Endogenous creatinine clearance during pregnancy. II. Variations in normal standards based on methodology

Area of Science:

• Nephrology
• Clinical Chemistry
• Obstetrics

Background:

• Endogenous creatinine clearance (ECC) is a key indicator of renal function.
• Accurate creatinine measurement is crucial for assessing ECC, especially during pregnancy.
• Different analytical methods for creatinine may yield varying results.

Purpose of the Study:

• To compare ECC values derived from creatinine levels measured by an autoanalyzer versus the modified Jaffe reaction.
• To evaluate the impact of different creatinine assays on ECC assessment across gestation.
• To determine if method-specific differences in serum creatinine persist in the nonpregnant state.

Main Methods:

• A comparative study involving 108 healthy pregnant women at various gestational stages.
• Measurement of serum creatinine using an autoanalyzer and the modified Jaffe reaction with Lloyd's reagent.
• Calculation and comparison of endogenous creatinine clearance (ECC) based on both methods.

Main Results:

• Mean ECC was significantly lower with the autoanalyzer method compared to the modified Jaffe reaction, except between 39-41 weeks of gestation.
• Autoanalyzer-derived ECC remained consistent throughout pregnancy due to stable serum creatinine levels.
• The discrepancy in serum creatinine levels between the two methods observed during pregnancy was not present in nonpregnant individuals.

Conclusions:

• The choice of creatinine assay significantly impacts ECC estimations in pregnant women.
• Autoanalyzer-based creatinine measurements provide a more stable ECC assessment during pregnancy.
• Methodological differences in creatinine assays are specific to the pregnant state and resolve postpartum.