lady questioning who can memorize 72,184 diagnosis codes

Did you know there is a way to master ICD-10-CM codes by the chapter letters? Obviously, there is no way to remember all of the codes in ICD-10-CM, especially since there are 72,616 of them.

There is a strategy, however, that 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 2021)

The ICD-10-CM coding updates for fiscal year 2021 took effect on October 1, 2020, and are valid until September 30, 2021, according to the Centers for Medicare & Medicaid Services (CMS).

The updates included 490 new codes, 47 revised codes, and 58 deleted codes. Most of these code changes came from the following chapters:

New Codes

  • Chapters 3: Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (D50-D89) – 43 new codes
  • Chapter 13: Diseases of the musculoskeletal system and connective tissue (M00-M99) – 57 new codes
  • Chapter 19: Injury, poisoning and certain other consequences of external causes (S00-T88) – 128 new codes
  • Chapter 20: External causes of morbidity (V00-Y99) – 125 new codes

Revised Codes

Chapter 21: Factors influencing health status and contact with health services (Z00-Z99) – 39 revised codes

Deleted Codes

Chapter 19: Injury, poisoning and certain other consequences of external causes (S00-T88) – 23 deleted codes. 

Other code updates took effect in other chapters but on a smaller scale.


Although it is impossible for a medical coder to memorize all the ICD-10-CM codes, there is a way to get you close. That’s what Laurie Johnson states, and I agree. 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 currently 22 chapters in ICD-10-CM for FY 2021, with the letter “U” being added. The codes range from A00 to Z99 and are described below. 

list of 22 chapters of ICD-10-CM, their chapter titles and code ranges

22 Chapters in ICD-10-CM for FY 2021, with the letter “U” being added.


Chapter 22: Codes for special purposes (U00-U85) only has two codes so far, which are listed under a new section called “Provisional assignment of new diseases of uncertain etiology or emergency use” (U00-U49). One code is for vaping-related disorder (U07.0), and the other code is for COVID-19 (U07.1). These codes actually went into effect the first part of the year.  

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 2 and 3 (D) and 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.

How mnemonics make it easier to master icd-10-cm codes by the chapter letters

But that’s not all! After you have reviewed this information and downloaded the chapter cheat sheet, be sure and take the quiz to find out if you are a true ICD-10-CM Medical Coding Expert! Then get the detailed handout with answers and rationales.