Creatinine, Urine, and Creatinine Clearance, Urine

Creatinine, Urine, and Creatinine Clearance, Urine is a topic covered in the Davis's Lab & Diagnostic Tests.

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Synonym/Acronym:
N/A

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
Newborns15–60 mL
Infants
 3–10 days100–300 mL
 11–59 days250–450 mL
 2–12 mo400–500 mL
Children and adolescents
 13 mo–4 yr500–700 mL
 5–7 yr650–1,000 mL
 8–14 yr800–1,400 mL
Adults and older adults800–2,500 mL (average 1,200 mL)
Normally, more urine is produced during the day than at night. With advancing age, the reverse often occurs. The total expected outcome for adults appears to remain the same regardless of age.
Urine Creatinine
AgeConventional UnitsSI Units
Urine Creatinine (Conventional Units × 8.84)
2–3 yr6–22 mg/kg/24 hr53–194 micromol/kg/24 hr
4–18 yr12–30 mg/kg/24 hr106–265 micromol/kg/24 hr
Adult male14–26 mg/kg/24 hr124–230 micromol/kg/24 hr
Adult female11–20 mg/kg/24 hr97–177 micromol/kg/24 hr
Creatinine Clearance
Creatinine Clearance (Conventional Units × 0.0167)
Children70–140 mL/min/1.73 m21.17–2.33 mL/s/1.73 m2
Adult male85–125 mL/min/1.73 m21.42–2.08 mL/s/1.73 m2
Adult female75–115 mL/min/1.73 m21.25–1.92 mL/s/1.73 m2
For each decade after 40 yrDecrease of 6–7 mL/min/1.73 m2Decrease of 0.06–0.07 mL/s/1.73 m2
The 24-hr urine volume is recorded and provided with the results of the creatinine measurement.

Critical Findings and Potential Interventions

  • Degree of impairment:
    • Borderline: 62.5–80 mL/min/1.73 m2 (SI: 1–1.3 mL/s/1.73 m2)
    • Slight: 52–62.5 mL/min/1.73 m2 (SI: 0.9–1 mL/s/1.73 m2)
    • Mild: 42–52 mL/min/1.73 m2 (SI: 0.7–0.9 mL/s/1.73 m2)
    • Moderate: 28–42 mL/min/1.73 m2 (SI: 0.5–0.7 mL/s/1.73 m2)
    • Marked: Less than 28 mL/min/1.73 m2 (SI: Less than 0.5 mL/s/1.73 m2)

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

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