testing results. Since it’s very important to treat primary HLH quickly, doctors may check for it another way using diagnostic criteria

Diagnostic criteria

If a person meets at least 5 out of the 8 criteria below, doctors may diagnose primary HLH:

  • Fever
  • Enlarged spleen
  • Lower numbers of blood cells (cytopenias)
  • A higher level of triglycerides and/or lower level of fibrinogen in the bloodstream
  • Higher levels of ferritin
  • Evidence that blood cells might be damaging other blood cells (hemophagocytosis) in certain areas of the body
  • Low levels of immune cells called “natural killer cells,” or none at all
  • Higher levels of sCD25, a molecule that increases with inflammation

Other medical tests

To help diagnosis primary HLH, your doctor may run additional tests, including:

  • Ferritin level testing
  • Bone marrow testing
  • Blood and liver function testing

Should other members of your family be tested for primary HLH? 

Because primary HLH may be inherited from parents, it may be a good idea to have other members of your immediate family tested.

Talk to your doctor or genetic counselor about potential next steps for your family.

Your doctor is your main source of medical information. Talk with your doctor to learn more about diagnosing primary HLH.