CREATININE/CREATINE

Question 1

-formed from creatine and creatine phosphate in muscle and is excreted into the plasma at a constant rate related to muscle mass
-which diffuses into the plasma and is excreted in the urine

Answer 1

Creatinine

Question 2

inversely related to glomerular filtration rate (GFR) and, although an imperfect measure, it is commonly used to assess renal filtration function

Answer 2

Plasma creatinine

Question 3

-synthesized primarily in the liver from arginine, glycine, and methionine
-It is then transported to other tissues, such as muscle, where it is converted to creatine phosphate, which serves as a high-energy source

Answer 3

Creatine

Question 4

loses phosphoric acid

Answer 4

Creatine phosphate

Question 5

loses water to form the cyclic compound

Answer 5

creatine

Question 6

released into the circulation at a relatively constant rate that has been shown to be proportional to an individual’s muscle mass. It is removed from the circulation by glomerular filtration and excreted in the urine

Answer 6

Creatinine

Question 7

used to determine the sufficiency of kidney function, to determine the severity of kidney damage, and to monitor the progression of kidney disease

Answer 7

Measurement of creatinine concentration

Question 8

function of relative muscle mass, the rate of creatine turnover, and renal function. The amount of creatinine in the bloodstream is reasonably stable, although the protein content of the diet does influence the plasma concentration

Answer 8

Plasma creatinine concentration

Question 9

may be expressed as a ratio to creatinine quantity rather than as mass excreted per day

Answer 9

Urinary constituents

Question 10

measure of the amount of creatinine eliminated from the blood by the kidneys

Answer 10

Creatinine clearance (CrCl)

Question 11

used to gauge renal function

Answer 11

GFR

Question 12

The observed relationship between plasma creatinine and GFR and relatively constant plasma creatinine concentrations should make the analyte a good endogenous filtration marker. However, measurement of plasma creatinine does not provide sufficient sensitivity for the detection of

Answer 12

mild renal dysfunction

Question 13

used in combination with other variables in one of several empirically determined equations provides a better assessment of renal disease, in part because the equations estimate GFR, not CrCl.

Answer 13

Measured creatinine concentration

Question 14

Clinical laboratories have been strongly encouraged to report an estimated GFR when serum creatinine is ordered as a means to increase identification of kidney disease and improve patient care.35 Initially, the abbreviated ___________________________ (MDRD) equation was advocated

Answer 14

Modification of Diet in Renal Disease

Question 15

The equation includes four variables and makes the assumption that all filtered creatinine is excreted

Answer 15

serum creatinine concentration, age, gender (sex), and ethnicity

Question 16

most useful when serum creatinine results are produced in an assay that has been calibrated to be traceable to an IDMS method

Answer 16

MDRD equation

Question 17

When serum creatinine is measured using an IDMS-traceable method, the MDRD equation for_________________________________where Scr is serum (plasma) creatinine concentration in mg/dL and age is in years

Answer 17

estimated glomerular filtration rate (eGFR)

Question 18

published an equation developed using results from healthy adults and adults with chronic kidney disease

Answer 18

The Chronic Kidney Disease Epidemiology (CKD-EPI) Collaboration

Question 19

used to report higher values (>60 mL/min/1.73 m2) for adults 18 years and older

Answer 19

CKDEPI equation

Question 20

developed to calculate eGFR in the pediatric population

Answer 20

modified Schwartz equation

Question 21

-first described in 1886
-methods most frequently used to measure creatinine
-In this reaction, creatinine reacts with picric acid in alkaline solution to form a red-orange chromogen

Answer 21

Jaffe reaction

Question 22

The reaction was adopted for the measurement of blood creatinine by

Answer 22

Folin and Wu in 1919

Question 23

The reaction is nonspecific and subject to positive interference by a large number of compounds, including

Answer 23

acetoacetate, acetone, ascorbate, glucose, and pyruvate

Question 24

-More accurate results are obtained when creatinine in a protein-free filtrate is adsorbed onto
-then eluted and reacted with alkaline picrate. This method is time consuming and not readily automated; it is not routinely used

Answer 24

Fuller’s earth (aluminum magnesium silicate) or Lloyd’s reagent (sodium aluminum silicate)

Question 25

Two approaches have been used to increase the specificity of assay methods for creatinine:

Answer 25

kinetic Jaffe method and reaction with various enzymes

Question 26

serum is mixed with alkaline picrate and the rate of change in absorbance is measured.45 Although this method eliminates some of the nonspecific reactants, it is subject to interference by α-keto acids and cephalosporins

Answer 26

kinetic Jaffe method

Question 27

may cause a negative bias, probably a result of their destruction in the strong base used

Answer 27

Bilirubin and hemoglobin

Question 28

The kinetic Jaffe method is used routinely despite these problems because it is

Answer 28

inexpensive, rapid, and easy to perform

Question 29

-In an effort to enhance the specificity of the Jaffe reaction, several coupled enzymatic methods have been developed. The method using
-was adapted for use on a dry slide analyzer

Answer 29

creatininase (creatinine amidohydrolase, EC 3.5.2.10), creatinase (creatine amidinohydrolase, EC 3.5.3.3), sarcosine oxidase (EC 1.5.3.1), and peroxidase (EC 1.11.1.7)

Question 30

Assays used on automated analyzers are designated as “_______” (calibrated) to an IDMS method

Answer 30

traceable

Question 31

Creatinine may be measured in

Answer 31

plasma, serum, or urine

Question 32

should be avoided, particularly if a Jaffe method is used

Answer 32

Hemolyzed and icteric samples

Question 33

may produce erroneous results in some methods

Answer 33

Lipemic samples

Question 34

is not required, although high-protein ingestion may transiently elevate serum concentrations

Answer 34

fasting sample

Question 35

should be refrigerated after collection or frozen if longer storage than 4 days is required

Answer 35

Urine

Question 36

may increase creatinine concentration measured by the Jaffe reaction, especially at temperatures above 30°C. This interference is significantly decreased when kinetic measurement is applied.

Answer 36

Ascorbate, glucose, α-keto acids, and uric acid

Question 37

causes a negative bias in both Jaffe and enzymatic methods

Answer 37

Bilirubin

Question 38

will interfere in enzymatic methods that use peroxidase as a reagent

Answer 38

Ascorbate

Question 39

may have falsely elevated results when the Jaffe reaction is used. Other drugs have been shown to increase creatinine results.

Answer 39

Patients taking cephalosporin antibiotics

Question 40

in particular, is known to affect both enzymatic and Jaffe methods

Answer 40

Dopamine

Question 41

causes a positive bias in some enzymatic methods

Answer 41

Lidocaine