Sample Type Identifier
What is Sample Type?
Sample Type refers to the classification of biological samples based on their origin, source, or biological matrix. In omics studies, sample type identifies what kind of biological material was collected and analyzed.
Common Sample Types in CMMI-DCC
Human Clinical Samples
Blood-Derived Samples
- Plasma: Liquid portion of blood without cells (contains proteins, metabolites)
- Serum: Liquid portion after blood coagulation (similar to plasma, without clotting factors)
- Whole Blood: Complete blood with all components
- PBMC: Peripheral Blood Mononuclear Cells (immune cells)
Stool/Fecal Samples
- Primary Use: Microbiome and metagenomics analysis
- Contains: Gut bacteria, viruses, fungi, archaea
- Applications: Digestive health, disease biomarkers
Oral Samples
- Saliva: Mixed fluid from salivary glands
- Oral Swab: Surface sampling from mouth, tongue, or teeth
- Applications: Oral microbiome, systemic health markers
Skin Samples
- Skin Swab: Surface sampling from various body sites
- Applications: Skin microbiome, wound healing, dermatology
Tissue Samples
- Biopsy: Small tissue sample for analysis
- Formalin-Fixed: Preserved tissue for histology
- Frozen: Tissue preserved at low temperature for molecular analysis
Urine
- Applications: Metabolomics, kidney function, biomarkers
Environmental Samples
- Soil: Microbial communities in soil
- Water: Aquatic microbiomes (freshwater, marine)
- Air: Airborne microbial communities
Sample Type Implications
Microbiome Composition
Different body sites have distinct microbial communities:
- Gut: High diversity, dominated by Firmicutes and Bacteroidetes
- Oral: Moderate diversity, Streptococcus, Veillonella predominant
- Skin: Low diversity, Staphylococcus, Propionibacterium
Omics Data Characteristics
Proteomics
- Plasma/Serum: High-abundance proteins dominate; requires depletion strategies
- Tissue: Cell-type specific proteins; requires extraction optimization
- Urine: Lower protein content; concentrated metabolites
Metabolomics
- Plasma: Complex mixture; reflects systemic metabolism
- Urine: Concentrated metabolites; kidney filtration products
- CSF: Central nervous system metabolites
Microbiome
- Stool: Representative of gut microbiome
- Oral: Distinct community; airway and mouth microbiota
- Skin: Site-specific variations (moist vs. dry skin)
Sample Collection Considerations
Timing
- Fasting vs. Fed: Metabolite levels vary with meals
- Circadian Rhythm: Microbial composition changes throughout day
- Longitudinal: Multiple time points to track changes
Handling
- Immediate Processing: Some samples require rapid stabilization
- Preservation: Specific methods for different sample types
- Storage: -80C for molecular analyses, formalin for histology
Contamination
- Skin Microbiome: Can contaminate other samples during collection
- Environmental: Reagents and equipment can introduce contaminants
- Cross-Contamination: Between samples during processing
Sample Type in CMMI-DCC
In the CMMI Data Coordinating Center:
- Microbiome Studies: Stool, oral, and skin sample types
- Metagenomics: Fecal samples for gut microbiome
- Metabolomics: Plasma, serum, urine for metabolite profiling
- Proteomics: Plasma and tissue samples for protein analysis
- Filtering: Data can be filtered by sample type in results views
Why Sample Type Matters
- Biological Context: Results must be interpreted in context of source
- Reference Ranges: "Normal" values differ by sample type
- Plasma metabolites vs. urine metabolites
- Gut microbiome vs. oral microbiome
- Analysis Methods: Different protocols for different matrices
- Comparison Validity: Can only compare like-with-like
Sample Metadata
Related to sample type:
- Collection Date: When sample was collected
- Processing Date: When sample was processed
- Storage Conditions: Time and temperature before analysis
- Freeze-Thaw Cycles: Can affect sample quality
Related Terms
- Biofluid: Liquid biological samples (plasma, serum, urine)
- Matrix: The biological material containing analytes
- Specimen: Collected sample for analysis
- Cohort: Group of participants providing samples
Quality Considerations
- Sample Quality: Hemolysis (blood), degradation (RNA), contamination
- Quantity: Sufficient material for analysis
- Integrity: Preserved molecular structure
- Consistency: Uniform collection methods across study
References
- Biological sample collection protocols
- Sample type-specific processing methods
- Biobanking and sample preservation