Creatinine, Blood and Estimated Glomerular Filtration Rate (eGFR)

General

Core Lab Study

Synonym/Acronym:
Cr, SCr

Rationale
To assess kidney function found in acute kidney injury and chronic kidney disease (CKD), related to drug reaction and disease such as diabetes.

This Core Lab Study is included in the basic metabolic panel (BMP), comprehensive metabolic panel (CMP), general health panel, and renal function panel. Panels are used as general health and targeted screens to identify or monitor conditions such as bone disease, diabetes, hypertension, kidney disease, liver disease, or malnutrition. Serum creatinine (SCr) is also ordered with the urine creatinine clearance test.

Patient Preparation
There are no food, fluid, or medication restrictions unless by medical direction. Instruct the patient to refrain from excessive exercise for 8 hr before the test.

Normal Findings
Method: Spectrophotometry for Cr; immunoturbidometry for cystatin C.

Creatinine
AgeConventional UnitsSI Units (Conventional Units × 88.4)
Newborn–11 mo0.17–0.42 mg/dL15–37 mmol/L
1–5 yr0.19–0.49 mg/dL17–43 mmol/L
6–10 yr0.26–0.61 mg/dL23–54 mmol/L
11–14 yr0.35–0.86 mg/dL31–76 mmol/L
15 yr–Adult male0.74–1.35 mg/dL65–119 mmol/L
15 yr–Adult female0.59–1.04 mg/dL52–92 mmol/L
Estimated Glomerular Filtration Rate (eGFR) Many laboratories now report blood Cr and cystatin C values with the corresponding eGFR.
Age Conventional Units
Less than 18 yrNote: 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 yrGreater than or equal to 60 mL/min/body surface area
Greater than 70 yrValues 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.
Cystatin C
Age Conventional Units SI Units (Conventional Units × 74.9)
Adult0.56–1.2 mg/L41.9–89.9 mmol/L
BUN/Cr Ratio 10:1 to 20:1
Values vary among laboratories due to differences in instrumentation.

Critical Findings and Potential Interventions

Adults
Potential critical finding is greater than 7.4 mg/dL (SI: 654.2 micromol/L) (patient not on dialysis).

Children
Potential critical finding is greater than 3.8 mg/dL (SI: 336 micromol/L) (patient not on dialysis).

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.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Chronic renal insufficiency is identified by Cr levels between 1.5 and 3 mg/dL (SI: 132.6 and 265.2 micromol/L); CKD is present at levels greater than 3 mg/dL (SI: 265.2 micromol/L).

Possible interventions may include renal or peritoneal dialysis and organ transplant, but early discovery of the cause of elevated Cr levels might avoid such drastic interventions.

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