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How to Search

National Guideline Clearinghouse™ (NGC) provides you with three options for searching:

Basic Search

Detailed Search

Frequent Searches

Search Tips

Words entered this way:

Will be searched in a way that:

Diabetes Finds the word diabetes -- No variations
diabet* Finds the word diabetes, diabetic, and other word ending variations
"heart failure" Finds the exact phrase heart failure
diabetes AND pregnancy Finds the words diabetes and pregnancy anywhere in the guideline summary
colon OR colorectal Finds the word colon or the word colorectal, but not necessarily both

Boolean Operators

The NGC Search and Detailed search options support the use of the Boolean operators grouping characters and wildcard/truncation symbols


The Boolean operator "AND" narrows a search, retrieving only those guidelines containing at least one term from each concept. The AND operator is very good for narrowing a search to retrieve those guidelines most relevant to your topic.


The Boolean operator OR broadens a search, retrieving all guidelines containing at least one of the search concepts entered, but not necessarily both. The OR operator is very good for linking synonyms or related concepts in order to retrieve as many relevant guidelines as possible.


You can also use parentheses to construct your search strategies.

For example: entering the search expression -- (hip or knee) and arthroplasty -- will retrieve those guidelines containing the terms hip and arthroplasty or the terms knee and arthroplasty


You can find plural forms of words or word-stems using the '*'. Asterisks can be placed at the start of a term or at the end or a term.


The use of double quotation marks around your search phrase (e.g., "prostate cancer screening") is recommended if you would like to narrow your search to find summaries that contain the specific phrase. This search is more likely to retrieve content specifically related to your search expression.


The use of double quotation marks is required for complex searches that include multiple phrases and/or Boolean operators, parenthetical grouping, or wildcard/truncation characters. For instance, when your search query contains an operator, you must enclose any multi-word phrase in double-quotation marks. Take for example the following search expression:

Aspirin AND "Cardiovascular Disease" AND (Mortality OR "Death*")

Note the use of double quotation marks around the phrase "Cardiovascular disease" and around the wildcard/truncation for "Death*"

Automatic Concept Mapping

As appropriate, the NGC search engine attempts to map (match) the specified search terms/phrases against a standard table of disease/condition and treatment/intervention concepts derived from the U.S. National Library of Medicine's (NLM) Unified Medical Language System (UMLS)

If a match is found in the table, the NGC then searches for these terms in the Disease/Condition and/or Treatment/Intervention fields in the database.

If a match is not found in the table, the NGC searches the terms/phrases as a text word(s).

Here are some examples of how the concept mapping works:

Textword Searches

In addition to concept mapping, NGC will attempt to find the terms or phrases specified in your search query within the text of the NGC summary. If you are looking for a guideline related to a specific phrase, we recommend that you enclose your phrase in quotes.

Running your Search

Once you have entered your search criteria, click on the "Search" button to run the search.

search button image

The results will appear on your screen.

Sorting and Displaying Search Results

NGC will automatically return your search results sorted by relevance, with the most relevant guidelines listed first. This is derived through the use of a term-weighting algorithm.

An alternative option for sorting your search results by publication date is available through the Detailed Search.

From the search results page, you can either:

Frequently Asked Questions - Searching

Is NGC searching the complete, full-text guideline for my search terms?

No. In the Basic Search mode, NGC searches the contents of the complete Guideline Summary Sheet for any guideline. In the Detailed Search mode, NGC searches the specific field in the database corresponding to the criteria you enter or select. This is done to improve the relevance (precision) of the search results.

Is the NGC search engine case sensitive?

No, NGC searches do not recognize the difference between upper and lower case letters.

My search returned a results page stating "no guidelines were found" -- Why doesn't NGC have any guidelines on my topic?

Sometimes when searching, I hit the "Back" button of my browser and get a "Page Cannot be Displayed" error message. Is there something I can do to prevent this error?