From the Guidelines
Impaired renal function is indicated by a glomerular filtration rate (GFR) less than 60 mL/min per 1.73 m2, which can be estimated using serum creatinine and standard equations such as the Modification of Diet in Renal Disease study equation or CKD Epidemiology Collaboration equation 1. To determine if there is impaired renal function, several factors should be considered:
- Serum creatinine levels: Higher levels often indicate decreased kidney function, while lower levels are generally not a concern but can occur with muscle wasting or malnutrition.
- GFR: A GFR level less than 60 mL/min per 1.73 m2 represents loss of half or more of the adult level of normal kidney function.
- Urine output: Oliguria may reflect decreased glomerular filtration rate, but changes in urine output may be physiologic.
- Albuminuria: An albumin-to-creatinine ratio greater than 30 mg/g in untimed urine samples is usually considered abnormal.
- Kidney damage: Markers of kidney damage include abnormalities in urine sediment, blood and urine chemistry measurements, and abnormal findings on imaging studies. The diagnosis of impaired renal function is critical, as it can lead to chronic kidney disease (CKD) and increased risk of cardiovascular disease, hypertension, and other complications. The most recent and highest quality study recommends using the estimated GFR and albuminuria to diagnose and classify CKD 1. Some key points to consider:
- CKD is defined as an abnormality of kidney structure or function, present for more than 3 months, with health consequences.
- The prevalence of CKD increases with age, and approximately 17% of persons older than 60 years of age have an estimated GFR less than 60 mL/min per 1.73 m2.
- The guidelines define kidney failure as either a GFR less than 15 mL/min per 1.73 m2 or a need to start kidney replacement therapy. It is essential to evaluate the patient with impaired renal function thoroughly, including a thorough history, physical examination, laboratory analysis, and serologic workups to determine the underlying cause and appropriate treatment. The use of serum creatinine and estimated GFR is recommended for the diagnosis and monitoring of kidney function 2, 3, 4.
From the Research
Impaired Renal Function
Impaired renal function can be indicated by elevated levels of serum creatinine, which may suggest renal failure or other kidney-related issues 5. The following points highlight the relationship between serum creatinine and renal function:
- Elevated serum creatinine levels can be an indicator of renal insufficiency, and earlier referral to a nephrologist may lead to better health care outcomes and lower costs 5.
- Serum creatinine is not an ideal kidney function test, as it depends on muscle mass and has no interindividual normal range, which can lead to overlooked acute kidney injuries with a serum creatinine rise in the 'normal' range 6.
- Patients with elevated serum creatinine and concurrent normal urinalysis may still have underlying kidney diseases, such as acute interstitial nephritis or hypertensive nephrosclerosis, which can be diagnosed through kidney biopsies 7.
Factors Influencing Serum Creatinine
Several factors can influence serum creatinine levels, including:
- Dietary intake, such as excessive creatine intake, which can lead to elevated creatinine levels in otherwise healthy individuals 8.
- Muscle mass, as serum creatinine is dependent on muscle mass and may not accurately reflect kidney function in individuals with low muscle mass 6.
- Age and sex, as the upper normal range of serum creatinine has a higher risk of chronic kidney disease (CKD) development, with different cutoff values for females (0.75 mg/dL) and males (0.78 mg/dL) 9.
Predicting Chronic Kidney Disease
Serum creatinine can be used as a predictor for CKD, even when levels are within the normal range:
- Upper normal serum creatinine concentrations can predict the development of CKD, with a higher incidence of CKD development in individuals with higher quartiles of serum creatinine 9.
- Adding serum creatinine to traditional risk factors for CKD can improve the accuracy of predicting CKD development, with a higher hazard ratio for individuals in the highest quartile of serum creatinine 9.