Due to the inverse relationship between serum creatinine and GFR, a small change in serum creatinine from to mg/dL will represent a relatively large . That's because the level of creatinine in your blood is affected by your age, race, gender, and body size. GFR is a routine lab that can be found on your blood work report. Yes, another important test to check kidney function is a urine test. There is a difference between looking at creatinine in your. For practical reasons, the blood test estimation method for GFR is used far more often than the hour urine collection test for creatinine.
Radiolabelled methods for measuring GFR are accurate but not practical and can be used only on a very limited scale while the traditional methods require timed urine collection with its drawback of inaccuracy, cumbersomeness and inconvenience for the patients.
Serum Creatinine and Glomerular Filtration Rate: Perception and Reality | Clinical Chemistry
It is the implementation of these equations particularly the MDRD that has raised the medical awareness in the diagnosis and management of CKD and its adoption by many guidelines in North America and Europe. The impact and pitfalls of each of these equations in the screening, diagnosis and management of patients with CKD are presented and discussed in this review.
The increasing prevalence of many chronic diseases particularly diabetes mellitus, hypertension, cardiovascular and renal diseases together with the increasing medical care and its impact on improving life expectancy have all centered on the importance of organs functions assessment including most importantly renal function.
Chronic kidney disease CKD is also a significant risk factor for vascular disease and early cardiovascular mortality as well as progression of kidney disease. Accordingly, CKD is classified into five stages: NICE guidance also recommended the use of suffix p to denote the presence of proteinuria when staging CKD, using random urine albumin-to-creatinine ratio in preference to protein-to-creatinine ratio.
Screening populations at risk of developing CKD is considered now to be a major challenge in the management of patients with underlying chronic diseases and is of much interest particularly to Clinicians including Nephrologists, Diabetologists, and General Practitioners.
Formula- Based Calculation of eGFR The approach of screening for any underling kidney damage has been facilitated and become routinely available with the advent of calculating the estimated GFR eGFR from serum creatinine based on formulae that take into consideration a number of patient's characteristics. By this approach, the result of serum creatinine is converted into physiological units of GFR.
Despite the ongoing analytical improvement in the techniques of creatinine measurement, however still it is suffering from limited sensitivity and specificity, analytical interferences and standardization problems. Untilthere were more than 25 of such formulae with Cockraft and Gault formula 11 appears to be the most attractive and validated one in adults where by: Ina great change in the utilization of creatinine- based calculation of GFR was launched in practice by Levey et al 13 who validated a new equation for calculating eGFR based on serum creatinine, age, sex and ethnicity as well as urea and albumin using 6- variables Modification of Diet in Renal Disease 6-v MDRD equation.
The inclusion of urea and albumin was a limitation for the added cost and analytical variation. Recognizing this, in Levey et al 14 subsequently published a 4-variables 4-v MDRD equation that does not require albumin and urea with no impact on accuracy, whereby: This approach started to gain a core role as a suitable measure of kidney function that was quickly understood by almost all physicians. This was recommended in order to prevent people developing kidney disease in the first instance or to slow down the progression of kidney damage and minimize cardiovascular risk when a diagnosis has been made.
This recommended system of reporting is mostly followed in USA and Canada.
Reporting eGFR has to be interpreted with caution in acute renal failure, pregnancy, oedematous states, muscle wasting disorders, amputees, paraplegics, morbid obese, and malnourished people. MDRD can be used for drug dosage adjustment instead of creatinine clearance. Exceptions include potentially toxic drugs with small safety margin and patients at extreme of age, 20 a recommendation that was supported by Stenvens et al. Whilst these estimates may be used in certain settings, however routine reporting of eGFR in children by laboratories may not be easily recommended.
Currently, there is no doubt that eGFR. MDRD is considered to be an integral test in renal function assessment and has growing role in alerting the clinicians about the renal function status.
Reporting calculated GFR from serum creatinine
The interpretation of eGFR gained wise approach by requesters in that the numerical value of the result may reflect the proportional function of the intact functioning nephrons. This is contrary to serum creatinine whose reference range varies greatly depending on age, sex, gender and muscle mass, making many interpreters unaware and inexperienced in its interpretation particularly when the level is slightly elevated, at which level it really reflects significant renal impairment.
It has been observed particularly in the last few years following the introduction of eGFR reporting that there is an increase in the number of people in the Primary Care recognized to have CKD as well as increase in patient's referral to nephrologists. Therefore, the need for more efficient and accurate screening tests was addressed as the currently used eGFR. MDRD method is not without dubious value.
The equation based eGFR does not consider in depth the expected normal age and gender decline in GFR which may result in many elderly subjects particularly those not at risk to be labeled as having CKD.
Serum Creatinine and Glomerular Filtration Rate: Perception and Reality
Whether CKD should be considered or staged based on modest decline in eGFR in elderly subjects without other risk factors may be debatable. Hence targeted screening of at risk individuals will be more clinically and cost-effective approach, a message that could be easily transmitted through public health programs.
The equations are as follows: Although statistically significant at all age groups the difference diminished with age. Other Markers of Chronic Kidney Disease Of additional importance in this regard is the role of the presence or absence of albuminuria in the stratification of all stages of CKD, including diagnosing, staging and monitoring as has been recommended in the many guidelines.
The near future may show an analytical improvement in creatinine measurement with its impact in improving the sensitivity of the assay and hence eGFR reporting. Also, implementing and evaluating other markers of renal function such as measurement of serum Cystatin C and other markers of kidney injury may add to the diagnostic and management role of renal function testing in renal medicine. Despite its limitations, the implementation of eGFR reporting especially in high-risk patients has significantly contributed in the early recognition of CKD that allows the provision of appropriate therapy and so alerting the clinicians for the impact of chronic diseases on kidney function.
There are many equations for calculating eGFR from serum creatinine in adults without the need for urine collection. The need of Cockcroft and Gault equation for body weight has limited its routine application in laboratory practice.
However, the ease of MDRD equation which does not require body weight for eGFR calculation has contributed in its rapid implementation and acceptance in clinical medicine with recommendation towards its routine reporting together with serum creatinine as a renal function profile.
Following the introduction of eGFR reporting, there has been a paradigm shift from CKD being viewed as secondary care condition to being primary care priority with an increase in the number of people in the primary care recognized to have CKD, in the prevalence of CKD and in patient's referral to nephrologists.
However, the equation still has its own controversy particularly in under-estimating GFR at low-normal level of serum creatinine, in diagnosing stage CKD, in women, and in the elderly. It is also important to ensure that all health care professionals, both generalists and specialists, understand the importance of the early diagnosis of kidney disease. Physicians should be made especially aware that older patients and those with diabetes, hypertension, or cardiovascular disease should be systematically screened for the presence of CKD, a message that could be easily transmitted through public health programs.
Recently measurement of albuminuria has been recommended in many guidelines, as both reduced eGFR and albuminuria are strong predictors for cardiovascular events and progression of renal disease.
Finally, continuous efforts should be considered in the development and validation of the renal function tests including analytical improvement in creatinine measurement with its impact in improving the assay sensitivity and hence eGFR reporting. Acknowledgements The authors reported no conflict of interest and no funding was received on this work.
Chronic Kidney Disease Prognosis Consortium Lower estimated glomerular filtration rate and higher albuminuria are associated with mortality and end-stage renal disease. A collaborative meta-analysis of kidney disease population cohorts.
Am J Kidney Dis Feb;39 2 Suppl 1: Early identification and management of chronic kidney disease in adults in primary and secondary care. Over the last 40 years, the clinical importance of serum creatinine measurements in diagnosing renal disease and then enabling accurate monitoring of disease progression cannot be over emphasized.
The development of formulae for estimating GFR 7 and disease staging 8 based on serum creatinine reiterate the continuing importance of this biomarker. Why, then, is the professional perception of serum creatinine so negative?
Consequently, drugs that inhibit the tubular secretion of creatinine [e. Similar problems of interpretation arise from changes in the creatinine-production rate, with observed increases in response to therapeutics [e.
Reporting calculated GFR from serum creatinine
The vital evidence underlying our negative perception of serum creatinine, however, is the data reported by Shemesh et al. The pressure to change to new serum biomarkers of GFR becomes ever more vocal. Formal GFR was measured by iohexol clearance.
The authors provide a detailed discussion of the limitations of their study, but their conclusions that the 3 biomarkers are equivalent, both in terms of diagnostic performance—even for minor degrees of deterioration of renal function—and in terms of risk prediction for progression, should help to improve our perception of serum creatinine.
Any serum biomarker of GFR must obey the laws of physics: As the GFR declines, the serum concentration should increase. The fact that the relationship between serum concentration and GFR is a reciprocal function explains how the relatively small changes in concentration that occur in the early stages of renal function decline are followed by an accelerating increase. Consequently, for decades nephrologists in clinical practice have monitored the rate of progression of renal disease in patients by simply plotting the reciprocal of the serum creatinine concentration against time.
This reciprocal function is not unique to creatinine but is true for any biomarker of GFR. 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.