Synonym/Acronym
eGFR, CrCl
Rationale
To assess and monitor kidney function related to acute kidney injury or chronic kidney disease.
Patient Preparation
There are no fluid or medication restrictions unless by medical direction. Instruct the patient to refrain from eating meat during the test and to refrain from excessive exercise for 8 hr before the test. Protocols may vary among facilities. Usually, a 24-hr urine collection is ordered. As appropriate, provide the required urine collection container and specimen collection instructions.
Normal Findings
Method: Spectrophotometry.
| Normal Urine Volume per 24 hr | |||
| These ranges are very general averages and were not calculated on the basis of normal average body weights. Literature shows that expected urinary output can be estimated by a formula in which the expected output is as follows:
Infants: 1–2 mL/kg/hr Children and adolescents: 0.5–1 mL/kg/hr Adults and older adults: 1 mL/kg/hr | |||
| Newborns | 15–60 mL | ||
| Infants | |||
| 3–10 d | 100–300 mL | ||
| 11–59 d | 250–450 mL | ||
| 2–12 mo | 400–500 mL | ||
| Children and adolescents | |||
| 13 mo–4 yr | 500–700 mL | ||
| 5–7 yr | 650–1,000 mL | ||
| 8–14 yr | 800–1,400 mL | ||
| Adults and older adults | 800–2,500 mL (average 1,200 mL) | ||
| Timed Urine Creatinine | ||
|---|---|---|
| Age | Conventional Units | SI Units = (Conventional Units × 0.00884) |
| 3–8 yr | 140–700 mg/24 hr | 1–6 mmol/d |
| 9–12 yr | 300–1,300 mg/24 hr | 3–12 mmol/d |
| 13–17 yr | ||
| Male | 500–2,300 mg/24 hr | 4–20 mmol/d |
| Female | 400–1,600 mg/24 hr | 3.5–14 mmol/d |
| 18–50 yr | ||
| Male | 1,000–2,500 mg/24 hr | 8.8–22 mmol/d |
| Female | 700–1,600 mg/24 hr | 6.2–14 mmol/d |
| 51–80 yr | ||
| Male | 800–2,100 mg/24 hr | 7–18.6 mmol/d |
| Female | 500–1,400 mg/24 hr | 4–12.4 mmol/d |
| 81 yr and older | ||
| Male | 600–2,000 mg/24 hr | 5–17.7 mmol/d |
| Female | 400–1,300 mg/24 hr | 3.5–12 mmol/d |
| Random Urine Creatinine | ||
| Note: Laboratories may not report an established normal range | Conventional Units | SI Units = (Conventional Units × 0.0884) |
| Adult male | 20–320 mg/dL | 1.77–28.3 mmol/L |
| Adult female | 20–275 mg/dL | 1.77–24.3 mmol/L |
| Creatinine Clearance | SI Units = (Conventional Units × 0.0167) | |
| Children | 70–140 mL/min/ 1.73 m2 | 1.17–2.33 mL/sec/ 1.73 m2 |
| Adult male | 85–125 mL/min/ 1.73 m2 | 1.42–2.09 mL/sec/ 1.73 m2 |
| Adult female | 75–115 mL/min/ 1.73 m2 | 1.25–1.92 mL/sec/ 1.73 m2 |
| For each decade after 40 yr | Decrease of 6–7 mL/min/1.73 m2 | Decrease of 0.06–0.07 mL/sec/1.73 m2 |
The 24-hr urine volume is recorded and provided with the results of the creatinine measurement.
| Estimated Glomerular Filtration Rate (eGFR) Many laboratories now report eGFR with creatinine clearance. | |||
| Age | Conventional Units | ||
| Less than 18 yr | Note: The eGFR equation generally recommended for individuals under 18 yr of age is the Bedside Schwartz formula and is based on Cr levels and height in centimeters. | ||
| 18–70 yr | Greater than or equal to 60 mL/min/body surface area | ||
| Greater than 70 yr | Values in older adults remain relatively stable, after a period of decline related to loss of muscle mass during the transition from adult to older adult. | ||
(Study type: Urine from an unpreserved random or timed specimen collected in a clean plastic collection container; related body system: .)
Chronic kidney disease (CKD) is a significant health concern worldwide. International research has been undertaken to evaluate the risk factors common to cardiovascular disease, diabetes, and hypertension; these three diseases are all associated with CKD. Albuminuria (formerly referred to as microalbuminuria), which can result from increased glomerular permeability to proteins, is considered an independent risk factor predictive of kidney or cardiovascular disease.
Creatinine is the end product of creatine metabolism. Creatine resides almost exclusively in skeletal muscle, where it participates in energy-requiring metabolic reactions. In these processes, creatine is irreversibly converted to Cr, which then circulates to the kidneys and is excreted into the urine at a relatively consistent rate. A consistent rate of excretion is the reason urine creatinine measurements have been used to evaluate kidney health for many years. The amount of Cr generated in an individual is proportional to the mass of skeletal muscle present and remains fairly constant, unless there is massive muscle damage resulting from crushing injury or degenerative muscle disease. Cr values normally decrease with age owing to diminishing muscle mass. Conditions involving degenerative muscle wasting or massive muscle trauma from a crushing injury will also result in decreased Cr levels.
For additional information regarding other significant markers of kidney health, refer to the study titled “Albumin, Urine and Albumin/Creatinine Ratio (ACR)” and “Creatinine, Blood and Estimated Glomerular Filtration Rate (eGFR).”
Urine Creatinine (Timed)
Measurement of urine creatinine is an effective indicator of kidney function and is ordered with almost every timed, quantitative urine study (e.g., 5-hydroxyindoleacetic acid, calcium, drug screen, lead, potassium, sodium, protein).
Timed urine creatinine collections are used to validate the completeness of a 24-hr collection in patients with normal kidney function. For example, if a 24-hr urine sodium is requested, two tests will be performed: a urine sodium and a urine creatinine. The measured urine creatinine value is compared to the established 24-hr urine creatinine normal range. If the urine creatinine value falls within the 24-hr urine creatinine reference range, the collection is validated as complete. Circumstances that may indicate an invalid collection include incomplete collection (e.g., not adding all voided urine into the collection container) or inaccurate recording of urine volume or collection times.
The same concept of validation applies to urine drug screen samples where the patient sample findings might not match up to expected standard results (e.g., the drug levels are very low and the creatinine is abnormally low—the specimen may be rejected for analysis possibly due to dilution of the patient sample with water in an effort to falsely decrease the drug test measurements).
Urine Creatinine (Random)
While timed urine collections are preferred, random or spot urine collections are often used for a quick screen (e.g., electrolytes, albumin).
Creatinine clearance
The creatinine clearance test measures a blood sample and a urine sample to determine the rate at which the kidneys are clearing creatinine from the blood; this reflects the glomerular filtration rate (GFR) and is based on an estimate of body surface. eGFR formulas are now routinely used to evaluate kidney function; their use has become more common than other tests that reflect GFR, such as the creatinine clearance test. The CrCl is more complicated and time consuming to perform; it has become impractical for routine use given the near instantaneous availability of mathematically derived algorithms. Many laboratories include the eGFR with the results of the creatinine clearance.
eGFR
There are multiple formulas in use for calculation of the eGFR. Either Cr or cystatin may be used. The most common formulas use SCr value, age, and correction factors for gender and race. In September 2021, the National Kidney Foundation and American Society of Nephrology joint task force released its final report, which outlines a race-free approach for the diagnosis of kidney disease and recommends the use of the CKD-EPI Cr calculation (2021) for eGFR. The recommendation was endorsed by the U.S. Pathology and Laboratory Society Leadership in February 2022. Laboratories have begun to transition to race-free eGFR calculations. For additional information regarding eGFR and eGFR for pregnant females and children under 18 yr of age, refer to the study titled “Creatinine, Blood, and Estimated Glomerular Filtration Rate (eGFR).”
Recommendations for measuring and reporting creatinine values and eGFR (formulas are available that use Cr and/or cystatin to calculate eGFR):
Other Considerations
Increased In
Decreased In
Conditions that decrease GFR, impair kidney function, or reduce renal blood flow will decrease renal excretion of creatinine.
eGFR
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
Potential Nursing Actions
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
Clinical Judgement
Follow-Up Evaluation and Desired Outcomes