Diagnostic Tests and Risk Factors

There are many different diagnostic tests, including serum tryptase, plasma histamine, specific IgE-level measurements, and skin tests. However, all of these tests have their pitfalls.

An elevated tryptase level 1 - 6 h after a suspected anaphylactic reaction indicates mast cell degranulation. Together with a suggestive history and clinical findings, this supports the diagnosis of anaphylaxis (Fisher and Baldo 1998). However, serum tryptase concentration may be normal even in fatal anaphylaxis.

Plasma histamine level reaches a peak within 15-30 min of the onset of anaphylaxis and returns to baseline values within 1 h. This test is therefore of very limited use and only helpful in some patients.

Diagnosis of Serious or Fatal Reaction to Contrast Media

During anaphylaxis/anaphylactoid reaction, histamine is released from both basophils and mast cells, while tryptase is absent from basophils but released from the granules of mast cells together with histamine. New highly reliable assays are becoming available for measuring tryptase and histamine in plasma (Laroche et al. 1998). Tryptase's half-life is about 90 min, and the best time for measuring is 1 - 2 h after the reaction (not later then 6 h). Only very high concentrations of serum tryptase should be regarded as specific for fatal anaphylaxis/anaphylactoid reactions (Brockowet al. 1999). Histamine has a very short half-life (approximately 2 min), and the best time for measuring its plasma level is between 10 min and 1 h after the reaction. Consequently, blood samples for histamine analysis should be drawn as soon as possible after the reaction. For tryptase, blood sampling 1 - 2 h after onset of the symptoms has been recommended. To enable comparison with baseline levels, new blood samples should be collected 1-2 days after the reaction (Brockow et al. 2005a).

The level of histamine release has been demonstrated to have a direct relationship to the severity of the immediate reaction to iodinated contrast media (CM) (Laroche et al. 1998). The proof of an increased hista-mine or tryptase level during the acute reaction can help to diagnose an anaphylactic reaction, even retrospectively.

Muscle relaxants and natural rubber latex are very significant and potent allergens in the perioperative period. In patients with a suspicious history, a search for specific IgE antibodies can be done prior to the operation to minimize the risk of a potential anaphylactic reaction (see Sects. 4.8 and 4.9). If a latex allergy is suspected, a skin prick test is recommended (see Sect. 4.9).

In suspected penicillin incompatibility, a prior skin test might be very helpful, because it has a high negative predictive value (see Sect. 4.8).

All patients with an anaphylactic reaction should undergo an consultation with an allergy and immunology specialist, and the results documented in an allergy

4.5 Prevention and Treatment of Anaphylactic Reactions

card. After a severe reaction, the patient should be taught to do initial self-treatment in the event of contact to the allergen. In such cases, patients should therefore carry an emergency kit with them. This should include an Hl-antagonist (e.g., dimetindene maleat, 2 ml = 2 mg) as a liquid and an quick effective corticosteroid in a liquid form (e.g., celestamine liqui-dum, 5 ml = 0.5 mg betamethasone) or for inhalation (e.g., Primatene mist epinephrine) and an adrenaline pen for self- intramuscular injection (e.g., Fastjekt or EpiPen, 0.3 ml = 0.30 mg epinephrine).

Generally, all patients with a history of asthma or atopy (including hay fever and food allergies) have an increased risk of anaphylactic/anaphylactoid reactions in the perioperative interval. Risk factors have been clearly demonstrated for two major allergens commonly found in hospital:

1. Although reactions to iodinated radiographic CM are not true allergic ones, patients with a history of a previous reaction to contrast material have a three-to fourfold greater risk of subsequent reaction than the general population (Katayama et al. 1990; Mor-cos and Thomsen 2001). Other important risk factors include asthma and a history of atopy, including hay fever and food allergies, increasing the risk of anaphylaxis eight- to tenfold (Morcos and Thomsen 2001; Shehadi 1982). In addition, patients treated with -adrenergic blockers and interleukin-2 are at increased risk of acute adverse reactions to CM (Thomsen et al. 2004; Morcos 2005) (see Sect. 4.7).

2. The risk of latex hypersensitivity in patients who require chronic bladder care (e.g., individuals with bladder extrophy or meningomyelocele) has been reported to be as high as 72% (Ricci et al. 1999). The risk of anaphylaxis in the operating room is 500-fold greater in patients with spina bifida as compared with control groups (Taylor and Erkek 2004). In individuals of occupations with regular exposure to latex gloves (e.g., health care workers, hair dressers, cleaners, housekeepers) the incidence of latex sensitization is up to 12 %, compared to 1 % - 6 % in the general population (Lieberman 2002) (see Sect. 4.9).

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