Urinary creatinine instability falsely increases the deoxypyridinoline/creatinine quotient.
BACKGROUND
The concentration of urinary deoxypyridinoline crosslinks (Dpd) (as in line 17)-normalized with respect to the urinary creatinine concentration is used as a biochemical marker of pathological bone resorption.


METHODS
The effect of various storage conditions on the stability of Dpd/creatinine in urine specimens was examined in a sample of 14 individuals without aseptic endoprosthetic loosening (control) and 14 patients with aseptic endoprosthetic loosening (AEL).


RESULTS
In the control group, values of Dpd/creatinine measured after 1 day of storage at -20 degrees C were significantly greater (p < 0.005) than values measured in fresh urine specimens. In the AEL group, increases in urinary Dpd/creatinine values were less pronounced (NS to p < 0.05). Increases in Dpd/creatinine were primarily the mathematical consequence of significant decreases in urinary creatinine concentration in the control group (p < 0.0001) and the AEL group (p < 0.05, after at least 7 days of storage). The decrease in urinary creatinine concentration appears to reach a plateau--between 75% and 80% of the original value--after approximately 10 days of storage.


CONCLUSIONS
To prevent falsely increased Dpd/creatinine quotients, we suggest that urinary creatinine should be measured exclusively in fresh urine specimens or consistently in specimens stored for at least 14 days at -20 or -80 degrees C.
Orthopädische Universitätklinik, Klinikum der RWTH Aachen, Pauwelsstr 30, 52074 Aachen, Germany. U.Schneider@post.rwth-aachen.de
Ulrich
U
Schneider
Edward A
EA
Schober
Nikolaus A
NA
Streich
Steffen J
SJ
Breusch
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000596:Amino Acids / Q000652:urine*; D016477:Artifacts; D015415:Biomarkers / Q000652:urine; D001862:Bone Resorption / Q000175:diagnosis* / Q000652:urine*; D016022:Case-Control Studies; D003404:Creatinine / Q000652:urine*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013048:Specimen Handling / Q000379:methods*; D013696:Temperature; D013997:Time Factors
D000596:Amino Acids; D015415:Biomarkers; C036020:deoxypyridinoline; D003404:Creatinine