Tick Bites

Image of an engorged tick on person's arm
An engorged tick on a person’s arm

The Coding Challenge


A 23-year-old male presents with an engorged tick on his left arm. He has no medical or surgical history and currently shows no symptoms. On examination, a small unidentifiable tick is seen on his left upper arm. There is no sign of a rash. The patient is given a single dose of doxycycline. Assign for ICD-10-CM.

A. W57.XXXA, S40.872A
B. S41.152A, W57.XXXS
C. W57.XXXS, S40.862S
D. S41.152A, W57.XXXA


D. S41.152A, W57.XXXA

A tick is a nonvenomous arthropod. When a tick bites an animal or human, it is considered an open bite because they use their teeth to cut or tear the skin and surrounding tissue.

Locate and Verify

To locate tick bite in the Alphabetic Index of the ICD-10-CM coding manual, go to Bite (s) (animal) (human)/arm (upper) S41.15-.

In the Tabular List, Open bite of left upper arm is reported with S41.152. However, S41.152 is not a valid code. It requires a 7th character to specify the episode of care (“A” for initial encounter, “D” for subsequent encounter, or “S” for sequela). Since the patient is receiving active treatment, we need to add “A” to the code, making it:

S41.152A, Open bite of left upper arm, initial encounter

There is also a note that indicates we need secondary code(s) from Chapter 20 to indicate the cause of injury. The cause was a bite from a tick.

According to the ICD-10-CM Official Guidelines for Coding and Reporting, most categories in chapter 19 have a 7th character requirement.

  • 7th character “A” initial encounter is used for each encounter where the patient is receiving active treatment for the condition.
  • 7th character “D” subsequent encounter is used for encounters after the patient has completed active treatment of the condition and is receiving routine care for the condition during the healing or recovery phase.
  • 7th character “S” sequela is for use for complications or conditions that arise as a direct result of a condition, such as scar formation after a burn. The scars are sequelae of the burn.

The coding guidelines also state that external cause codes cannot be a principal (first-listed) diagnosis. Consequently, the “S” code for the bite and its location should be sequenced first.

To locate the external cause code, we need to go to the External Causes of Morbidity codes in Chapter 20. Look under Bite, bitten by/arthropod (nonvenomous) NEC W57. W57, Bitten or stung by nonvenomous insect and other nonvenomous arthropods, is not a valid code. It requires a 7th character to indicate the episode of care. Here again, the patient is receiving active treatment, so “A” needs to be added to W57. Placeholder “X” is needed in the fourth, fifth, and sixth character positions. We can verify our correct code as:

W57.XXXA, Bitten or stung by nonvenomous insect and other nonvenomous arthropods, initial encounter

Before making your final code selections, be sure to review all the instructional notes provided such as Includes, Excludes1, Excludes2, and Code Also.

Incorrect Answers

A, B, and C are incorrect.

A. W57.XXXA, S40.872A. W57.XXXA is the correct code but is sequenced incorrectly. S40.872A refers to Other superficial bite of left upper arm.

B. S41.152A, W57.XXXS. W57.XXXS refers to Bitten or stung by nonvenomous insect and other nonvenomous arthropods, sequela.

C. W57.XXXS, S40.862S. Again, W57.XXXS is the wrong code. S40.862S refers to Insect bite (nonvenomous) of left upper arm, sequela. In addition, the S code must be sequenced first, followed by the external cause code.

How’d you do? 

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** This post has been updated to reflect FY 2022 ICD-10-CM Coding Guidelines. **


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