There are five primary ways in which a patent can be corrected or affected after it has been issued, wherein the proceedings are handled by the Central Reexamination Unit (CRU), although the first two that will be discussed do not actually involve a reexamination of the patent in question (despite the name Central Reexamination Unit). These five ways of correcting or affecting a patent are: statutory disclaimers, certificates of correction, reissue, ex parte reexamination, and supplemental examination. Other ways of affecting a patent after issue include trial proceedings that are conducted by the Patent Trial and Appeal Board, and include inter partes review, post grant review, and covered business method review. If a patent owner is aware of any issue or error in their patent, they must choose the correct route for addressing those issues or errors.

Before the formation of the CRU, requests for reexamination would be routed back to the art unit that originally worked on that patent. These requests were uncommon when compared to the typical examination work that examiners performed in their day-to-day work, and thus, the examiners were not always familiar with reexamination proceedings. When the CRU was formed in 2005, the centralization of these types of requests allowed experienced examiners dedicated to the reexamination of patents to become specialized in these matters. Another advantage of the CRU is that it helped to eliminate some of the bias that might be present when a reexamination request went back to the art unit that issued a patent, since the older system might have caused a reluctance to admit the art unit had issued an erroneous patent.

Statutory disclaimer

The statute, in 37 CFR 1.321, allows a patent owner to disclaim any complete claim or claims, or patent. There are a few reasons why an owner might want to do so, and an example is to reduce issues during court proceedings. A fee is required for a statutory disclaimer.

More information about statutory disclaimers can be found in MPEP chapter 1490.

Certificate of correction

Minor errors in a patent can be fixed by filing a certificate of correction. The CRU reviews the error, and if the error was the fault of the USPTO, there will be no associated fee. Errors made by the applicant must be corrected with a fee.

The types of errors that the certificate of correction is used for is limited and include only minor errors such as typos or spelling mistakes, and as such, the terms of a claim cannot be corrected by using a certificate of correction.

More information about certificates of correction can be found in MPEP chapter 1481.


A reissue is used for making more substantive changes or corrections than a certificate of correction is used for. It is an option that is only available to patent owners, and it requires a fee. For a reissue to take place, the errors that are to be corrected must be errors that would render the patent wholly or partly inoperative, or invalid. If the patent was assigned, it is required to file a consent of the owner for the reissue.

During a reissue, additional dependent or narrower claims can be added. However, there is a limitation to adding broadening claims. A broadening reissue must be filed within two years from the grant of the original patent. If an amended claim is broader in any respect than the original claim – even if it was narrowed in other respects – the claim has been broadened. To understand how “broadening” is defined, an “infringement test” can be used, which is: if someone infringes on the amended claim, but was not previously infringing on the original claim, then the claim has been broadened.

Since the reissue is only for the unexpired portion of a patent’s term, if a patent were to expire during the course of a reissue prosecution, the proceedings are terminated. This is not the same for reexamination, which could affect the entire period of enforceability of a patent.

More information on reissues can be found in MPEP chapters 1410, 1410.01, and 1411.

Ex Parte Reexamination

            Under the reexamination statute 35 U.S.C. 302, “Any person at any time may file a request for reexamination by the Office of any claim of a patent on the basis of any prior art cited.” This means that the patent owner or a third party (who receives copies of all communications from the Office during the reexamination proceeding) can file the request, and the requester can remain anonymous. The reexamination can be requested for one or more claims, and the general practice of the CRU is to examine only those claims that were requested. This reexamination will be on the basis of prior art only, meaning that other issues, such as 35 U.S.C. 112 issues, cannot be addressed.

            The process begins with the filed request, which, if it was proper, is given a filing date. A proper request must be in writing, accompanied by a fee, and must be based only on printed publications or patents – it cannot be based on, for example, an affidavit or other such evidence. These can be used, but not as the basis, and can only be used to support the prior art that the reexamination is based upon.

The threshold for initiating the reexamination proceeding after the request is filed is called a “substantial new question of patentability” (SNQ). A determination of whether or not SNQ has been raised must be made by the Office within three months. If the examiner determines that an SNQ is raised, then the examiner will order the reexamination; otherwise, the request is denied. A patent owner can have the opportunity to make a statement (or waive the right to do so), and a third party filer may comment on that statement. Afterwards, the third party will have no role in the reexamination proceeding. Then, the reexamination is conducted much like the examination process of a patent application, with a few exceptions. For one, no Request for Continued Examination is offered – there is only one opportunity to amend as a matter of right. Another difference during the examination process is that the reexamination uses “special dispatch,” which means that extensions of time are not automatic and are only granted with cause, and times for reply can be shortened (particularly the case when the patent is involved in a court proceeding). Another important difference is that amendments cannot be broadening during a reexamination. The proceeding concludes with a certificate of reexamination.

            More information on ex parte reexamination can be found in MPEP chapter 2209.

Supplemental Examination

            Supplemental examination came about with the America Invents Act (AIA), and can only be filed by the patent owner. A primary difference between supplemental examination and an ex parte reexamination requested by the patent owner is that in an ex parte reexamination, only prior art issues can be raised; in supplemental examination, all issues can be raised, including issues related to subject matter eligibility of 35 U.S.C. 101 or written description requirements of 35 U.S.C. 112. The patent owner can request that the Office “consider, reconsider, or correct information believed to be relevant to the patent,” according to the statute, 35 U.S.C. 257.

            There are two phases of supplemental examination. The first is the supplemental examination phase, and a second reexamination phase that could result from the findings of the first phase. The reexamination generally proceeds similarly to the reexamination of the ex parte reexamination discussed above, with a few exceptions. Notably, the reexamination is not limited to prior art issues.

            The supplemental examination does not involve any interaction between the requester and the Office, and concludes with a certificate to indicate whether or not the “items of information” provided by the patent owner (which are limited to twelve) raised an SNQ. Like in ex parte reexamination, the Office must make this determination within three months.

            A primary advantage of supplemental examination for a patent owner is that it provides the owner with a potential mechanism for immunizing themselves against allegations of inequitable conduct. That is, when information is considered, reconsidered, or corrected during this process, the patent cannot be “held unenforceable on the basis of conduct relating” to this information (35 U.S.C. 257(c)(1)). Thus, it can be advantageous for a patent owner in some situations to request a supplemental examination, particularly over an ex parte reexamination if items of information are available which are not based on printed publications or patents.

            More information about supplemental examination can be found in MPEP chapter 2802.


The USPTO website for the CRU can be found at:


Disclaimer: The views and opinions expressed throughout this blog are the views and opinions of the individual author(s) and/or contributor(s) and do not necessarily reflect the views and opinions of our firm, CIONCA IP Law. P.C.

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Marin Cionca, Esq.

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USPTO Reg. No. 63899



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