The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, part 49

60. Is anaphylaxis the same as anaphylactic shock?

No. Anaphylaxis can result in anaphylactic shock but it often doesn’t. When talking about anaphylactic shock, people are referring to circulatory shock that was caused by anaphylaxis. Circulatory shock occurs when there is not enough blood to carry oxygen to all the tissues that need it. When the tissues don’t get enough oxygen, your organs stop working correctly.

Circulatory shock is usually caused by low blood pressure. Anaphylaxis commonly causes low blood pressure and that can cause shock. However, anaphylaxis does not always cause low blood pressure, and it does not always cause shock.

61. If a tryptase level over 10.9 ng/mL is high, why is one of the criteria for systemic mastocytosis a tryptase level of 20.0 ng/mL or higher?

Tryptase level is used in two ways in assessing mast cell patients: as a marker for activation, and as a marker for how many mast cells are in the body.

There are two primary methods of using tryptase to indicate mast cell activation.

The first way is to compare a tryptase level when a patient is reacting to a tryptase level when they are not reacting (baseline). Mast cells release more tryptase when they are activated. For mast cell patients, an increase of 20% + 2 ng/mL is considered evidence of mast cell activation. So if a patient has a baseline tryptase of 5 ng/mL when they are not reacting, anything 8 ng/mL (20% of 5 ng/mL is 1 ng/mL, then add 2 ng/mL = 8 ng/mL) or higher is considered evidence of activation.

The second way is to count anything over 10.9 ng/mL as evidence of activation.

When you are using tryptase as a measure of how many mast cells are in the body, the patient should not be reacting beyond their normal day to day symptoms. This is because you don’t want an increase in tryptase from activation to make the baseline level look higher than it is. Tryptase is used to measure how many mast cells are present because mast cells release some tryptase all the time, even when they aren’t activated.

Anything over 10.9 ng/mL is considered an elevation of tryptase. The reason that 20 ng/mL is the cutoff for the SM criterion is that patients are likely to have a positive bone marrow biopsy when the tryptase level is twice normal (21.8 ng/mL). They round the number down to 20 ng/mL because all tests have a margin of error. By rounding down to 20 ng/mL, they catch patients that might not have made the cutoff before because of an error in the test. This means that a patient who has a tryptase level of 20 ng/mL or higher is likely to have a bone marrow biopsy that will be positive for systemic mastocytosis.

For more detailed reading, please visit these posts:

Anaphylaxis and mast cell reactions

The Provider Primer Series: Mediator Testing

Patient questions: Everything you wanted to know about tryptase

The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, part 8