Formalin has a number of uses such as tissue fixative, embalming agent, disinfectant and biocide. It is toxic to living tissues and can cross-link proteins.
Impact depends on:
(1) concentration of formaldehyde
(2) duration of exposure
(3) concurrent exposures (heat, cold, chemicals)
(4) handling after exposure (washing, pretreatment, etc)
False negative test results can occur with:
(1) microbiological culture (bacterial,fungal, etc)
(2) cell culture (cytogenetics, other)
(3) enzyme tests (urease for Helicobacter, other)
(4) antigen detection tests (if target site becomes altered)
(5) some molecular tests (if specimen not pretreated)
A specimen with a very brief exposure to a dilute formalin solution and that is rapidly rinsed may give a valid result but is at risk for contamination and reduced sensitivity.
Responses to situation:
(1) resampling
(2) use of an alternative method of analysis that is not interfered with by the formalin exposure
