---
title: IgBLAST outputs and interpretation
description: Germline V gene hits and framework-mutation counts from IgBLAST, for amino-acid antibody sequences.
tags:
  - igblast
  - outputs
---

IgBLAST returns, per amino-acid sequence, the ranked V germline gene hits with alignment statistics, the top V gene, its percent identity, the chain type, and the number of framework mismatches against germline (somatic hypermutation). D and J are not searched, and the CDR3, productivity and stop-codon status are not determined; each of those fields is null and its reason is listed under `undetermined`. Read the top V gene and its identity first: a low V-identity means the sequence has hypermutated far from germline, which is exactly what humanness scoring will care about.

## Per-sequence result

Each annotated sequence carries these fields:

| Field | Type | What it tells you |
|---|---|---|
| `sequence_name` | string | The name you gave the sequence. |
| `chain_type` | `VH` \| `VK` \| `VL` \| null | Heavy, kappa-light, or lambda-light. |
| `v_gene_hits` | list | Ranked V-gene hits, each with `gene_name`, `identity_pct`, `evalue`, `score`, `alignment_length`. |
| `d_gene_hits` | list | Ranked D-gene hits (same shape). ⊘ Always empty here: D is not searched. |
| `j_gene_hits` | list | Ranked J-gene hits (same shape). ⊘ Always empty here: J is not searched. |
| `top_v_gene` | string \| null | The best-scoring V gene. |
| `top_d_gene` | string \| null | The best-scoring D gene. ⊘ Always null here. |
| `top_j_gene` | string \| null | The best-scoring J gene. ⊘ Always null here. |
| `v_identity_pct` | float \| null | Percent identity of the top V-gene alignment. |
| `cdr3_sequence` | string \| null | The CDR3 amino-acid sequence. ⊘ Always null here: the CDR3 end needs the J gene. |
| `cdr3_length` | int \| null | Length of the CDR3. ⊘ Always null here. |
| `framework_mutations` | int \| null | Amino-acid mismatches against the germline V gene in the framework regions (somatic hypermutation). |
| `productive` | bool \| null | Whether the rearrangement is productive. ⊘ Always null here. |
| `stop_codon` | bool \| null | Whether a stop codon was detected. ⊘ Always null here. |
| `segments_searched` | string[] | The germline segments searched: `["V"]`. |
| `undetermined` | object | For each field above that is null or empty, the reason it was not determined. |

## Job-level summary

| Field | Type | Meaning |
|---|---|---|
| `failed_sequences` | string[] | Sequences IgBLAST could not annotate. |
| `success_count` | int | Sequences annotated successfully. |
| `fail_count` | int | Sequences that failed. |
| `organism` | string | Germline database used. |
| `domain_system` | string | Domain system applied (`imgt` or `kabat`). |
| `sequence_type` | `protein` | The input type the job ran. ⊘ Always `protein` on this platform — nucleotide input is refused, so `nucleotide` is never returned. |

## Reading the result card

The IgBLAST result renders on the canvas as an antibody-structure annotation card, surfacing the top V gene and its identity so you can read the germline lineage at a glance.

## What to do next

- A low `v_identity_pct` or high `framework_mutations` flags a hypermutated sequence — send it to [Humatch](/docs/humatch) or [BioPhi](/docs/biophi) for humanness scoring.
- Get the CDR3 and region boundaries from [ANARCI](/docs/anarci), then use the CDR3 for repertoire mining with [OAS search](/docs/oas-search).
- Number the sequence to a canonical scheme with [ANARCI](/docs/anarci).

## Read next