Mastocytosis - Diagnosing mastocytosis

There are several tests available to confirm a diagnosis of mastocytosis, depending on which type you have.

Cutaneous mastocytosis

A physical examination of the skin is the first stage in diagnosing cutaneous mastocytosis – a form of the condition that's much more common in children than adults.

Your child’s GP or dermatologist (skin specialist) may rub affected areas of skin to see if they become red, inflamed and itchy (known as Darier’s sign).

A biopsy can usually be carried out to confirm a diagnosis. This involves removing a small sample of affected skin so that it can be checked under a microscope to see whether it contains an abnormally high number of mast cells.

Systemic mastocytosis

Five tests are commonly used to look for systemic mastocytosis. They are described below.

Full blood count (FBC)

A small sample of blood is taken and different types of blood cells in the sample are measured. Unusually low numbers of blood cells could be caused by excessive numbers of mast cells in your bone marrow.

Blood tryptase levels

The levels of an enzyme in your blood called tryptase are measured using a blood test. Tryptase is produced by mast cells and other cells.

Having more than 20 nanograms of tryptase in a millilitre of blood may suggest you have excessive numbers of mast cells in your bone marrow or other organs (it can also be raised by other conditions). A nanogram is a billionth of a gram.

Ultrasound scan

An ultrasound scan can be used to check whether your liver and spleen are swollen, which can occur in some cases of systemic mastocytosis.

An ultrasound scanner uses high-frequency sound waves to create an image of part of the inside of the body.

DEXA scan

A dual energy X-ray (DEXA) scan is a type of X-ray that measures the amount of calcium in bones.

Low levels of calcium are usually a sign that your bones have become weak and brittle (osteoporosis), which could be due to excessive numbers of mast cells accumulating inside your bones. Mast cells release substances that cause the bones to thin.

Bone marrow test

If the above tests suggest that you may have systemic mastocytosis, it's likely you'll be referred for a bone marrow test. You'll be given a local anaesthetic and a long needle will be inserted through your skin and into the bone underneath, usually in the pelvis.

The needle will be used to remove a small sample of bone marrow, which can be examined to see whether it contains an abnormally high number of mast cells.

The bone marrow can also be tested for the "kit mutation", which is known to be associated with most cases of systemic mastocytosis (see the causes of mastocytosis).