lady questioning who can memorize 72,184 diagnosis codes

There are way too many ICD-10-CM codes to remember them all. In fact, there are 72,184 codes to be exact. But did you know there is a strategy you can use that will get you into the right ballpark, so to speak?

In this post, I’ll explain how to master ICD-10-CM codes by the chapter letters. I’ll also provide you with a fantastic cheat sheet for quick reference. You will love it!

ICD-10-CM Codes (FY 2020)

The ICD-10-CM coding updates for fiscal year 2020 took effect on October 1, 2019, and are valid until September 30, 2020, according to the Centers for Medicare & Medicaid Services (CMS).

According to the American Health Information Management Association (AHIMA), we have 273 new codes, 21 deleted codes, and 30 code title revisions since fiscal year 2019.

Most of the changes took place in Chapters 9, 12, 17, 19, and 20, and most of them are new codes to enhance data specificity.

Other chapters that show minor changes and/or deletions include Chapters 1, 3, 6, 7, 10, 13, 14, 18, and 21.


Although it is impossible for a medical coder to memorize all the ICD-10-CM codes, there is a way to get you into the right chapter. It’s called mnemonics. Mnemonics is a strategy used to help improve your memory and learn important information.

Let me explain:

In ICD-10-CM, the first digit of each code is an alpha character. By using mnemonics, you can connect the first letter of a diagnosis code with the corresponding ICD-10-CM chapter. This will not only make it easier for you to find the first letter of the ICD-10-CM code, but it will also make it quicker.

And time is critical when you are taking a medical coding exam!

That’s why I have created an ICD-10-CM Chapter Cheat Sheet.

Chapters in ICD-10-CM

There are 21 chapters listed in ICD-10-CM. The codes range from A00 to Z99 and are described below. The letter “U” is not used.

list of 21 chapters of ICD-10-CM, their chapter titles and code rangesges based on

Some things to note as it relates to the codes in ICD-10-CM:

  • Each code starts with a letter.
  • Each letter is associated with a specific chapter in ICD-10-CM.
  • Some chapters have more than one letter, such as Chapters 1 (A, B), 2 (C, D), 19 (S, T), and 20 (V, W, X, Y).
  • Some chapters share beginning letters, such as Chapters 7 and 8 (H).

Once you learn the associated mnemonic for each chapter, you will be able to determine the appropriate chapter for a given code.

The mnemonic for each chapter is listed on the ICD-10-CM Chapter Cheat Sheet I am providing through the signup form.

For additional information about the specific types of codes that can be found in each chapter, refer to your current ICD-10-CM coding manual.


Here are some examples to help you better understand how mnemonics will help you determine the first letter and chapter for each code.

Example #1

The mnemonic for Chapter 9, Diseases of the circulatory system (I00-I99), is “Infarction.” Think myocardial infarction or heart attack. This relates to the circulatory system. Therefore, a code related to the circulatory system begins with the letter “I.”

Taken from a different angle, if we see code I10, we immediately know that this code relates to the circulatory system. How do we know this? We know this based on the first letter “I.” And if we look up I10 in the ICD-10-CM coding manual, I10 refers to Essential (primary) hypertension. Hypertension is high blood pressure and it relates to the heart, or circulatory system (Chapter 9).

Example #2

The mnemonic for Chapter 4, Endocrine, nutritional and metabolic diseases (E00-E89), is “Endocrine.” If we see an exam question with E11.65 as one of the possible answers, we can see from the first letter “E” that it relates to the endocrine system. When looking up E11.65, it takes us to Type 2 diabetes mellitus with hyperglycemia.

Type 2 diabetes mellitus is a disorder of the endocrine system, and hyperglycemia is a complication of diabetes. Therefore, it makes sense that the first letter is “E“.

Example #3

A patient is diagnosed with major depressive disorder, recurrent, mild.

If I know my mnemonics, even before I look up the code for this diagnosis, I know that the first letter of the code is an “F“. The reason I know this is because the mnemonic for Chapter 5, Mental, behavioral, and neurodevelopmental disorders (F01-F99), is “Feelings of hopelessness.” The first letter is “F,” and depression codes are located in Chapter 5.

I can verify this by looking up the code in the Alphabetic Index under disorder, depressive, major, recurrent, F33 Major depressive disorder, recurrent. In the Tabular, F33.0 can be verified as Major depressive disorder, recurrent, mild.

Hopefully, now you get the idea as to how mnemonics work for mastering ICD-10-CM codes by the chapter letters.

And once you have the ICD-10-CM Chapter Cheat Sheet with all of the mnemonics listed, it should be even more clear and make things much easier.

So download the free cheat sheet and please comment below to let me know if it’s been helpful. If you find it helpful — and I believe you will — please be sure to share this link with others who may be interested.

Or share the image below on Pinterest so others can learn from it as well.

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