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Cystatin C: unsuited to use as a marker of kidney function in the intensive care unit

Raymond Wulkan, Jan den Hollander, Arie Berghout

    Critical Care (London, England)
    |November 10, 2005
    PubMed

    Insights

    Cystatin C is not a reliable marker for glomerular filtration rate in critically ill patients. Its accuracy is compromised by factors like body mass, thyroid disorders, and the chosen threshold for renal dysfunction.

    Area of Science:

    • Nephrology
    • Critical Care Medicine
    • Clinical Chemistry

    Background:

    • The utility of cystatin C as a glomerular filtration rate (GFR) marker in critically ill patients is debated.
    • Previous studies have suggested cystatin C as a superior alternative to creatinine for GFR estimation.

    Discussion:

    • The 'gold standard' for GFR measurement in the original study (body surface corrected creatinine clearance) is unreliable in obese/lean patients common in intensive care.
    • The study's renal dysfunction cutoff (80 ml/min) deviates from the accepted standard (50 ml/min), potentially skewing results.
    • Exclusion of patients with thyroid disorders is problematic, as critical illness often mimics thyroid dysfunction and impacts cystatin C accuracy.

    Key Insights:

    • Cystatin C levels are inversely affected by thyroid dysfunction (low in hypothyroidism, high in hyperthyroidism), rendering it unsuitable for GFR assessment in these cases.
    • Creatinine clearance, used as a comparator, has limitations in extreme body compositions (obesity, leanness).
    • Discrepancies in GFR assessment thresholds and patient selection criteria raise concerns about cystatin C's applicability in intensive care settings.

    Outlook:

    • Further validation of GFR markers in critically ill populations with diverse physiological states is warranted.
    • Standardization of GFR assessment methodologies, including the choice of 'gold standard' and diagnostic cutoffs, is crucial for reliable clinical interpretation.
    • Investigating alternative or adjusted biomarkers that account for critical illness-related physiological changes may be necessary.

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