---
title: "How do I Create a Custom Regex for Medical Record Numbers (MRNs)?"
url: "https://dm0bkdes5q7a2ls.productfruits.help/en/article/743f3edd-b319-4df1-98e4-d462cebcdcc9"
language: "en"
last_updated: "2026-10-05T14:56:49.601Z"
---

# How do I Create a Custom Regex for Medical Record Numbers (MRNs)?

To create a custom regex for Medical Record Numbers (MRNs), you need to define a Custom Data Type in the Spirion Console.

Because MRN formats vary significantly between healthcare providers (for example, Epic vs. Cerner vs. legacy systems), a custom RegEx is the most accurate way to detect them.

### Step 1: Define the Pattern

First, identify the exact structure of your MRNs.

-   **Example A (Simple Numeric):** `12345678` (8 digits)
-   -   Regex: `\b\d{8}\b`
-   **Example B (Alphanumeric with Prefix):** `MRN-12345`
-   -   Regex: `\bMRN-\d{5}\b`
-   **Example C (Complex):** `AB-123-45`
-   -   Regex: `\b[A-Z]{2}-\d{3}-\d{2}\b`

### Step 2: Create the Custom Data Type in the Console

Procedure:

1.  From the left-side navigation menu navigate to **Settings > Global Data Types > CUSTOM DATA TYPES tab**.
2.  Click **Actions > Add Custom Data Type**.
3.  Select **Regular Expression** from the drop-down menu.
4.  **Name:** Give it a clear name like `Custom MRN - [Hospital Name]`.
5.  **Regex Pattern:** Enter your pattern (for example, `\b\d{8}\b`).
6.  -   *Tip:* Always use `\b` (word boundaries) at the start and end to prevent matching a 8-digit string that is actually part of a longer number (like a phone number).
7.  **Validation (Optional but Recommended):**
8.  -   If your MRN has a checksum, you can use a **SearchAPI** script for advanced validation.
    -   Otherwise, rely on **Keywords** (see Step 3).

### Step 3: Add Context with Keywords (Reduce False Positives)

A 8-digit number regex will match *everything*—dates, serial numbers, and parts of zip codes. You **must** add keywords to ensure accuracy.

1.  In the same Custom Data Type definition, look for the **Keywords** section.
2.  Add terms such as the following: `MRN`, `Medical Record`, `Patient ID`, `Patient Number`, `Chart Number`.
3.  Set the **Proximity**: Require one of these keywords to be within **50 to 100 characters** of the RegEx match.

### Step 4: Test and Deploy

1.  **Test:** Use the "Test Regex" tool in the console (if available) or run a scan against a **single test file** containing known MRNs.
2.  **Add to Policy:** Go to your **Scan Policy**, navigate to **Sensitive Data Types**, and check the box for your new `Custom MRN` type.
3.  **Run Scan:** Execute the scan and review the **Match Evidence** to ensure it is picking up the MRNs correctly without too much noise.

* * *

### Best Practice: The "SDD" Upgrade

Once your regex is working, wrap it in a **Sensitive Data Definition (SDD)**.

-   Create a Sensitive Data Definition called **"Confirmed PHI"**.
-   Logic: `(Custom MRN Regex) NEAR (Patient Name AnyFind).`
-   **Why:** This ensures that you only alert on files where an MRN is actually associated with a person, which is the true definition of PHI under HIPAA.

## **Summary**

Use a **Custom Regex Data Type** with word boundaries (`\b`), add **Keywords** for context, and eventually combine it with **AnyFinds** in a **Sensitive Data Definition** for the highest possible accuracy.