Version July 2025
| Test | Comment |
| Total tryptase (serum/plasma) | Mature + proforms of alpha/beta tryptases. Maximal elevation above baseline 30 to 120 minutes after onset of anaphylaxis, reflecting release of mature tryptase(s). Declines to baseline with a half-life of approximately 2 hours. Comparing acute and baseline levels improves sensitivity and specificity. |
| Histamine (plasma) | Peaks 5 to 10 minutes after symptom onset and declines to baseline by 15 to 30 minutes. Histamine may be released ex vivo by disrupting basophils in blood when passed through a small-bore needle under vacuum or when blood clots. |
| N-methylhistamine (24-hour or spot acute urine) | Normalized to creatinine concentration. May be elevated in urine collected up to 24 hours after symptom onset, but histamine-containing foods and histamine-producing mucosal bacteria may be problematic sources. |
| 11-beta-prostaglandin F2-alpha (24-hour or spot acute urine) | Normalized to creatinine. Prostaglandin D2 metabolite; falsely low if cyclooxygenase inhibitor taken; produced by activated mast cells, eosinophils, antigen-presenting cells, megakaryocytes, and T helper type 2 lymphocytes but not by basophils. |
| Leukotriene E4 (24-hour urine) | Leukotriene C4 metabolite; produced by mast cells, basophils, eosinophils, certain phagocytic mononuclear cells, endothelial cells, vascular smooth muscle cells, and platelets. |
