Improving Patient Assessment After Acute Kidney Injury (AKI)

• Iohexol renal clearance measurement (Diagnostic test): Gold standard measurement of glomerular filtration rate.
• Cystatin C (Diagnostic test): Estimated GFR using serum cystatin C
• Creatinine (Diagnostic test): eGFR from serum creatinine level
• Semi structured interview (Other): Semi structured interview to explore patient experiences. Purposive sampling will be used to explore a wide range of perspectives and transcripts will be analysed using thematic analysis to develop codes and themes.
• Participatory workshop (Other): Group workshop using qualitative methods. Purposive sampling will be used to explore a wide range of perspectives and transcripts will be analysed using thematic analysis to develop codes and themes. These will be used to develop consensus recommendations.
• Metagenome analysis (Diagnostic test): Analysis of the metagenome using faecal samples of participants after acute kidney injury
• Bioimpedance analysis (Diagnostic test): Estimation of body composition
• Patient reported outcome measures (Other): EQ-5D-5L, KSQ, WHO-DAS 2.0, K10
• Measurement of physical performance (Other): Hand grip, Short physical performance battery

Primary outcomes

• The proportion of eligible patients who agree to participate [3 months]
• The proportion of participants who have all three measurements (eGFR-cystatin, eGFR-creatinine and measured GFR) [3 months]
• Standard deviation of the difference between measured GFR and eGFR-creatinine and eGFR-cystatin [3 months]
• The proportion of patients with eGFR <60ml/min/1.73m2 from eGFR-cystatin compared with eGFR creatinine [3 months]
• Gut microbiome composition [3 months]: Assessed through metagenomics
• Codes and themes related to patient experience after AKI, identified from systematic qualitative analysis of interview transcripts [3 - 12 months]
• Production of a document of recommended next steps through MDT development during participatory workshops [At completion of third workshop 3 years after enrolment]

Secondary outcomes

• The mean difference between eGFR-cystatin and eGFR-creatinine [3 months]
• The mean difference between iohexol measured GFR and each estimated GFR method (creatinine and cystatin) [3 months]
• Correlation between eGFR creatinine and eGFR cystatin [3 months]
• Correlation between iohexol measured GFR and each estimated GFR method (creatinine and cystatin) [3 months]
• Bias between iohexol measured GFR and each estimated GFR method (creatinine and cystatin) [3 months]
• Accuracy of eGFR creatinine and eGFR cystatin compared with iohexol measured GFR as assessed by the percentage of estimated values within 30% of measured GFR (P30) [3 months]
• Correlation of muscle mass with the percentage difference between eGFR-cystatin and eGFR-creatinine [3 months]
• Correlation of physical function with the percentage difference between eGFR-cystatin and eGFR-creatinine [3 months]
• Correlation of patient reported outcomes with the percentage difference between eGFR-cystatin and eGFR-creatinine [3 months]
• Barriers to implementation of recommendations as identified through MDT discussion at participatory workshops [At completion of third workshop 3 years after enrolment]

Other outcomes

• Safety Outcomes [From enrolment until the end of study visits (from 3 to 12 months)]: * Adverse events spontaneously reported during the study * Discontinuation due to adverse events

Sex: All, ages: 18 Years to 85 Years

Inclusion Criteria:

Observational study workstream

* Age 18-85 years
* AKI stage 2 or 3 during hospital admission OR AKI stage 1 of at least 7 days duration during hospital admission
* 60-90 days after peak creatinine Qualitative interview workstream
* Age 18-85 years
* AKI during hospital admission
* 60-90 days after peak creatinine Participatory workshop workstream
* Age 18-85 years
* Relevant experience (as assessed by the investigator) which could include personal experience of an episode of hospitalised AKI as a patient of carer, experience of managing AKI or related problems in a professional capacity or knowledge of a particular community.

Exclusion Criteria:

Observational study workstream

* Inability to give informed consent
* No baseline creatinine available in previous 12 months
* Pregnancy or breastfeeding
* Current treatment with dialysis
* Renal transplant
* Pacemaker in situ
* Previous amputation
* Allergy to Omnipaque contrast agent (WP1 only)
* Manifest thyrotoxicosis (WP1 only)
* Ascites or significant (grade 3 to 4) peripheral oedema, defined as ≥6 mm pit, lasting for >1 minute after 5-second compression over tibia or medial malleolus (WP1 only) Qualitative interview workstream
* Inability to give informed consent
* No baseline creatinine available in previous 12 months
* Current treatment with dialysis
* Renal transplant
* Receiving palliative care Participatory workshop workstream
* Inability to give informed consent
* Inability to communicate in English (the qualitative workshops will be held in English)

• Nicholas Selby, Principal investigator, University of Nottingham