Testing

First and foremost, a careful examination of the skin should be undertaken, looking for characteristic lesions of mastocytosis. If lesions are found, the physician should stroke the lesion firmly with a tongue depressor 5 or 6 times to see if it urticates (Darier’s sign). However, flushing and systemic low blood pressure can result from attempts to identify Darier’s sign in young children who have cutaneous mastocytoma or a polymorphic variant of maculopapular cutaneous mastocytosis with nodular lesions, such that this test should be avoided in these patients.^{1, 2} Darier’s sign is positive in almost all children and most of the adults who have skin involvement in mastocytosis. An international consensus task force of mast cell disease specialists has recently proposed that Darier’s sign be included as part of the major criterion for diagnosing skin involvement in mastocytosis patients.² Clear areas of skin can be stroked in the same way noted above to check for dermatographism, or skin writing, in which the area stroked becomes inflamed. Darier’s sign and dermatographism are characteristic cutaneous symptoms in mast cell diseases.

Information on tests for children with mast cell diseases is coming soon.

Tests for Mast Cell Activation and Mast Cell Activation Syndrome (MCAS)

An increase in the serum level of tryptase, above baseline and within a narrow (generally accepted as one to two hour) window of time after a symptomatic episode, is proposed as the preferred method for providing evidence of mast cell involvement.^3-5 An international consensus article provides a method for calculating the required minimum rise in serum tryptase:⁵

After a reaction, a level of serum tryptase that is a minimum of 20% above the basal serum tryptase level, plus 2 ng/ml, will meet the second criterion for a mast cell activation event. For example, if a patient had a basal (baseline level, at least 24 hours after a reaction) serum tryptase level of 8 ng/ml, a 20% rise, plus 2 ng/ml, would be 11.6 ng/ml. To meet the above criterion for serum tryptase, the patient would need a post-reaction serum tryptase level above 11.6 ng/ml. The calculation would be conducted as follows:

(8 ng/ml x 1.2) + 2 ng/ml = 11.6 ng/ml

(basal level, plus 20%) + additional 2 ng/ml = the serum tryptase level, after a reaction, that must be exceeded in order to meet a rise in serum tryptase considered a mast cell activation event

Consensus members also agreed that when serum tryptase evaluation is not available or when the tryptase level does not rise sufficiently to meet the required increase for the co-criterion, other mediator tests could suffice. A rise in urinary n-methyl histamine, prostaglandin-D₂, or its metabolite, 11β-prostaglandin-F_2α (24-hour urine test for any of the three), is considered an alternative for the co-criterion related to a requirement for a mast cell mediator level rise during a systemic mast cell activation event.^{5, 6} Some practitioners currently utilize other tests to make a diagnosis of mast cell activation. While we strongly recognize that we are limited in that there are many mast cell mediators, and yet we have commercial tests available for less than five of them here in the US, The Mastocytosis Society, Inc. (TMS) cannot endorse the use of other mediator markers as diagnostic tools until they have been adequately evaluated and proven as valid for mast cell diseases in sound, scientific research. TMS strongly supports and currently funds research to identify better markers for mast cell activation.

TMS does recognize, however, that capturing a mediator rise is not always easy, and depends on many factors, internal and environmental. We have seen 24-hour urine samples test negative simply because the lab technician did not refrigerate the sample in a timely manner (when the test was repeated and handled properly, the result was positive). Therefore, we support the use of a clinical diagnosis and advise that the patient continues to be treated when the following criteria have been met:⁷

• An exhaustive work-up has ruled out other medical conditions with similar symptoms and presentations
• The patient has exhibited consistent symptoms of mast cell activation in 2 or more organ systems during the same period of time, such as skin, gastrointestinal tract, central nervous system, etc.
• The patient responds to antimediator therapy
• The patient is monitored on a regular basis, with testing for mediator rises performed periodically, by a mast cell or other specialist and/or in conjunction with an established local allergist or other physician
• The patient is evaluated for other disease processes on an ongoing basis in order to be inclusive of any new changes in the patient’s condition

Routine and Follow-up Testing for MCAS

In patients who demonstrate a mediator rise, mediator testing should be repeated periodically. In addition, a complete blood count (CBC) with differential, blood chemistries, immunoglobulin levels, liver function tests, DEXA scans for bone density, and other testing may all be done as part of the routine exam, depending on the patient’s age, presenting symptoms, coexisting conditions and medication profile.⁸

Tests for Clonal Mast Cell Diseases Such as Systemic Mastocytosis or Monoclonal MCAS

Bone Marrow Biopsy

Standard technique can be used to obtain an iliac crest bone marrow biopsy and aspirate smear for diagnosis. Aspirated bone marrow should be allocated for flow cytometry to assess for the presence of mast cells with aberrant phenotype (i.e., co-expression of CD25). KIT mutation testing (see below) can also be performed on bone marrow aspirate. Immunohistochemistry for KIT, mast cell tryptase, and CD25 should be performed on sections of the biopsy.^{1, 9-12}

KIT Mutation Testing¹³

To understand why KIT testing is necessary, one must first understand the difference between clonal and non-clonal mast cell diseases. Clonal means that there is a defect in a person’s mast cell DNA, which results in their mast cells having abnormal characteristics. Although the most common defect seen in mast cell disease is KIT D816V, it is not the only one that can result in an abnormal disease process. Numerous other mutations in KIT have been associated with mastocytosis, and in the absence of a KIT D816V mutation, other testing can be performed to identify them, including KIT sequencing. If you have no change (no mutation, such as a KIT mutation) identified in your mast cell DNA, but experience mast cell activation, then you may have non-clonal disease, such as idiopathic mast cell activation syndrome.

There has been a peptide nucleic acid mediated PCR based test available for years that can identify the KIT D816V mutation in peripheral blood, and it has been able to detect the mutation in 44% of systemic mastocytosis patients tested.¹⁴ A newer test, an allele-specific oligonucleotide qPCR test, has proven to be much more sensitive and reliable. Patients with indolent systemic mastocytosis with skin involvement, for example, were found to have the KIT D816V mutation 92% of the time using the newer allele-specific qPCR blood test.¹⁴

Although the more sensitive test for the KIT D816V mutation (the allele-specific qPCR, with a sensitivity of 0.01%) that can be performed in peripheral blood samples has been developed, is not yet widely available here in the US. However, Mayo Clinic in Rochester, MN can perform the allele-specific oligonucleotide PCR (ASO-PCR) test for KIT D816V and the test may be available through several other labs in the US. Currently in the US, the result is often reported as either positive or negative, although in a research setting, results can be presented in more detail as an “allelic frequency”, which is essentially a measure of the extent to which the mutation is present versus KIT without that mutation (the allelic frequency can help in determining disease prognosis). It is important to note that receiving a negative test does not rule out a mast cell disease.^{13, 15} If an adult with systemic mastocytosis does not test positive for the KIT D816V mutation using sensitive testing methods, then sequencing of KIT might be considered.

Knowing the KIT mutation status can be very important when considering therapeutic options such as new medications and chemotherapy. The development of the allele-specific qPCR test will make peripheral blood KIT testing more widely available in the near future. More information on the use of KIT mutation testing in mast cell diseases (including potential use in prognosis and is available in published recommendations from the European Competence Network on Mastocytosis (ECNM).

Routine and Follow-up Testing for Systemic Mastocytosis (SM) and Smoldering SM

Examinations should occur periodically and include:¹³

• Dermatological exam (with stroking for Darier’s sign)
• Careful palpation of the liver, spleen and lymph nodes
• A full neuropsychological evaluation
• CBC with differential
• Serum tryptase and 24-hour urines for N-methyl histamine, prostaglandin D2 (PGD2), 11β-prostaglandin F_2α
• Liver function tests, serum albumin, serum LDH, and serum alkaline phosphatase¹⁶
• Blood chemistries
• Total immunoglobulins or total IgE, if indicated by previous testing
• DEXA scans for bone density; nuclear medicine bone scan, if indicated
• Bone marrow biopsy with flow cytometry and cytology, when indicated
• Allele-specific qPCR for KIT D816V mutation in peripheral blood/bone marrow, if not already performed; KIT sequencing, if indicated¹³
• CT scan/ultrasound, if indicated
• Other tests may be performed, as indicated, if there is a suspected hematologic disorder or to evaluate the individual patient’s symptoms.

NOTE: More information on the use of the above tests and examinations can be found in Table 3 of the ECNM recommendations.¹³ The Mastocytosis Society, Inc. has removed serum β2-microglobulin from the above list after a survey of some of our medical specialists indicated that this test is not routinely ordered to evaluate mastocytosis in the US.

Diagnostic Workup for Advanced Systemic Mastocytosis Variants or Associated Hematological Diseases^{1, 13, 17, 18}

When advanced disease or an associated hematological disorder is suspected, further evaluation of the patient beyond a bone marrow biopsy and aspirate with flow cytometry may include:

• Comprehensive bloodwork
• X-ray or CT scan of the chest, looking for evidence of significantly enlarged lymph nodes (greater than 2 cm in diameter)
• X-ray, nuclear medicine bone scan of the skeletal system, or bone density scan looking for osteoporosis, osteosclerosis, or areas where calcium has been completely lost from bone
• CT scan or ultrasound of the abdomen, looking for enlarged liver or spleen,¹⁶ enlarged lymph nodes, or the collection of fluid
• Endoscopy/colonoscopy and biopsy of the gastrointestinal tract, looking for evidence of mast cell infiltration, ulcers, or areas of bleeding. Mast cell infiltration can be identified by aggregates of 15 or more abnormal mast cells, or sheets of mast cells. Abnormal mast cells can be identified by the presence of CD25 on these cells.¹⁹
• Other tests may include next-generation sequencing and myeloid gene panels for additional genetic lesions.