Delayed-type allergy to cobalt-comparison of a flow cytometric lymphocyte proliferation test with patch testing.

Background: The patch test is the standard procedure for diagnosing delayed-type sensitization. If a patch test is not possible, the flow cytometric lymphocyte proliferation test (LPT), which determines the number and type of cells responding to a specific antigen in vitro, might be considered as an alternative.
Objectives: Our aim was to establish a flow cytometric LPT for the detection of delayed-type allergic responses to cobalt, and to determine the correlation between stimulation indices (SIs) in LPT and the grade of patch test reactions. With the patch test as a diagnostic reference, we also assessed the sensitivity and specificity of the LPT.
Methods: Fifty-four patients patch tested with the baseline series including cobalt (CoCl ₂ ) were additionally tested with the flow cytometric LPT with CoCl ₂ .
Results: There was a significant correlation between the results of both tests: r _s  = 0.43; P = .001. The LPT with CoCl ₂ showed a sensitivity of 52.6% and a specificity of 85.7%. Corresponding to the low sensitivity of the LPT, high likelihood ratios for a positive patch test reaction were reached only in cases of strong lymphocyte proliferation (SI ≥ 10).
Conclusions: In cases of clearly increased SIs, the flow cytometric LPT with CoCl ₂ gives relevant diagnostic information, and represents a valuable alternative to patch testing.
(© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)