# Can Illumina and IDT for Illumina DNA/RNA UD Indexes be used with the 16S Metagenomics Protocol?

**Yes**, the Illumina DNA/RNA Unique Dual (UD) Indexes and IDT for Illumina DNA/RNA UD Indexes can be used with the [Illumina 16S Metagenomic Sequencing Library Protocol](https://support.illumina.com/downloads/16s_metagenomic_sequencing_library_preparation.html). These indexes are compatible with the overhang sequences added in the first PCR step of the workflow.

When using the Illumina or IDT for Illumina DNA/RNA UD Indexes for the 16S workflow, use 10 µl of the pre-combined index primers per sample, rather than 5 µl each of the i5 and i7 Nextera XT index primers.

**Note:** The Illumina and IDT for Illumina DNA/RNA UD Indexes are 10 bp each; whereas, the Nextera XT indexes are 8 bp each.

\
\
\ <br>

|                                                                                                                                                                                                                                                                                                                                                                              |
| :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------: |
| *For any feedback or questions regarding this article (Illumina Knowledge Article #5766), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000005766%20-%20Library%20Preparation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://knowledge.illumina.com/library-preparation/amplicon-library-prep/library-preparation-amplicon-library-prep-faq-list/000005766.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.