The NKDEP recommends using the estimating equation for GFR based on serum Because the relationship between serum creatinine and GFR is difficult to. 5) What is the difference between creatinine clearance and GFR? 6) What is 46 ) What is the relationship between stages of CKD and complications of CKD?. The relationship between estimated GFR and the four factors is shown graphically and discussed. An eGFR/creatinine conversion table for individual patients.
Serum Creatinine and Glomerular Filtration Rate: Perception and Reality
The physics is confirmed by Spanaus et al. Further exploration of the discrepancy between our perception of serum creatinine and the conclusions of Spanaus et al. Publications promoting new serum biomarkers of GFR have tended to use ROC curve analysis to demonstrate better, usually only marginally, diagnostic performance; however, diagnosis represents only one of the clinical applications of measuring serum creatinine.
A clinically crucial situation in which creatinine is considered both diagnostically sensitive and reliable is the monitoring of graft function after renal transplantation, for which alterations in the dosing of immunosuppressive drugs are based on small changes in the serum creatinine concentration, usually within the reference interval.
The explanation for the contradiction to our perception lies in an understanding of biological variation, a fundamental concept in clinical chemistry.
The implicit conclusions are that applying a reference interval for serum creatinine is inappropriate, thereby resolving the apparent incongruity of the Shemesh data 12and that longitudinal monitoring of serum creatinine in any individual will ensure early detection of GFR decline and incipient renal disease. This example of truly personalized medicine in which reference intervals do not apply is applicable only when the biological variation of the analyte is low and analytical methods with the appropriate imprecision are available.
Unfortunately, this simple truth is not universally appreciated. The true clinical value of serum creatinine is its diagnostic sensitivity in detecting small changes in GFR.
Serum Creatinine and Glomerular Filtration Rate: Perception and Reality | Clinical Chemistry
Consequently, the use of cystatin C to monitor renal function in an individual, particularly in the early stages of kidney disease or after transplantation, is not valid. It can be used to evaluate the posttransplantation GFR 16 but not the small changes that will determine adjustments to immunosuppressive therapy. Serum creatinine is not a perfect biomarker of GFR. Tubular secretion, an altered production rate, and analytical specificity mean that it is not applicable in all clinical situations, and interpretation often remains an art.
The professional perception that serum creatinine is an insensitive biomarker of early changes in GFR is totally incorrect. The data presented by Spanaus et al. The reality is that serum creatinine is still a very good measure of GFR and is by far the most sensitive serum biomarker for detecting small GFR changes in an individual.
All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: No authors declared any potential conflicts of interest. The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.
Two clinical lectures on albuminuria. The vagaries of renal disease. Br Med J ;1: The original MDRD equation was developed using creatinine results measured by a routine method that had a small positive bias compared to an IDMS reference measurement procedure.
Since many routine methods have a similar bias, this conventional calibration equation is recommended for creatinine results from methods that have not been calibrated to be traceable to IDMS. It is recommended to report two values for the estimated GFR, one value if the patient is African American and another value if the patient is not African American.
The reason for this recommendation is that race can be difficult to represent reliably in electronic medical records and it is difficult, even if the race is noted, to know if the patient is of a mixed ethnic background. If the calculated GFR value is less than or equal to 60, it is recommended to report the value rounded to a whole number e. The reason not to report numeric values greater than 60 is because the impact of variability in the creatinine measurement has a progressively greater impact on the variability of the calculated GFR value as the creatinine value becomes smaller corresponding to more normal renal function, and the accuracy of the estimated GFR is poorer at higher GFRs .
Laboratories need to communicate to clinical providers and to pharmacists the clinical issues associated with a creatinine method that is calibrated to be traceable to IDMS. The critical clinical issues are the change in reference range, and the impact on using creatinine and calculated GFR to adjust dosage of nephrotoxic drugs.
The algorithms used to adjust drug dosages are usually based on the Cockcroft-Gault equation or the absolute creatinine value. Because the product labeling for drugs is based on one of these approaches, pharmacists and providers are obliged to use those algorithms.
Reporting calculated GFR from serum creatinine
Consequently, the laboratory must provide information on the magnitude of difference between an IDMS-traceable creatinine result and a result by the former method used by the laboratory.
There are two principal approaches to establish traceability to a RMP. One approach is to measure native clinical samples, using the routine method and using the RMP.
The product calibrator s for the routine method is then value assigned to produce results for the native clinical samples that are equivalent to those from the RMP. The other approach to establish the values for the routine method product calibrator s is to use a reference material that is commutable with the native clinical samples between the RMP and the routine method, and which has its value assigned by a RMP.
Reporting calculated GFR from serum creatinine
IVD manufacturers may also need to address imprecision and non-specificity of creatinine methods. IVD manufacturers should provide information to customers regarding the relationship between results from a creatinine method calibrated to be traceable to IDMS and previous conventionally calibrated methods.
This is essential information that the laboratory needs to make available to clinical providers and to pharmacists.
In addition, IVD manufacturers should provide educational information to laboratories to assist them in reporting calculated GFR and in the transition from conventionally calibrated to IDMS-calibrated routine methods. IVD manufacturers should communicate with external quality assurance proficiency testing programs to ensure that laboratories participating in those programs are graded appropriately during the transition period from conventionally calibrated to IDMS-calibrated routine methods.
External quality assurance proficiency testing providers should ensure that participants are appropriately graded when there may be a bimodal distribution of results as some laboratories report results using reagent and calibrator inventory that has been conventionally calibrated, while others report results using newer inventory that has IDMS-traceable calibration.
Prevalence of chronic kidney disease and decreased kidney function in the adult US population: Am J Kidney Dis ; Kidney Disease Outcome Quality Initiative.
Performance of the modification of diet in renal disease and Cockcroft-Gault equations in the estimation of GFR in health and in chronic kidney disease. J Am Soc Nephrol ;