Wed3November0844PM 4

A patient becomes hypotensive and develops a widespread urticarial rash following the administration of Augmentin. Anaphylaxis is suspected and he receives appropriate treatment.

Which single test is the most appropriate marker of mast cell degranulation in these circumstances?

(Please select 1 option)

Alpha-protryptase

Tryptase Correct

Beta-tryptase

Histamine

N-methylhistamine

Explanation

Mast cells are found within many tissues including lung, intestine and skin. Tryptase is a protease enzyme which acts via widespread protease activated receptors (PARs). Mast cell tryptase is a reliable marker of mast cell degranulation.

Take blood samples (5-10 ml clotted blood) for mast cell tryptase as follows:

Initial sample as soon as feasible after resuscitation has started - do not delay resuscitation to take the sample

Second sample at one to two hours after the start of symptoms

Third sample either at 24 hours or in convalescence.

Histamine can be measured by fluorometric assays, radioenzymatic assays, and immunoassays. These methods have been applied to plasma and urine to detect histamine that had been released in vivo and to release histamine in vitro from basophils and mast cells.

Another mast cell constituent is tryptase, which is a more selective marker of mast cells, because negligible amounts are found in basophils.

ß-Tryptase is stored in secretory granules and is actively released when mast cells degranulate.

a-Protryptase remains in the proenzyme form and is constitutively released from mast cells, and consequently its level in serum reflects total numbers of mast cells.

Because histamine has a half life of only one minute it is difficult to measure reliably.

N-methylhistamine (NMH), the major metabolite of histamine has a longer half life and can be measured in a 24 hour urine sample following a reaction.

Reference:

Harper NJ, et al. Suspected anaphylactic reactions associated with anaesthesia. Anaesthesia. 2009;64:199-211.

Answer Statistics

1

2%

2

90%

3

8%

4

2%

5

1%

Times answered: 279