Unified Data Dictionary

This standardized data dictionary documents the common variables shared across all Orca datasets within G-Trac. These variables have been harmonized to enable cross-study analyses while preserving study-specific details.

Note: Each study dataset also includes study-specific fields documented separately: - GI-DAMPs Columns - MUSIC Columns - Mini-MUSIC Columns

Naming Convention

All variables in Orca datasets follow the snake_case naming convention: - All characters are lowercase - Words are separated by underscores - No spaces or special characters (except underscores) - Examples: study_id, nhs_bloods_date, hbi_total

Variable Organization

The sections below group the shared fields into logical themes to help you quickly find related variables across datasets. For study-specific variables, refer to the individual dataset column lists.

Demographics & Visit Context

Variable	Type	Values	Comments
study_id	string		Study-specific participant identifier using prefixes such as GID-, MID-, or MINI-.
study_group	string	cd, uc, ibdu, non_ibd, await_dx, hc	Disease classification at the visit: Crohn's disease (cd), Ulcerative colitis (uc), IBD unclassified (ibdu), non-IBD control, awaiting diagnosis, or healthy control.
study_center	string	edinburgh, glasgow, aberdeen, dundee	Recruiting centre recorded for the visit.
sex	string	male, female	Participant sex recorded by the study.
age	int		Participant age in years at the time of the visit.
age_at_diagnosis	int		Age in years when inflammatory bowel disease was first diagnosed.
date_of_diagnosis	date	YYYY-MM-DD	Calendar date when inflammatory bowel disease was first diagnosed.
has_active_symptoms	string	1 / 0 or yes / no	Indicator of active symptoms at the visit; recorded as 1/0 or yes/no depending on source system.
height	int		Height measured in centimetres.
weight	float		Weight measured in kilograms.
bmi	float		Body mass index calculated as kg/m^2.

Laboratory Values

Variable	Type	Values	Comments
nhs_bloods_date	date	YYYY-MM-DD	Date the NHS blood panel was collected.
haemoglobin	float		Haemoglobin concentration (g/L) from NHS bloods.
haematocrit	float		Haematocrit reported as a proportion (L/L).
white_cell_count	float		Total white cell count (x10^9/L) from NHS bloods.
neutrophils	float		Absolute neutrophil count (x10^9/L) from NHS bloods.
lymphocytes	float		Absolute lymphocyte count (x10^9/L) from NHS bloods.
monocytes	float		Absolute monocyte count (x10^9/L) from NHS bloods.
basophils	float		Absolute basophil count (x10^9/L) from NHS bloods.
eosinophils	float		Absolute eosinophil count (x10^9/L) from NHS bloods.
platelets	int		Platelet count (x10^9/L) from NHS bloods.
sodium	float		Serum sodium (mmol/L) from NHS bloods.
potassium	float		Serum potassium (mmol/L) from NHS bloods.
urea	float		Serum urea (mmol/L) from NHS bloods.
creatinine	float		Serum creatinine from NHS bloods, measured in umol/L.
albumin	float		Serum albumin from NHS bloods, measured in g/L.
crp	float		C-reactive protein (mg/L) from NHS bloods.
calprotectin	string	numeric or threshold string (e.g., <20, >1800, no sample)	Faecal calprotectin result (ug/g) reported as numeric values or qualitative thresholds by the laboratory.
calprotectin_date	date	YYYY-MM-DD	Date the faecal calprotectin sample was collected.

IBD Phenotyping

Variable	Type	Values	Comments
baseline_eims_none	int	1 yes, 0 no	Baseline survey response confirming no extra-intestinal manifestations were reported.
baseline_eims_episcleritis	int	1 yes, 0 no	Baseline record indicating a history of episcleritis as an extra-intestinal manifestation.
baseline_eims_erythema_nodosum	int	1 yes, 0 no	Baseline record indicating erythema nodosum as an extra-intestinal manifestation.
baseline_eims_pyoderma	int	1 yes, 0 no	Baseline record indicating pyoderma gangrenosum as an extra-intestinal manifestation.
baseline_eims_sacroileitis	int	1 yes, 0 no	Baseline record indicating sacroiliitis as an extra-intestinal manifestation.
baseline_eims_uveitis	int	1 yes, 0 no	Baseline record indicating uveitis as an extra-intestinal manifestation.
previous_appendicectomy	int	1 yes, 0 no	History of appendicectomy recorded at baseline.
previous_tonsillectomy	int	1 yes, 0 no, -1000 unknown	History of tonsillectomy recorded at baseline; -1000 is used where the source study captured an explicit unknown response.

IBD Medications & Monitoring

Variable	Type	Values	Comments
sampling_asa	int	1 yes, 0 no	Aminosalicylates (5-ASA) were being taken at the time of sampling.
sampling_ada	int	1 yes, 0 no	Adalimumab was being taken at the time of sampling.
sampling_ifx	int	1 yes, 0 no	Infliximab was being taken at the time of sampling.
sampling_mtx	int	1 yes, 0 no	Methotrexate was being taken at the time of sampling.
sampling_uste	int	1 yes, 0 no	Ustekinumab was being taken at the time of sampling.
sampling_vedo	int	1 yes, 0 no	Vedolizumab was being taken at the time of sampling.
drug_level_date	date	YYYY-MM-DD	Date the therapeutic drug monitoring sample (for biologic drug or antibody levels) was taken.
ada_level	string	assay result in ug/mL (numeric or threshold string)	Measured adalimumab concentration from therapeutic drug monitoring; labs often report numeric levels or threshold strings such as >12.
ada_antibody	string	assay result (e.g., 5, <10, not_tested)	Anti-adalimumab antibody result captured during therapeutic drug monitoring; qualitative thresholds or numeric titres reported by the lab.
ifx_level	string	assay result in ug/mL (numeric or threshold string)	Measured infliximab concentration from therapeutic drug monitoring; labs report numeric values or thresholds such as >12.
ifx_antibody	string	assay result (e.g., 5, <10, not_detected)	Anti-infliximab antibody result from therapeutic drug monitoring; values include numeric titres or qualitative thresholds.

Investigations & Imaging

Variable	Type	Values	Comments
endoscopy_date	date	YYYY-MM-DD	Date of the most recent endoscopy associated with the visit.
endoscopy_report	string		Narrative endoscopy findings recorded in clinical notes.
pathology_report	string		Narrative pathology findings (e.g., biopsy results).
mri_small_bowel	int	1 performed, 0 not performed	Indicator that a small bowel MRI was completed for the visit.
mri_pelvis	int	1 performed, 0 not performed	Indicator that a pelvic MRI was completed for the visit.
mri_small_bowel_report	string		Narrative findings from the small bowel MRI report.