Intra-day variability of cystatin C, creatinine and estimated GFR in intensive care patients.
BACKGROUND
Markers of renal function are widely used in intensive care and sudden changes are important indicators of acute kidney injury. The problem is to distinguish between disease progression/improvement from the natural variation in the patient. The aim of the present study was thus to study the normal intraday variation in ICU patients.


METHODS
We studied the intra-day variation of creatinine, cystatin C and estimated GFR based on these two markers in 28 clinically stable ICU patients.


RESULTS
The median diurnal coefficient of variation sCV) for creatinine was 3.70% (1.92-9.25%) while the median CV for cystatin C was 3.66% (1.36-8.11%). The corresponding CVs for the estimated GFRs were 2.00% (0.89-9.82%) for eGFRcreatinine and 4.60% (1.65-10.24%) for eGFRcystc.


CONCLUSIONS
The eGFRcreatinine values in individual patients were clearly higher than the eGFRcystc values. The median CV for creatinine, cystatin C and the eGFR measurements were below 5% which means that 95% of the test results will vary by <10% between sampling times in stable ICU patients. Differences >10% between sampling times are thus likely to be an indication of changes in biomarker levels due to the disease/treatment.
Section of Anaesthesia and Intensive Care Medicine, Department of Physiology and Pharmacology, Karolinska Institutet, 17176 Stockholm, Sweden.
Bo
B
Ravn
Clinical Chemistry, Department of Medical Sciences, Uppsala University, 751 85 Uppsala, Sweden.
Anders
A
Larsson
Section of Anaesthesia and Intensive Care Medicine, Department of Physiology and Pharmacology, Karolinska Institutet, 17176 Stockholm, Sweden; Department of Intensive Care, Austin Hospital, Heidelberg, Melbourne, VIC 3084, Australia.
Johan
J
Mårtensson
Section of Anaesthesia and Intensive Care Medicine, Department of Physiology and Pharmacology, Karolinska Institutet, 17176 Stockholm, Sweden.
Claes-Roland
CR
Martling
Section of Anaesthesia and Intensive Care Medicine, Department of Physiology and Pharmacology, Karolinska Institutet, 17176 Stockholm, Sweden. Electronic address: max.bell@karolinska.se.
Max
M
Bell
D058186:Acute Kidney Injury / Q000097:blood*; D002940:Circadian Rhythm; D003404:Creatinine / Q000097:blood; D003422:Critical Care / Q000379:methods*; D055316:Cystatin C / Q000097:blood; D005919:Glomerular Filtration Rate; D006801:Humans; D007677:Kidney Function Tests
D055316:Cystatin C; D003404:Creatinine
Creatinine; Critical illness; Cystatin C; Renal markers