Pushing Boundaries When Patenting Ranges

by Yifan Mao, MS,* Andrew T. Serafini, PhD,* Glyn Truscott,** and Wenwen Wang, PhD***

Inventions with numerical ranges are valuable across different technologies. Obtaining claims with numerical ranges provide competitive advantages to patent owners. Frequently, a claimed range in an application may need to be narrowed or expanded during prosecution, such as avoiding prior art or capturing an optimized range. Can an applicant add a new range during prosecution? How can an applicant push the boundaries of an existing range in the application to obtain optimal claim coverage? Where do courts and patent offices in different jurisdictions stand when dealing with these issues? What are the strategic considerations when drafting such claims, including numerical ranges? This article addresses these questions.

United States

The United States patent law requires that a patent specification provides a written description in such sufficient detail that a person of skill in the art can reasonably conclude that the inventor had possession of the claimed invention. However, the description need not be in ipsis verbis; rather, the written description requirement is to be applied in the context of the nature of the invention and the state of the knowledge. That is, even if every nuance of a claim is not explicitly described in the specification, the claim is deemed to have met the written description requirement if a skilled artisan would have understood the inventor to be in possession of the claimed invention at the time of filing. Vas-Cath Inc. v. Mahurkar, 935 F.2d 1555, 1563 (Fed. Cir. 1991); Martin v. Johnson, 454 F.2d 746, 751 (C.C.P.A. 1972).

There is no requirement that the exact language corresponding to a numerical range introduced to a claim after filing (hereinafter “the amended numerical range”) must be found in the as-filed application; In some instances, an amended numerical range constructed using a combination of the originally described range and discrete values in the as-filed application can be deemed adequately described. In re Wertheim, 541 F.2d 257 (C.C.P.A. 1976). In In re Wertheim, the as-filed specification discloses a range of 25% to 60% and the specification also discloses a discrete point of 36% as an example.1  The court held the amended numerical range of between 35% and 60% met the written description requirement.  Similarly, In Nalpropion Pharmaceuticals, Inc. v. Actavis Laboratories FL, Inc., 934 F.3d 1344 (Fed. Cir. 2019), cert. denied, 140 S. Ct. 2804 (2020), the court found that an amended numerical range using two discrete values explicitly disclosed in the as filed application as the end values met the written description requirement.2 In Nalpropion Pharmaceuticals, Inc., the claims are directed to a sustained release formulation. The court held that an amended numerical stating a one-hour release rate of “between 39% and 70%” is supported by the specification that discloses one-hour release rates of 39% and 67% separately.3 Similarly, the court held that the claimed range stating a two-hour release rate of “between 62% and 90%” finds support in the specification that discloses two-hour release rates of 62% and 85% separately.4 

Although literal support is not required and discrete data points can be used to combine with as-filed ranges to create new claimed ranges, applicants are not permitted to freely cobble the data points in the as-filed disclosure to create new ranges. A recent case, Indivior UK Ltd. v. Dr. Reddy’s Laboratories S.A.18 F.4th 1323, 1329 (Fed. Cir. 2021), shows that the end values of an amended range must be expressly described in the as-filed application in order to be deemed supported. See our previous discussion of this case here. In Indivior UK Ltd. v. Dr. Reddy’s Laboratories S.A., the Federal Circuit held a claimed range “about 40 wt % to about 60 wt % of a water-soluble polymeric matrix” introduced during prosecution is not supported because neither 40% nor 60% was specifically disclosed in the as-filed specification.5 Notably, about 10 working examples of the composition were disclosed in the specification, the polymer content in each falls within the amended claim range. It is also undisputed that the end values of the claimed range can be readily derived from these working examples using rudimental calculations: by summing the amounts of four types of polymers and dividing the sum by the total amount of the composition (which includes other components in addition to polymers). However, the abundance of working examples and the readily available mathematical tools were not able to cure the deficiency for the lack of the explicit disclosure of the end values. The Indivior court opined “[a] written description . . . requires a statement of an invention, not an invitation to go on a hunting expedition to patch together after the fact a synthetic definition of an invention.”6 The court thus affirmed the Patent Trial and Appeal Board’s decision that the claim lacks adequate written description and held the claim is invalid. 


The written description requirement should be met for claims reciting ranges by explicitly describing the amended numerical ranges or the end values of the amended numerical ranges to show possession thereof as of the application’s filing date. Written description cannot solely rely on cobbling together the numbers of the amended numerical range after the fact, even if only a rudimentary mathematical calculation based on the data in the as-filed disclosure is needed.7  A failure to meet the written description requirement due to the lack of such a statement cannot be cured by disclosing representative working examples within the claimed range. Applicants may need to extract the information from working examples, perform necessary calculations, and show such results and analysis when drafting the application. 


It is well-known that the European Patent Office (“EPO”) takes a relatively strict approach to assessing the basis for amendments in the application as filed under Article 123(2) EPC.8 The same approach is taken when assessing whether “the same invention”9 is described in the priority document to make a valid priority claim.

The “Gold Standard” for assessing the basis for an amended claim at the EPO was confirmed by the Enlarged Board of Appeal in In re Scripps Research Institute, No. G 0002/10 (E.P.O. Aug. 30, 2011), requires that any amended claim must recite what a skilled person would derive directly and unambiguously, using common general knowledge, and seen objectively and relative to the date of filing, from the whole of the application as filed.

Claims to ranges, as were considered by the Federal Circuit in the Indivior UK Ltd. v. Dr. Reddy’s Laboratories S.A. case discussed above, form the basis of a rich vein of EPO case law when considering added matter. In particular, there are plentiful examples of Board of Appeal cases where an application as filed describes parameters and ranges and the claim is amended to subject matter that requires combinations of features from within those ranges or a specific exemplified value. A handful of these cases are discussed below.

Combining Ranges 

When an application as filed discloses both a general and a preferred range, a combination of the preferred disclosed narrower range and one of the part ranges lying within the disclosed overall range on either side of the narrower range is deemed to be derivable from the original disclosure of the patent in suit. For example, in case Showa Aluminum Kabushiki Kaisha v. BEHR GmbH & Co., No. T 925/98 (E.P.O. Mar. 13, 2001), the Board decided that claiming a range from 30-50% found a direct and unambiguous basis in an original disclosure of a general range of 30% to 60% and a preferred range of 35% to 50%. 

However, caution must be applied when considering such amendments because, in Toray Indus., Inc. v. Mitsubishi Polyester Film GmbH, No. T 1170/02 (E.P.O. Mar. 1, 2006), the Board held that combining the lower limit of the general range with the lower limit of the preferred range, thus excluding the preferred range, might not fall under the principles discussed above and could be held to lack basis in the application as filed. In such a case, it is often helpful to consider whether the skilled reader of the patent application would “seriously contemplate” working in the claimed range.10    

It is not usually possible to combine separately disclosed parameters to form a range. In In re DFB Biotech, Inc., No. T 1919/11 (E.P.O. May 15, 2003), the claim at issue recited silver at a concentration of at least 1μM to less than 200 μM. The application as filed stated in two separate consecutive sentences that  “When silver is incorporated in the medium, it will be added at a concentration of less than 900 μM, preferably less than 500 μM, and more preferably less than 200 μM.’ and ‘When silver is incorporated in the medium, it will be added at a concentration of at least 10 nM, preferably 100 nM, more preferably 1 μM, and typically at 10 μM.11  The Board held that this disclosure did not represent an overall range and a preferred range. Combining one of the upper limits mentioned in the first sentence in the description and one of the lower limits mentioned in the second sentence was held not to represent a direct, unambiguous disclosure.

Similarly, in In re Monsanto Technology, LLC, No. T 1320/13 (E.P.O. Jan. 17, 2017), the Board held that a list of individual values such as 1, 2, 3, 4, or 5 does not provide the basis for a claim to “1 to 5.”  This is because a list of individual values—even if disclosed in descending or ascending order—does not relate to values that lie between them. At the same time, a range necessarily encompasses all the values that lie between its two disclosed endpoints, i.e., a list of individual values is conceptually different from a range. 

Forming a range with an isolated value taken from an Example 

An amendment to a feature from an Example is usually only allowed if all elements of the Example are claimed or if the skilled person could have readily recognized that the feature was not so closely associated with the other features of the example as to determine the effect of that embodiment of the invention in a unique manner and to a significant degree.

In Avery Dennison Corp. v. Coloplast A/S, No. T 0876/06 (E.P.O. May 8, 2007), the Board held that the skilled person could have recognized in the application as originally filed that the weight ratio of liquid rubber to solid rubber was not so closely associated with the other features of the examples as to determine the effect of the invention in a unique manner and to a significant degree. Therefore, the value used in several examples could limit the range of the weight ratio of liquid rubber to solid rubber. The limitation of the claim represented merely a quantitative reduction of a range to a value already envisaged within the document and not an arbitrary restriction providing a technical contribution to the subject matter of the claimed invention.

However, again, caution must be applied when considering such an amendment. In T 0517/0712, a newly introduced upper limit had been disclosed in the original application documents only as an isolated value in Example 1. The Board decided that singling out an individual value from a specific embodiment and applying it as a new upper limit in claim 1 created a new- now capped -value range not disclosed in the original documents.


Although the EPO is well-known for its seemingly strict approach to the added matter, the Federal Circuit’s comment in Indivior UK Ltd. v. Dr. Reddy’s Laboratories S.A. that there is no rule “applicable to all description requirement cases involving ranges” is also particularly apt for EP practice.13  As can be seen from the handful of cases discussed above, the facts of a case are always critical when assessing the added matter. 

The principle underlying added matter at the EPO is that the applicant or patent proprietor should not be allowed to improve their position by adding subject matter not disclosed in the application as filed, as this would give rise to an unwarranted advantage and could be damaging to the legal security of third parties relying on the content of the original application. 

When considering the allowability of an amendment at the EPO, features can only be combined if they are direct and unambiguously described in combination in the application as filed. Numerous Board of Appeal decisions reinforce that it is not permissible to treat the application as filed as a reservoir of features that can be fished out and combined later. The combination of features must be described in the application as filed.

Accordingly, a patent application is not a hunting license in the United States, and in Europe, the application is not a reservoir. Applicants should avoid using hunting and fishing analogies to provide complete and unambiguous disclosure of the invention in the application as filed, with increasingly narrower embodiments, e.g., such as narrowing ranges. 


In China, one should follow the Guidelines for Patent Examination to amend one or more numerical ranges in the claims. The Guidelines for Patent Examination issued by the China National Intellectual Property Administration (CNIPA), Part II, Section, Chapter 8, paragraph 5 provides that “Amendment of a numerical range in a technical feature of a claim shall be allowed only when both endpoints of the amended numerical range are described in the original specification and/or claims, and the amended numerical range is within the original numerical range.” 

That is to say, the numerical range intended for amendment should have both endpoints (1) described in the original specification and/or the claims and (2) being within the original numerical range.

Claim a preferred value or range from a continuous numerical range

It is necessary to have two endpoints of a narrower range or the preferred value described in the original application when amending a continuous numerical range (such as a temperature range) into a narrower continuous range or a preferred discrete value. The description may be a direct written description, or it may be determined “directly and unquestionably” through the description of the embodiment.

During the prosecution of Chinese patent application No. 201510259939.4, the examiner rejected amended claim 1 beyond the claim’s original scope (from reciting a formaldehyde trapping agent consisting of two components of 40-60 wt.% each to consisting of 50 wt.% each, based on the specification, which described an example of using 4g for each of the two components).14 The Re-Examination Board found that the value of 50wt.% could be obtained directly and without any doubt based on the example and was within the originally disclosed range, thus accepted this amendment 

Amend an original numerical range consisting of discrete values

To amend a numerical range consisting of discrete values to a specific discrete value, such as amending a battery module containing 3 to 6 cells to a battery module containing 5 cells, those skilled in the art will understand that the number of batteries must be an integer and the range of 3 to 6 cells should be equivalently interpreted as 3, 4, 5, or 6 cells. Therefore, even though the number “5” is not separately described in the original specification, it should be considered part of the original application document.

However, suppose the applicant selectively combines several discrete numerical values described in the original application to form a new continuous numerical range. In contrast, such values have no apparent relationship that could be determined from the application. In that case,  such amendment will be deemed as not directly and unquestionably obtainable from the original application. For example, if the original application describes a temperature condition as 10°C or 300°C but does not disclose the range between these two discrete values being feasible, the amendment from “10°C or 300°C” to “10°C to 300°C” is beyond the description of the original application.

The Chinese patent application No. 201710214051.8 relates to a glipizide orally disintegrating tablet.15 During re-examination, the applicant intended to amend the amount of the purified water used from “30% to 40%” to “26.8% to 40%” of the total weight based on the specification which described not only a general range of 30% to 40%, but also examples disclosing discrete values of 26.8%, 33.4%, 34.1%, 34.3%, 39.5%, and 40%, respectively. The Reexamination Board, however, found that the original specification did not describe a range from 26.8% to 40%, but a discrete value point of 26.8% and a continuous range from 30% to 40% (into which 33.4%, 34.1%, 34.3%, 39.5%, and 40% fell). In contrast, the range of 26.8%-30% could not be directly and unquestionably determined from the original specification and was deemed beyond the original application’s scope.

Excluding values from a numerical range

Sometimes an applicant wishes to distinguish a claim with a numerical range from a cited reference by simply excluding or “abandoning” some values from the numerical range. In contrast, such values are not described directly or unquestionably obtainable in the original specification and claims. Note that an amendment cannot be allowed unless the applicant can prove, based on the original application, that the present invention is impossible to implement when taking such “abandoned” values or that the present invention is novel and inventive when taking the amended numerical range after “abandoning” such values.16 

Numerical ranges for multiple components 

When the applicant amends one or more numerical value (s) or range(s) of a claim with multiple numerical values or multiple numerical ranges, for example, a claim reciting a composition of multiple components with a corresponding content range each, the examiner is also required to understand the overall technical solution of the invention from the perspective of those skilled in the art, determines whether the various numerical values or ranges are closely related with one-to-one correspondence, and decide whether the amendment is beyond the scope of the original application. Suppose the applicant only subjectively selects part of values from a set of closely related numerical values or ranges in the original application to form a new numerical range. At the same time, the specification does not describe the reasons for selecting such values (for example, the selected combination has a better technical effect). It cannot be regarded as “directly and unquestionably” obtained from the original application. 

The Chinese patent application No. 201610687952.4 relates to a liquid crystal composition- comprising compounds of the general formula I-VI. The applicant amended the claimed composition from comprising 5-35% of the formula III compound to 10.5- 26% based on two separate examples (10.5% and 26%). The original examination department objected to this amendment for generalizing from two-point values of 10.5% and 26% to a range of 10.5- 26%, arguing that the components were closely related. Their contents are mutually constrained to form a liquid crystal composition that fulfills the purpose of the invention. However, the Re-Examination Board found that the point values in the examples were within the originally disclosed range of 5-35%. No evidence showed these components and contents were in an inseparable one-to-one correspondence for the invention. The amendment was eventually accepted, revoking the rejection decision.17 


In contrast to the “possession” standard in the US, an amended range is only acceptable if it is literally described in or can be directly and unquestionably determined from the original patent application documents as filed according to the Chinese Patent Law. 

It is worth noting that the “original patent application documents as filed” refer to the patent application documents filed on the filing date, including the claims, the text, and the drawings of the specification. However, it does not include the priority documents. Also noteworthy is that China currently does not accept content incorporated by reference or its use as the basis for the amendment. Therefore, it is highly recommended to include essential contents in the Chinese application in the text directly, instead of incorporation by reference.

Contents that can be directly and unquestionably determined refer to those not explicitly described but can be determined by those skilled in the art based on the as-filed claims, specification, and figures of the original patent application and the common knowledge of the art. From the case studies above, such as CN201510259939.4 and CN201610687952.4, Examiners may take a relatively strict or even rigid standard in determining whether those skilled in the art could determine the basis for amendments from the application. At the same time, the Re-Examination Board could usually provide a more reasonable judgment. 

*Yifan Mao is a senior associate at Kilpatrick Townsend & Stockton, LLP. She can be reached at ymao@kilpatricktownsend.com; 650-324-6311.
*Andrew T. Serafini is a partner at Kilpatrick Townsend & Stockton, LLP. He can be reached at: atserafini@kilpatricktownsend.com; 206 626 7769.
**Glyn Truscott is a partner at Elkington & Fife LLP. He can be reached at: Glyn.Truscott@elkfife.com; +44 20 7936 8817.
***Wenwen Wang is a partner at Advance China IP Law Office. She can be reached at: wangww@aciplaw.com; 86-20-8732 3188 ext. 208 

The opinions expressed are those of the authors and do not necessarily reflect the views of the firm, its clients, or their respective affiliates. This article is for general information purposes and is not intended to be and should not be taken as legal advice.



In re Wertheim, 541 F.2d at 262. 
Id. at 265.
Nalpropion Pharms., 934 F.3d at 1347, 1349 (emphasis added) (quoting U.S. Patent No. 8,916,195 col. 31 ll. 17-18 (filed Dec. 23, 2014). 
Id. (emphasis added) (quoting ‘195 Patent col. 31 ll. 19-20).
Indivior UK Ltd., 18 F.4th at 1325.
Id. at 1329.
Eur. Pat. Off., European Patent Convention, art. 123(2) (July 1, 2020) (“EPC”): “The European patent application or European patent may not be amended in such a way that it contains subject-matter which extends beyond the content of the application as filed.” 
Eur. Pat. Off., European Patent Convention, art. 87(1)(b).
10 T 1170/02 at 4.4.
11 T 1919/11 at 2.2.2 (emphasis added).
12 Available at https://www.epo.org/law-practice/case-law-appeals/recent/t070517du1.html#T_2007_0517 (last visited April 23, 2022). 
13 Indivior UK Ltd., 18 F.4th at 1329-30 (quoting Wertheim, 541 F.2d at 264-65).
14 Re-Examination Decision No. 206957 (CNIPA Mar. 10, 2020).
15 Re-Examination Decision No. 280943 (CNIPA Nov. 1, 2021).
16 Guidelines for Patent Examination §, ch. 8, pt. II.
17 Re-Examination Decision No. 272152 (CNIPA Aug. 2, 2021).
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