What is immunohistochemistry (IHC)?
A. Immunohistochemistry is a laboratory diagnostic procedure that uses antibodies to detect target antigens in formalin-fixed paraffin-embedded tissue sections, following routine histologic examination. These antigens may be tissue dependent, represent proliferative cell markers or be associated with specific infectious agents.
In what circumstances is immunohistochemistry recommended?
IHC is a diagnostic aid and is not appropriate in all situations. Your pathologist will generally advise when it may be useful and interpretation always needs to take into account the original histopathology findings. The following are some common circumstances in which IHC is used:
- The distribution of some antigens is tissue dependent, and IHC can be used to investigate the cell lineage and hence deduce the origin of some poorly-differentiated neoplasms.
- IHC can be used to identify certain infectious agents in tissue sections (e.g. Feline coronavirus, Toxoplasma).
- Certain antibodies can be targeted in some tumours to help provide prognostic information (e.g. T/ B cell lymphoma phenotyping and proliferation antibody ki67 in some mast cell tumours and melanocytic tumours).
- A decision to proceed with IHC always needs to take into account the clinical circumstances for each case; i.e. you should always ask yourself whether advancing the diagnosis will be likely to alter the prognosis and/or treatment.
Does IHC always provide a definitive diagnosis?
The outcomes of IHC vary with the reasons for performing the tests. In many cases IHC can provide a definitive diagnosis. In some circumstances IHC may be used to exclude certain diagnoses, whilst in other cases it may simply attempt to better characterise a neoplasm or identify an organism.
Some things that may limit the IHC diagnosis:
- The availability of antibodies (not all antibodies reported in the literature are available in the routine diagnostic setting).
- Small amount of diagnostic tissue available (very small biopsy size or tumours in which there is extensive necrosis).
- Some neoplasms (e.g. intestinal lymphoma) may have mixed populations of cells or a background of inflammatory cells that may complicate interpretation.
- Very poorly differentiated neoplasms may exhibit abnormal antigen expression or lack specific antigen expression.
- In circumstances where a definitive diagnosis cannot be made, your pathologist will provide you with the most likely differentials or may suggest other tests to further investigate (e.g. PARR for lymphoma).
How long does it take?
This depends on the antibody. Laboratories typically stock a range of commonly used antibodies and, in the vast majority of cases, you will receive the results from these within 5 -7 business days after the request is made.
Less common and more specialised antibodies (including most infectious agents) may need to be performed at specific external referral laboratories (some are overseas) and this may add to the turn-around time. Your laboratory will be able to advise you on estimated turn-around times in these instances.
Do I need to submit new tissue?
No, you will not typically need to submit new tissue. We use the tissue that we have already processed for routine histopathology. In this way we can ensure that the most appropriate tissues/sections are used.
Rarely, the biopsy fragments will be too small for IHC studies and the pathologist may need to request more tissue samples from you.
Can I perform IHC without doing routine histopathology first?
No, tissues need to be processed for routine pathology in order to perform IHC. Initial evaluation of the H+E sections also permits the pathologist to select the best tissue sections for IHC. Furthermore, it is critical that IHC is always interpreted in conjunction with morphologic features that are best assessed on routine H+E stains.
How much does it cost?
This depends on the type of type and number of antibodies. When differentiating between tumour types, panels of antibodies are generally more often diagnostic than single antibodies. Your pathologist will attempt to use antibodies in the most efficient manner balancing diagnostic value against cost. Depending on the results of the initial antibody panel, supplementary antibodies/panels may be suggested to further characterise the lesion. Certain antibodies and panels have fixed prices (see price list). However, in many circumstances, the antibody panels are customised to the individual lesion and patient. As such, prices will vary and your pathologist will be able to provide a quote.
If you are unsure of whether IHC is worthwhile, please always feel free to call/email the reporting pathologist who can advise with regard to tissue viability/availability, and the most judicious use of IHC markers to achieve your diagnostic goals.
For more information, contact your Vetnostics Pathology laboratory.
