Will Platelet-Activating Factor (PAF) be the "BNP" of Anaphylaxis?

Brain Natriuretic Peptide (BNP) was a new test when I started my internship and the NEJM had just published a study showing that it might help physicians diagnose CHF exacerbation. I remember my seniors arguing during journal club that the new BNP test had a limited value and CHF exacerbation would always be a clinical diagnosis. I begged to disagree by pointing out that clinical examination would have its place but nobody should ignore such a simple (and cheap) diagnostic helper as BNP which would be a first-line diagnostic test in near future.

Several short years later, and now most patients with SOB (shortness of breath) get a bedside BNP in the ER soon after the chief complaint is written by the triage nurse. BNP has become as important in rapid diagnosis of CHF exacerbation as troponin is in diagnosis of chest pain and acute coronary syndrome.

The push for biochemical markers will always be there because physical diagnosis is time-consuming and there is variability between different providers. For example, Dr. B's "rales" may sound like "crackles" to Dr. C. I cannot emphasize enough the importance of physical examination but on the other hand, no sensible physician will ignore a rapid and useful lab test.


Platelet-Activating Factor (PAF). Image source: Wikipedia, GNU Free Documentation License.

Platelet-Activating Factor (PAF) may become the "BNP" of anaphylaxis in the future -- a laboratory test which greatly helps in diagnosis. The analogy between PAF and BNP also comes from the fact that both tests help stratify the severity of the disease. The higher then BNP, the more severe the CHF exacerbation is. The same rule applies to PAF.

According to a study published in the NEJM, serum PAF levels were directly correlated with the severity of anaphylaxis. The proportion of subjects with elevated PAF levels increased from 4% in the control groups to 20% in the group with grade 1 anaphylaxis, 71% in the group with grade 2 anaphylaxis, and 100% in the group with grade 3 anaphylaxis (P less than 0.001).

PAF acetylhydrolase is the enzyme that inactivates PAF. Not surprisingly, PAF acetylhydrolase activity was inversely correlated with the severity of anaphylaxis.

The NEJM study is the first one to report on the roles of PAF and PAF acetylhydrolase in anaphylaxis in humans. It included only 41 patients with anaphylaxis and 23 controls, and its findings need independent confirmation but it looks like PAF and PAF acetylhydrolase will play an important role in diagnosis of anaphylaxis in the future. New medications which block PAF may prevent fatal anaphylaxis.

References:
Platelet-Activating Factor, PAF Acetylhydrolase, and Severe Anaphylaxis. Peter Vadas et al. NEJM, 01/2008.
Rapid Measurement of B-Type Natriuretic Peptide in the Emergency Diagnosis of Heart Failure. Alan S. Maisel et al. NEJM, 2002.
Anaphylaxis Study Offers Clues to Better Diagnosis and Treatment. MedPage Today. Listen to an interview with Peter Vadas, M.D., Ph.D., one of the authors of the NEJM study.