Table A1.

Modified BIOCROSS quality rating tool.

Domain	IC	Recommendation	Included/Excluded	Changes/Justification
Study Rational
Hypothesis/Objective	1	1.1 Was the biomarker under study described?	Included	Was the outcome measure of mitochondrial dysfunction described?
		1.2 Was the rational for the study (research questions) clearly stated?	Included
		1.3 Were the study objectives/hypothesis clearly stated?	Included
Design/Methods
Study population selection	2	2.1 Were the characteristics of the study population presented?	Included
		2.2 Were the disease stages or comorbidities of the included participants described?	Included	Were diabetes and DKD status of the included participants described?
		2.3 Were the inclusion and exclusion criteria for study participation defined?	Included
Study population representativeness	3	3.1 Was the sampling frame reported (study population source)?	Included	Was the sampling frame reported for samples used to assess mitochondrial dysfunction?
		3.2 Was the participation rate reported (i.e., eligible persons at least 50%)?	Excluded	Not applicable as the only outcome of interest was group differences between NDC, DC, and DKD.
		3.3 Was sample size justification or power description provided?	Excluded	Not applicable for analysis.
Data analysis
Study population characteristics	4	4.1 Were the study population characteristics (i.e., demographic, clinical, and social) presented?	Excluded	Considered to repeat 2.1.
		4.2 Were the exposures and potential confounders described?	Included
		4.3 Were any missing values and strategies to deal with missing data reported?	Excluded	Not applicable for analysis.
Statistical analysis	5	5.1 Did the authors clearly report statistical methods used to calculate estimates (e.g., Spearman/Pearson/Linear Regression, etc.)?	Included	Were statistical methods used to identify group differences clearly reported?
		5.2 Were key potential confounding variables measured and adjusted statistically in reported analysis?	Excluded	Not applicable for analysis.
		5.3 Was the raw effect size estimate (correlation coefficient, beta coefficient) or measure of study precision provided (e.g., confidence intervals, precise (1) p-value)?	Included	Was the p-value reported to distinguish group differences?
Data interpretation
Interpretation and evaluation of results	6	6.1 Was the data discussed in the context of study objectives/hypothesis?	Included
		6.2 Was the interpretation of the results considering findings from similar studies?	Included
		6.3 Was the biological context described?	Included
Study limitations	7	7.1 Was the cross-sectional nature of the analysis discussed	Excluded	Not applicable as the only outcome of interest was group differences between NDC, DC, and DKD.
		7.2 Did the authors acknowledge restricted interpretation due to measurements at one point in time and no statement about causality possible using cross-sectional studies?	Excluded	Not applicable as the only outcome of interest was group differences between NDC, DC, and DKD, not possible causality.
		7.3 Did the authors acknowledge need for consistency with other research?	Included
Biomarker measurement
Specimen characteristics and assay methods	8	8.1 Were the measurement methods described? (assay methods, preservation and storage, detailed protocol, including specific reagents or kits used)	Included	Were the method(s) used to assess mitochondrial dysfunction adequately described?
		8.2 Were the reproducibility assessments performed for evaluating biomarker stability?	Excluded	Not applicable as the only outcome of interest was group differences between NDC, DC, and DKD.
		8.3 Were the quantitation methods well described?	Excluded	Not applicable for analysis.
Laboratory measurement	9	9.1 Was the laboratory/place of measurement mentioned?	Included
		9.2 Were any quality control procedures and results reported (e.g., reported coefficient of variation?	Excluded	Not applicable as the only outcome of interest was group differences between NDC, DC, and DKD.
		9.3 Were the analysis blinded for laboratory staff?	Included
Biomarker data modelling	10	10.1 Was the distribution of biomarker data reported (if non-normal how was it standardised)?	Excluded	Not applicable as the only outcome of interest was group differences between NDC, DC, and DKD.
		10.2 Did the authors report on methods or outlier detection and handling?	Included
		10.3 Were any possible errors resulting from measurement inaccuracies discussed?	Included

DC, diabetic control without DKD; DKD, diabetic kidney disease; IC, Issues to consider; NDC non-diabetic control.