Calculation of eGFR (cr–cys)
eGFR (cr–cys) is a combined estimated glomerular filtration rate derived from both serum creatinine (eGFRcr) and cystatin C (eGFRcys). It is designed to provide a more accurate and clinically robust estimate of kidney filtration than using either marker alone.
How is eGFR (cr–cys) calculated?
A blood sample is analyzed for both creatinine and cystatin C. eGFR is first estimated using each marker separately (eGFRcr and eGFRcys), and these results are then combined in a validated equation to produce a single value: eGFR (cr–cys). The result is reported as milliliters per minute per 1.73 m² of body surface area (mL/min/1.73 m²).
When is eGFR (cr–cys) a suitable choice?
- When you want a more reliable and balanced assessment of kidney function.
- When eGFR based on creatinine or cystatin C alone may be uncertain.
- In people with atypical muscle mass or factors that can influence creatinine-based estimates.
- When monitoring suspected or known impairment of kidney function over time.
How is the eGFR (cr–cys) result interpreted?
Higher eGFR (cr–cys) values generally correspond to better kidney function, while lower values may indicate reduced kidney filtration. Because eGFR (cr–cys) integrates two independent filtration markers, it often provides a more representative estimate of true kidney function and can reduce the risk of misclassification compared with using a single marker.
Limitations of eGFR (cr–cys)
Although eGFR (cr–cys) is generally more robust than single-marker estimates, it is still an estimated value and should be interpreted in a clinical context. If results are clearly abnormal or if there is clinical suspicion of kidney disease, further evaluation may be needed.
