Is there a big difference in the quality of human tissue wax blocks between different companies? How are fixed time and wax block years assessed?

The effects of fixation time and storage duration on peripheral proteins and nuclear antigens cannot be simply generalized. Insufficient fixation can lead to tissue autolysis and antigen diffusion; excessive fixation can cause over-crosslinking, masking antigens and requiring stronger retrieval conditions. Generally, IHC samples fixed in neutral buffered formalin for around 24 hours are relatively reliable, but suppliers may not always have precise records. Regarding storage duration, paraffin blocks stored at room temperature generally maintain acceptable overall stability, but membrane proteins and some phosphorylated epitopes may show more pronounced degradation, while nuclear antigens such as Ki-67 and p53 are relatively robust, though not guaranteed. For batches stored over 5 years or under non-room-temperature conditions, it is recommended to perform small-sample test staining for validation as soon as possible after arrival, rather than directly purchasing in large quantities.

Pre-experimentation must be carried out after arrival, especially if there are no suppliers who have been cooperating for a long time. It is recommended to first use 1-2 white tablets for a mixed antibody/broad spectrum marker verification: if Vimentin looks at the interstitium, CK looks at the epithelium, Ki-67 looks at nuclear proliferation, and then select the target you want to do. In this way, it is possible to judge whether the tissue morphology, fixed state, and antigen repair are in place at the same time. Positive signals should be correctly positioned, the background is not dirty, and the negative and positive areas are clearly defined. If the broad-spectrum markers are not good, there may be a problem with fixation or preservation. Pre-testing can also help you determine the repair method: pH9 antigen repair solution or pH6 classic buffer, different targets need to be tested separately.

It is true that the mass of wax blocks in different companies varies greatly, mainly not in the appearance of the wax blocks themselves, but in the tissue from ex vivo to fixed, fixed liquid type, fixed time, repair blocks and storage conditions. The difference between tens of prices and two or three hundred is sometimes reflected in whether there is a complete fixed record and pathological review. It is recommended to prioritize suppliers that can provide ‘cold ischemia time, fixed fluid type, fixed time, storage life, pathological diagnosis’. Tissue cell morphology integrity and stable antigen expression are more important than inexpensive for IHC-positive controls. You can ask sales to provide QC staining diagrams or white sheets of the same batch of wax blocks first, focusing on whether there is tissue autolysis, nuclear condensation or antigen dispersion, which is more direct than just looking at the certificate.

Don't just focus on unit price when comparing suppliers. It is recommended to make a list: whether the sample source hospital/sample library, ethical approval, pathological review are completed by the pathologist, whether HE biopsies are provided, whether QC white tablets are provided, fixed records, retention period, whether a small trial purchase is supported, and whether the return and replacement are accepted if the staining results are not satisfactory after sales. For normal tissue positive control, I pay more attention to whether the tissue type is accurate and whether the normal structure is complete, rather than just the price. Two or three white tablets of the same type can be stained in parallel in the same batch of IHCs, and scored with signal strength and positioning consistency. In this way, the batch risk will be much smaller if it is purchased in bulk later.