Label Mnemonic: CRT
Epic Lab Code: LAB66
Downtime Form: A-1a General Laboratory Requisition
6240 RCP
Collection Medium:
Plasma Separator Tube 4.5 mL
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
3 mL whole blood in light green top tube or 1 Microtainer® for pediatric patients
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around Time:
1 hour (upon receipt in laboratory)
Reference Range:
Premature 0.3 - 1.0 mg/dL Neonates 0.2 - 0.9 mg/dL 2-12 months 0.2 - 0.4 mg/dL 1-2 years 0.2 - 0.5 mg/dL 3-4 years 0.3 - 0.7 mg/dL 5-6 years 0.3 - 0.7 mg/dL 7-8 years 0.2 - 0.6 mg/dL 9-10 years 0.3 - 0.7 mg/dL 11-12 years 0.3 - 0.9 mg/dL 13-15 years 0.4 - 0.9 mg/dL Males 16 years and older 0.6 - 1.2 mg/dL Females 16 years and older 0.5 - 1.0 mg/dL Note: There are gender-specific ranges only for ages 16 years and older.
Refer to BD Microtainer® Tubes product sheet for detailed sample collection instructions.

Methodology switched from Jaffe method (colorimetric) to enzymatic method on May 10, 2011. This switch also affected estimated glomerular filtration rate (eGFR) calculation.

1. National Kidney Foundation

2. National Kidney Disease Education Program (NKDEP)

3. Lamb EJ, Tomson CRV, Roderick PJ. Estimating kidney function in adults using formulae. Ann Clin Biochem 2005; 42:321-345.

4. Junge W, Wilke B, Balabi A, Klein G. Determination of reference intervals for serum creatinine, creatinine excretion, and creatinine clearance with an enzymatic and modified Jaffe method. Clin Chim Acta 2004; 137-148.
Test Limitations:
Icterus: No significant interference up to an I index of 60 (approximate conjugated and unconjugated bilirubin concentration: 60 mg/dL).

Hemolysis: No significant interference up to an H index of 800.

Lipemia (Intralipid): No significant interference up to an L index of 2000 (approximate triglycerides concentration: 4000 mg/dL). There is poor correlation between turbidity and triglycerides concentration.

Ascorbic acid < 300 mg/L (< 1.7 mmol/L) does not interfere.

Calcium dobesilate (e.g. Dexium) gives falsely low recoveries from 12.0 μmol/L (5 mg/L). Cyanokit (hydroxocobalamin) at therapeutic levels causes significantly higher results.

N-ethylglycine at therapeutic concentrations and DL-proline at concentrations > 1 mmol/L (115 mg/L) give falsely high results. No significant interference up to a creatine level of 4 mmol/L (524 mg/L).

Cephalosporin antibiotics do not affect this test. 2-Phenyl-1,3- indandion (Phenindion) at therapeutic concentrations interferes with the assay.

Hemolyzed samples from neonates, infants or adults with HbF values > 600 mg/dL interfere with the test.

In very rare cases gammopathy, in particular type IgM (Waldenström's macroglobulinemia), may cause unreliable results.

For diagnostic purposes, the results should always be assessed in conjunction with the patient's medical history, clinical examination and other findings.
Enzymatic Colorimetric
CPT Code:
See also:
Creatinine-Other, Body Fluid