ICD-10 Code for Blood Blister

If you have ever discovered a dark, raised bump on your skin after getting your finger pinched in a door or wearing ill-fitting shoes, you have likely encountered a blood blister.

While most blood blisters heal on their own, sometimes you need to see a doctor. And when that happens, a medical coder must assign the correct ICD-10 code for your medical record and insurance claim.

So, what is the right code?

Let’s be clear from the start. There is no single ICD-10 code labeled exclusively “blood blister.” Instead, you must choose a code based on the blister’s location, cause, and whether it has complications like infection.

This article will walk you through everything you need to know. We will cover the main codes, how to use them correctly, and common mistakes to avoid. By the end, you will feel confident finding the right code for any blood blister scenario.

What Exactly Is a Blood Blister? (A Quick Refresher)

Before we dive into coding, let’s understand what a blood blister is. This helps you choose the correct code.

A blood blister is a type of blister that forms when small blood vessels (capillaries) near the skin’s surface break open. The injury is usually caused by a pinching, crushing, or shearing force. The leaked blood pools inside a pocket between the skin layers, creating a raised bump that appears red, purple, or almost black.

Key differences from a regular blister:

• Regular blister: Filled with clear fluid (serum).

• Blood blister: Filled with blood or a mix of blood and clear fluid.

Common causes:

• Closing a door on your finger

• Wearing tight shoes that rub repeatedly

• Using tools like pliers or hammers without gloves

• Getting your skin caught in a zipper

Note to readers: Most blood blisters are harmless and resolve within one to two weeks. Never try to “pop” a blood blister at home. This can introduce bacteria and lead to a serious infection. If a blister is painful, large, or in an unusual location, let a healthcare professional handle it.

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The Primary ICD-10 Code for a Blood Blister

Now for the answer you came here to find.

In the ICD-10-CM (Clinical Modification) system, the most commonly used code for a simple, uncomplicated blood blister is:

S90.9 – Unspecified superficial injury of lower leg, ankle, foot, and toes

Wait – that seems specific to the foot. What about fingers?

Let me explain. Many coders use codes from category S60 (Superficial injury of wrist, hand, and fingers) for blood blisters on the hands. For example:

• S60.429 – Blister (nonthermal) of unspecified finger – This is frequently the correct choice for a blood blister on a finger when the cause is mechanical (pinch or rub).

So, which code is truly correct?

The honest answer: You must code based on the anatomical location and the type of blister.

Here is a simple rule:

In clinical practice: Most dermatologists and general practitioners document a simple blood blister as a “nonthermal blister.” The “nonthermal” distinction is critical. It tells the insurance company the blister was not caused by a burn or fire.

Important note: Do not use burn codes (T20–T32) for a blood blister. A blood blister is a mechanical or friction injury, not a thermal burn. Using the wrong code can lead to claim denials.

Detailed Coding by Body Region

Let’s break this down by where the blood blister appears. This is the most practical way to code correctly.

H2: Blood Blister on Finger or Hand

This is the most common location. Think of a child with a pinched fingertip or a mechanic with a blood blister from a wrench.

Primary code: S60.429 – Blister (nonthermal) of unspecified finger.

More specific options:

• S60.421 – Blister (nonthermal) of right index finger

• S60.422 – Blister (nonthermal) of left index finger

• S60.429A – Initial encounter (first time seeing the doctor)

• S60.429D – Subsequent encounter (follow-up visit)

Documentation tip for doctors: Always specify which finger and which hand. For example: “3 mm blood blister on the distal pad of the right middle finger due to pinch injury from a car door.”

H2: Blood Blister on Foot or Toe

Second most common location. Runners, hikers, and anyone wearing new shoes often get these.

Primary code: S90.919 – Blister (nonthermal), unspecified foot.

More specific options:

• S90.911 – Blister (nonthermal) of right great toe

• S90.912 – Blister (nonthermal) of left great toe

• S90.914 – Blister (nonthermal) of right lesser toe(s)

• S90.915 – Blister (nonthermal) of left lesser toe(s)

Important: If the blood blister is caused by a known foreign object (like a pebble in the shoe), you may also need an external cause code from Chapter 20 (e.g., W45.8 – Other foreign body entering through skin). But for simple friction from shoes, no external cause code is required.

H2: Blood Blister on Arm, Leg, or Trunk

These are less common but still occur. Think of a blood blister from a blood pressure cuff that was too tight or from a seatbelt during a minor car accident.

Primary code for arm: S50.929 – Blister (nonthermal) of unspecified part of forearm.

Primary code for leg: S80.929 – Blister (nonthermal) of unspecified part of lower leg.

For the trunk (chest, back, abdomen): Use S30.92X – Blister (nonthermal) of unspecified part of abdomen, lower back, or pelvis.

H2: Blood Blister Inside the Mouth (Oral Blood Blister)

This is a special case. Oral blood blisters are often called “angina bullosa hemorrhagica.” They look scary but are usually harmless.

ICD-10 code for oral blood blister: K13.79 – Other lesions of oral mucosa.

Alternate code: K11.6 – Mucocele of salivary gland (if the blister is on the lower lip and looks like a mucus-filled cyst with blood).

Reader note: If you see a blood blister inside your mouth that keeps coming back in the same spot, tell your dentist or doctor. Very rarely, it can be a sign of a bleeding disorder or a vascular lesion.

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When the Blood Blister Is Not Simple: Complications & Secondary Codes

Not every blood blister stays simple. Sometimes things go wrong. Here is how to code those situations.

H2: Infected Blood Blister

If a patient tries to pop the blister at home, bacteria can enter. Signs include increasing redness, warmth, pus, or red streaks going up the arm or leg.

Primary code for the blister itself: Same as above (S60.429, S90.919, etc.)

Add a secondary code for the infection:

• L08.9 – Local infection of skin and subcutaneous tissue, unspecified

• L03.031 – Cellulitis of right hand (if severe)

• L03.119 – Cellulitis of unspecified part of foot

Example: A patient has an infected blood blister on the left index finger from trying to drain it with a needle.

• Code 1: S60.422 – Blister (nonthermal) of left index finger

• Code 2: L08.9 – Local infection of skin

H2: Ruptured or Bleeding Blood Blister

If the blister breaks open on its own and is now an open wound:

Change the code to an open wound code:

• S61.229 – Laceration without foreign body of unspecified finger (if the skin is torn open)

• S91.109 – Unspecified open wound of unspecified foot

Do not keep the blister code after it ruptures. The blister no longer exists as a closed structure.

H2: Recurrent Blood Blisters (Without Known Cause)

Some people get blood blisters over and over again, often on their hands or feet, with no clear injury. This can be a sign of a skin fragility disorder or a vascular problem.

In this case, the blister is a symptom of an underlying condition.

Possible codes:

• Q81.8 – Other epidermolysis bullosa (a genetic condition causing fragile skin)

• D69.2 – Other nonthrombocytopenic purpura (bleeding into the skin)

• L98.9 – Disorder of skin and subcutaneous tissue, unspecified

Important disclaimer: Do not assume a recurrent blood blister is a genetic disorder. Most recurrent blood blisters are still caused by minor repeated trauma (like playing guitar or using crutches). Document the cause clearly.

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Coding for Different Patient Scenarios (Real-World Examples)

Let’s walk through four common clinical scenarios. This will help you see how the codes work in practice.

Scenario 1: The Runner’s Toe

Patient: A 34-year-old marathon runner.
Complaint: Painful dark blister under the nail of the right second toe after running a 10-mile race.
Diagnosis: Subungual hematoma (blood blister under the nail) from repetitive friction.

Correct code: S90.914 – Blister (nonthermal) of right lesser toe(s).

Alternative code (if under the nail): S90.913 – Blister (nonthermal) of other toe – but the first option is better.

Why not L60.8 (Nail disorder)? Because the cause is trauma, not a primary nail disease.

Scenario 2: The Toddler’s Pinched Finger

Patient: A 2-year-old child.
Complaint: Purple blister on the left ring fingertip after the child closed a cabinet door on it.
Diagnosis: Traumatic blood blister, noninfected.

Correct code: S60.422A – Blister (nonthermal) of left index finger. Wait – the ring finger is not the index finger. Correction: Use S60.429 – Blister of unspecified finger, because the EHR system does not have a specific code for “ring finger.” Most coders accept S60.429 as valid.

Better code: S60.429 is fine, or S60.429A for initial encounter.

Scenario 3: The Diabetic Patient with an Infected Blood Blister on the Foot

Patient: A 68-year-old with type 2 diabetes.
Complaint: Blood blister on the plantar surface (sole) of the left foot from new work boots. The blister opened, and now the area is red, warm, and draining yellow fluid.
Diagnosis: Infected blister.

Codes:

1. S90.912 – Blister (nonthermal) of left great toe (assuming the blister is on the toe – adjust if on sole)

2. L03.119 – Cellulitis of foot

3. E11.9 – Type 2 diabetes mellitus without complications (to show the patient’s underlying condition, because infections heal poorly in diabetics)

Critical note for diabetic patients: A small infected blood blister on a diabetic foot can become a limb-threatening emergency. Do not ignore it. Seek medical care immediately.

Scenario 4: The Mystery Recurrent Blood Blister

Patient: A 45-year-old woman with no history of injury.
Complaint: Recurring blood blisters on both palms for six months. They appear spontaneously, last a few days, then disappear.
Diagnosis: After workup, diagnosed with a mild form of epidermolysis bullosa acquisita.

Correct code: Q81.8 – Other epidermolysis bullosa.

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Complete ICD-10 Code List for Blood Blisters (Reference Table)

Here is a clean, searchable reference table. Use this as your quick guide.

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Common Coding Mistakes and How to Avoid Them

Even experienced coders can get tripped up. Here are the top five errors I see with blood blister coding.

Mistake #1: Using a burn code

Wrong: T20.0XXA – Burn of unspecified degree of head and neck.

Why it’s wrong: A blood blister is not a burn. Using a burn code can trigger a DRG (Diagnosis Related Group) for burn care, which changes reimbursement entirely.

Fix: Always use “nonthermal blister” codes from Chapter 19 (S00–T88).

Mistake #2: Using a generic rash code

Wrong: R21 – Rash and other nonspecific skin eruption.

Why it’s wrong: R21 is for undiagnosed rashes. You have a known diagnosis (traumatic blood blister).

Fix: Use the specific injury code.

Mistake #3: Forgetting the external cause code for workers’ comp

If the blood blister happened at work (e.g., a roofer pinching a finger with a shingle), you often need an external cause code for workers’ compensation claims.

Example:

• S60.429 (blister)

• W24.0XXA (contact with lifting devices, not elsewhere classified – or more specifically, W50.1 for striking against a stationary object)

Important: Most private insurance does not require external cause codes. But workers’ comp almost always does. Check your payer guidelines.

Mistake #4: Not documenting laterality

“Unspecified” codes (like S60.429) are fine for quick visits. But if you have the information, use a laterality code (right vs. left). This improves quality metrics and reduces audit risk.

Mistake #5: Coding a ruptured blister as a blister

Once the blister roof is gone, it is no longer a blister. It is an open wound. Switch to an S61 or S91 open wound code.

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How to Document a Blood Blister for Accurate Coding (For Clinicians)

Doctors and nurses: You hold the power to make coding easy or hard. Here is exactly what to write in your note.

A good blood blister documentation includes:

1. Location – Be specific. “Right fifth finger, distal phalanx, volar surface.”

2. Cause – “Pinch from car door” or “friction from new running shoes.”

3. Size – “Approximately 5 mm in diameter.”

4. Contents – “Dark red fluid; no pus.”

5. Complications – “No signs of infection. Roof intact.”

6. Laterality – “Left foot.”

7. Encounter number – “Initial encounter.”

Example note:

“The patient presents with a 4 mm blood blister on the volar pad of the left index finger. The injury occurred two hours ago when the patient’s finger was pinched in a household drawer. The blister roof is intact. No erythema, warmth, or purulent drainage. Diagnosis: Traumatic nonthermal blister. Plan: Protect blister, monitor for infection. Initial encounter.”

That single note gives a coder everything needed to assign S60.422A correctly.

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Frequently Asked Questions (FAQ)

Q1: Is there an exact ICD-10 code called “blood blister”?

No. ICD-10 does not have a code with the exact phrase “blood blister.” You must use “blister (nonthermal)” codes plus the specific body location.

Q2: Can I use L98.9 (skin disorder) for a blood blister?

Only if the blister is recurrent and no cause is found after a full workup. For a simple traumatic blister, using L98.9 would be incorrect and could be flagged as unbundling.

Q3: Do I need a separate code for the injury that caused the blood blister?

For regular medical insurance (Medicare, Blue Cross, Aetna), no. The S-code already implies trauma. For workers’ compensation, yes – you usually need an external cause code from Chapter 20 (V00–Y99).

Q4: What if the blood blister is from frostbite?

Frostbite is coded differently. Use T33–T34 codes. For example, T33.829 – Frostbite with tissue necrosis of unspecified foot. Do not use blister codes for frostbite.

Q5: How long does a blood blister take to heal for coding follow-up?

Most heal in 7–14 days. A subsequent encounter code (like S60.429D) is used if the patient returns for a scheduled recheck or if complications develop.

Q6: Can a blood blister be coded as a hematoma?

Sometimes. A hematoma is a collection of blood under the skin. A blood blister is a specific type of superficial hematoma. But ICD-10 treats them differently. Use L76.3 for a post-procedural hematoma, not for a traumatic blood blister. Stick with S-codes for trauma.

Q7: What if the patient has a bleeding disorder and gets blood blisters easily?

Then the blister is a manifestation of the bleeding disorder. Code the underlying condition first (e.g., D68.9 for coagulopathy, unspecified), then the blister code second. Example: D68.9, S60.429.

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Additional Resources for Medical Coders

For further reading and official guidance, I recommend these trusted sources:

• ICD-10-CM Official Guidelines for Coding and Reporting – The definitive rulebook. Read the chapter on “Injuries (S00–T88).”

• AHA Coding Clinic for ICD-10-CM – This is the gold standard for tricky cases. Search their archives for “blister” and “hematoma.”

• AAPC (American Academy of Professional Coders) – They offer excellent webinars on wound and blister coding.

Link to official resource:
➡️ https://www.cdc.gov/nchs/icd/icd10cm.htm
*(This is the US Centers for Disease Control and Prevention’s official ICD-10-CM page. It contains the complete code set and official guidelines.)*

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Final Summary (Conclusion)

Let’s wrap this up in three clear lines:

1. There is no single “blood blister” code – use “blister (nonthermal)” codes from the S60 (hand) or S90 (foot) families based on the blister’s location.

2. Always document the cause, location, laterality, and any complications like infection (add L08.9) or rupture (switch to an open wound code).

3. Never use burn codes for blood blisters, and always check payer requirements – especially for workers’ comp, which needs external cause codes.

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Disclaimer: This article is for informational and educational purposes only. Medical coding guidelines change frequently. Always consult the latest official ICD-10-CM manual and your local payer policies before submitting claims. This content does not constitute legal or medical advice. If you are a patient with a blood blister that is painful, large, or showing signs of infection, please see a healthcare provider.