Revisiting serum storage protocols: assessing the impact of temperature variations on indirect immunofluorescence testing for pemphigus and bullous pemphigoid.

Background: Indirect immunofluorescence (IIF) plays a crucial role in the diagnosis of pemphigus and bullous pemphigoid (BP) by detecting the presence of circulating autoantibodies in the serum of patients. The standard serum transportation method requires delivery to laboratories at 2-8 °C within a day and storage at -20 to -80 °C. However, this protocol poses logistical challenges.

Objectives: To carry out a study assessing how temperature variations affect the accuracy of IIF tests.

Methods: This case-control study analysed 203 serum specimens: 102 from patients with pemphigus and 101 from patients with BP. Specimens were stored at -80 °C (control), 24 °C and 40 °C for 7 days before analysis to investigate variations in IIF titres between test and control conditions.

Results: In pemphigus serum, 95% of specimens at 24 °C and 76% at 40 °C showed no titre difference compared with controls. Similarly, 89% of BP serum specimens at 24 °C and 82% at 40 °C matched the control titres. While 57 specimens across both groups experienced reduced titres, the decrease was primarily marginal (a 1-step reduction in 54 cases, 2-step in 3), with no transition from positive to negative results.

Conclusions: Storing serum at 24-40 °C for up to 7 days before testing only slightly influences IIF outcomes for pemphigus and BP. These findings could prompt a significant revision in the existing strict transport guidelines, ensuring efficient use of resources without sacrificing the accuracy of diagnostic tests.