Revised Schwartz Equation for Glomerular Filtration Rate (GFR) (2009)
Use in infants, children, and adolescents with or without chronic kidney disease (CKD).
- Although the original formula was designed using data from a cohort of children without CKD, the revised equation (used here) has been shown to apply to populations of children with CKD with relatively high accuracy.
- This formula is inaccurate in acute kidney injury (AKI), as GFR in AKI has not reached a steady state. Only in children with normal renal function or established CKD does GFR reach a steady state that can be estimated by using this formula.
- Neonates have higher normal values of serum creatinine than do older infants and children, as maternal creatinine may circulate in the neonate for several days after birth. Children have lower normal levels of creatinine compared to adolescents and adults because of their smaller muscle mass. Use caution in interpreting serum creatinine levels in children, as levels considered normal in adults and adolescents may be elevated and indicative of impaired renal function in younger children.
- A k value of 0.413 is more accurate for labs that use enzymatic methods (as opposed to the Jaffe method) to determine serum creatinine levels.
- Determines stage and severity of kidney dysfunction in children.
- Helps in adjusting medication doses according to renal function.
- Can provide prognostic information for children with CKD and identify potential candidates for renal replacement therapy (generally, eGFR <15).
- The newer CKiD equation, which requires BUN and cystatin-C in addition to serum creatinine, may overestimate GFR, as cystatin-C is not as well standardized as serum creatinine. Cystatin-C is also less widely available than serum creatinine.
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From the Creator
Why did you develop the Schwartz Equation for GFR? Was there a particular clinical experience or patient encounter that inspired you to create this tool for clinicians?
Estimating GFR takes much less time, and measurement of GFR is very laborious. We used to calculate all the GFRs as fellows at Albert Einstein in the Bronx, New York. We hypothesized that serum creatinine by itself might not be a great marker because growth occurs in children, and with growth is the accretion of muscle mass, which raises serum creatinine. Thus, we tested formulas with a body habitus component as well as serum
What pearls, pitfalls and/or tips do you have for users of the Schwartz Equation for GFR? Do you know of cases when it has been applied, interpreted, or used inappropriately?
The equation must be applied to a stable creatinine
The equation is not useful in children with reduced muscle mass, amputations, cachexia, or those taking creatine supplements.
What recommendations do you have for doctors once they have applied the Schwartz Equation for GFR? Are there any adjustments or updates you would make to the score based on new data or practice changes?
The updated eGFR from 2009 works well, especially with enzymatic serum creatinine. One has to average this with the CKD-EPI eGFR for adolescents and young adults between 18 and 26.
How do you use the Schwartz Equation for GFR in your own clinical practice? Can you give an example of a scenario in which you use it?
I use this regularly to stage my patients. If I am unclear as to whether or not this estimate makes sense, I send out a cystatin C. GFR can be estimated by 70.69 x CysC-0.931. If the two univariate estimates agree within 10%, then that is the eGFR. If there is disagreement, try to see which estimate is likely off. If this is not obvious, you may have to measure GFR in such a patient.
Any other research in the pipeline that you’re particularly excited about?
The Chronic Kidney Disease in Children Study (CKiD) hopes to have a more globally applied eGFR after recruitment of the third cohort. Work will probably begin on this eGFR in a year or so. Meanwhile, the full CKiD eGFR is even more accurate than is the Ht/
About the Creator
George J. Schwartz, MD, is chief of the nephrology division in the department of pediatrics at the University of Rochester Medical Center. He is also an elected member of the American Society for Clinical Investigation. Dr. Schwartz's research interests include acidosis and renal tubular disorders.
To view Dr. George J. Schwartz's publications, visit PubMed
- Juan Kupferman, MD