Performs quality control on single-cell RNA-seq data (.h5ad or .h5 files) using scverse best practices with MAD-based filtering and comprehensive visualizations. Use when users request QC analysis, filtering low-quality cells, assessing data quality, or following scverse/scanpy best practices for single-cell analysis.
Streamline single-cell sequencing data preparation by automatically removing low-quality cells to ensure reliable findings. You receive clear visual reports showing data quality and a refined dataset ready for further analysis. Use this whenever you need to check data integrity or prepare raw files before starting your research.
name: single-cell-rna-qc
description: Performs quality control on single-cell RNA-seq data (.h5ad or .h5 files) using scverse best practices with MAD-based filtering and comprehensive visualizations. Use when users request QC analysis, filtering low-quality cells, assessing data quality, or following scverse/scanpy best practices for single-cell analysis.
Single-Cell RNA-seq Quality Control
Automated QC workflow for single-cell RNA-seq data following scverse best practices.
When to Use This Skill
Use when users:
Request quality control or QC on single-cell RNA-seq data
Want to filter low-quality cells or assess data quality
Need QC visualizations or metrics
Ask to follow scverse/scanpy best practices
Request MAD-based filtering or outlier detection
Supported input formats:
.h5ad files (AnnData format from scanpy/Python workflows)
.h5 files (10X Genomics Cell Ranger output)
Default recommendation: Use Approach 1 (complete pipeline) unless the user has specific custom requirements or explicitly requests non-standard filtering logic.
Approach 1: Complete QC Pipeline (Recommended for Standard Workflows)
For standard QC following scverse best practices, use the convenience script scripts/qc_analysis.py:
python3 scripts/qc_analysis.py input.h5ad# or for 10X Genomics .h5 files:python3 scripts/qc_analysis.py raw_feature_bc_matrix.h5
The script automatically detects the file format and loads it appropriately.
When to use this approach:
Standard QC workflow with adjustable thresholds (all cells filtered the same way)
Apply MAD-based filtering - Permissive outlier detection using MAD thresholds for counts/genes/MT%
Filter genes - Remove genes detected in few cells
Generate visualizations - Comprehensive before/after plots with threshold overlays
Approach 2: Modular Building Blocks (For Custom Workflows)
For custom analysis workflows or non-standard requirements, use the modular utility functions from scripts/qc_core.py and scripts/qc_plotting.py:
# Run from scripts/ directory, or add scripts/ to sys.path if neededimport anndata as adfrom qc_core import calculate_qc_metrics, detect_outliers_mad, filter_cellsfrom qc_plotting import plot_qc_distributions # Only if visualization neededadata = ad.read_h5ad('input.h5ad')calculate_qc_metrics(adata, inplace=True)# ... custom analysis logic here
When to use this approach:
Different workflow needed (skip steps, change order, apply different thresholds to subsets)
Conditional logic (e.g., filter neurons differently than other cells)
Partial execution (only metrics/visualization, no filtering)
Integration with other analysis steps in a larger pipeline
Custom filtering criteria beyond what command-line params support
Load this reference when users need deeper understanding of the methodology or when troubleshooting QC issues.
Next Steps After QC
Typical downstream analysis steps:
Ambient RNA correction (SoupX, CellBender)
Doublet detection (scDblFinder)
Normalization (log-normalize, scran)
Feature selection and dimensionality reduction
Clustering and cell type annotation
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scverse Quality Control Guidelines
This document provides detailed information about quality control best practices for single-cell RNA-seq data, following the scverse ecosystem recommendations.
Quality Control Metrics
Count Depth (Total Counts)
What it measures: Total number of UMI/reads per cell
Why it matters: Low count cells may be empty droplets, debris, or poorly captured cells
Typical range: 500-50,000 counts per cell (varies by protocol)
Red flags: Bimodal distributions may indicate mixing of high and low-quality cells
Gene Detection (Genes per Cell)
What it measures: Number of genes with at least 1 count
Why it matters: Strongly correlates with count depth; low values indicate poor capture
Typical range: 200-5,000 genes per cell
Red flags: Very low values (<200) suggest technical failures
Mitochondrial Content
What it measures: Percentage of counts from mitochondrial genes
Why it matters: High MT% indicates cell stress, apoptosis, or lysed cells
Typical range: <5% for most tissues, up to 10-15% for metabolically active cells
Species-specific patterns:
Mouse: Genes start with 'mt-' (e.g., mt-Nd1, mt-Co1)
Human: Genes start with 'MT-' (e.g., MT-ND1, MT-CO1)
Context matters: Some cell types (cardiomyocytes, neurons) naturally have higher MT content
Ribosomal Content
What it measures: Percentage of counts from ribosomal protein genes
Why it matters: Can indicate cell state or contamination
Patterns: Genes start with 'Rpl'/'RPL' (large subunit) or 'Rps'/'RPS' (small subunit)
Note: High ribosomal content isn't always bad - metabolically active cells have more ribosomes
Hemoglobin Content
What it measures: Percentage of counts from hemoglobin genes
Why it matters: Indicates blood contamination in non-blood tissues
Patterns: Genes matching '^Hb[^(p)]' or '^HB[^(P)]' (excludes Hbp1/HBP1)
When to use: Particularly important for tissue samples (brain, liver, etc.)
MAD-Based Filtering Rationale
Why MAD Instead of Fixed Thresholds?
Fixed thresholds (e.g., "remove cells with <500 genes") fail because:
Different protocols yield different ranges
Different tissues have different characteristics
Different species have different gene counts
Fixed thresholds are arbitrary and not data-driven
MAD (Median Absolute Deviation) is robust to outliers and adapts to your dataset: