Assay

Creatinine

Key Words

CRT, U+E, eGFR

Specimen Collection

Serum (brown), Plasma (orange)

Turnaround time

8hrs

Test indications

Used in the assessment of renal function, as a marker of glomerular filtration rate

Interferences

Recovery may be falsely low when the blood sample is taken while levels of NAC, N-acetyl-p-benzoquinone imine (NAPQI, paracetemol metabolite), and Metamizole (Novaminsulfone, Dipyrone) are present. Venipuncture should be performed prior to the administration of Metamizole. Venipuncture immediately after or during the administration of Metamizole may lead to falsely low results. Icterus in serum/plasma (i.e. elevated bilirubin) can interfere with the assay. For more information please contact the laboratory.

Reference Range

•       <28 days: 27-77umol/L

•       <1 year: 14-34umol/L

•       <3 years: 15-31umol/L

•       <5 years: 23-37umol/L

•       <7 years: 25-42umol/L

•       <9 years: 30-47umol/L

•       <11 years: 29-56umol/L

•       <13 years: 39-60umol/L

•       <15 years: 40-68umol/L

>15 years old:

•       Male: 59-104umol/L

•       Female/pregnant: 45-84umol/L

Analytical error

1.9%

Reference change value

14.8

eGFR

Estimated glomerular filtration rate (eGFR) is reported alongside all creatinine results and estimates glomerular filtration rate based on the patients serum/plasma creatinine, age and sex. It is only an estimation and does not take into account the patient’s body mass, which also affects circulating creatinine concentrations. It is calculated using the following formuli:

Males

  CRT ≤80:        eGFR = 141 x (CRT/(88.4 x 0.9))^-0.411 x (0.993)^Age

CRT >80:        eGFR = 141 x (CRT/(88.4 x 0.9))^-1.209 x (0.993)^Age 

Females:

CRT ≤62:        eGFR = 144 x (CRT/(88.4 x 0.7))^-0.329 x (0.993)^Age

CRT >62:        eGFR = 144 x (CRT/(88.4 x 0.7))^-1.209 x (0.993)^Age 

Please note: the eGFR calculation is not applicable (and as such not reported) in patients who are <18 years old or pregnant

NG203 recommends that the estimation of GFR (eGFR) should not be adjusted by an ethnicity factor. Adjustment to eGFR equations for different ethnicities may not be valid or accurate. Categorisations based on ethnicity do not consider individuals with a diverse range of family or mixed ethnic backgrounds, and differences in eGFR across ethnicities are likely, at least in part to be due to differences in average muscle mass between ethnic groups. Additionally, muscle mass differs between individuals within the same ethnicity and an adjustment based on ethnicity may thereby be inaccurate for some people. 

AKI

The laboratory reports an acute kidney injury (AKI) staging alongside all creatinine results, which is based on the patients current and previous creatinine results, with elevated creatinine results and/or increases in creatinine. There are three stages of AKI (1-3). For more information, please contact the laboratory or the Renal team at Peterborough City Hospital.