Look for Simpler Hypertension Coding in ICD-10 The rules you'll follow for assigning hypertension codes in ICD-10 will be much the same as the rules you use currently to select the correct ICD-9 hypertension code in M1020/ M1022. Give yourself a refresher in current best practices for coding this condition and you'll be well on your way to mastering the steps for ICD-10 hypertension coding. Primary/Essential Hypertension: 401.xx/I10 To code for primary hypertension in ICD-9, you first need to determine whether the hypertension is malignant, benign, or unspecified. Most hypertension is considered primary or essential hypertension, and in ICD-9, it's coded with a 401.x (Essential hypertension) category code. The fourth digit for 401.x codes indicates whether the hypertension is malignant, benign, or unspecified: In ICD-10, you will no longer need to specify whether primary hypertension is malignant, benign, or unspecified. As a result, the hypertension table, found in the Alphabetic Index in ICD-9, isn't included in ICD-10. All primary hypertension is reported with the same code: I10 (Essential [primary] hypertension).