Commutability Study Results |
View the Commutability Study Results for NIST SRM 967 and CAP LN24. |
Creatinine Standardization Recommendations
Clinical laboratories are crucial partners in the successful
implementation of the Creatinine Standardization Program. For clinical
laboratories, the following steps are necessary:
- Continue using the Original
Modification of Diet in Renal Disease (MDRD) Study equation for routine
methods that have not been calibrated to be
traceable to IDMS. It is appropriate to use this equation because most
methods in this category will produce creatinine results that have a
bias similar to that of the method used in developing the Original MDRD
Study equation. Contact the reagent and/or calibrator manufacturer with
questions about the traceability of the calibration for the method used
in your laboratory.
- Coordinate with your creatinine
method provider to ensure immediate use of the IDMS-traceable MDRD
Study equation for estimating GFR once your lab begins using a
creatinine method that has its calibration traceable to isotope
dilution mass spectrometry (IDMS). During the transition to
IDMS-traceable calibration, methods that produce results that have
acceptable bias [as defined in Clinical
Chemistry
2006;52(1):5-18] when compared to an IDMS-traceable method
also should use the IDMS-traceable MDRD Study equation.
- Communicate the following to health
care providers, including pharmacists, when using a serum creatinine
method that has its calibration traceable to an IDMS reference method:
- Serum creatinine reference
intervals will change, depending on the method. Provide the reference
interval appropriate for the method.
- All creatinine-based equations,
other than the IDMS-traceable MDRD Study equation, used to estimate
kidney function, such as Cockcroft-Gault, Schwartz, or
Counahan-Barratt, will give values that, in most cases, are higher than
the values obtained using traditionally calibrated creatinine methods.
This change in calibration will affect interpretive criteria and drug
dosage adjustments based on these estimates of kidney function.
Guidance for using the Schwartz equation with creatinine measured by
methods that have calibration traceable to IDMS is available in the GFR Calculators
section.
- Provide the relationship
(including mathematical conversion factors, equations, or functions)
between creatinine results when measured with a method that has
IDMS-traceable calibration compared to the results obtained using a
method with traditional calibration with emphasis on the 0.5 to 2.5
mg/dL (45 to 220 µmol/L) range that is most important for
drug dose adjustments. This information will ensure that any of the
pharmacy drug dosing approaches can adjust IDMS-traceable creatinine
values for use with appropriate legacy dosing reference tables and
algorithms (such as serum creatinine value; GFR or creatinine clearance
based on estimating equations other than the MDRD Study equation. Read
NKDEP’s recommendations for pharmacists and
authorized drug prescribers.
- Creatinine clearance calculated
from serum and urine creatinine may increase depending on how the
measurements for serum and urine are calilbrated. Reference interval
and interpretive criteria for creatinine clearance may change.
- For assessing kidney function
in most patients, an estimated GFR (eGFR) using the MDRD Study equation
is more accurate than a creatinine clearance calculated from serum and
urine measurements. Therefore, NKDEP recommends against performing a
measured creatinine clearance procedure for adults except when the
patient's basal creatinine production is abnormal. This may be the case
with patients of extreme body size or muscle mass (e.g., obese,
severely malnourished, amputees, paraplegics or other muscle-wasting
diseases) or with unusual dietary intake (e.g., vegetarian, creatine
supplements).
- Creatinine measurements at the
low values usually observed in pediatric patients have greater
measurement variability than for values seen in adults. Estimates of
kidney function based on these values also will have greater
variability than for adults.
- Report Proficiency Testing and External
Quality Assessment (PT/EQA) results for serum and urine creatinine
using the correct instrument/method peer group for IDMS-traceable
calibration. IVD manufacturers and NKDEP are cooperating to inform PT/EQA providers of the participant grading issues during the transition to standardized creatinine methods. (See NKDEP’s recommendations
for PT/EQA providers.)
- Monitor calibration performance
of routine methods that have calibration traceable to an IDMS reference
method through use of the College of American Pathologists' LN24 Survey
(commutability
validated), or comparable EQA with commutable samples and
IDMS target values.
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