Serum cystatin C in pregnant women: reference values, reliable and superior diagnostic accuracy

A simple, endogenous, accurate and minimally invasive marker of glomerular filtration rate (GFR) is much desired in clinical nephrology. Cystatin C fulfills all criteria to be a marker for GFR. For early detection of renal impairment in pregnant women, it is necessary to determine serum cystatin C reference values and the correlation with GFR. The present study was therefore undertaken.

Healthy pregnant women were followed during pregnancy and the postnatal period. Patient demographics included age, height, weight, BMI, parity, total blood count, LFT, urea, creatinine, Na, K, and blood sugar. Serum cystatin C was estimated using particle enhanced nephlo-immunoassay method. All the parameters were recorded at the start of pregnancy and then in each trimester and the postnatal period. Regression analysis correlation coefficient, ANOVA and the Student's t-test were used for analysis using the SPSS statistical package.

A total of 197 pregnant women were included. Mean serum cystatin C for all the women was 0.82 +/- 0.184 mg/l. Serum cystatin C levels were high -0.89 +/- 0.12 mg/l in the first trimester, decreased significantly to 0.651 +/- 0.14 mg/l during the second trimester (p = 0.0000 compared to first trimester), and increased again to 0.82 +/- 0.191 mg/l in the third trimester. After delivery the level rose to 0.94 +/- 0.12 mg/l. A strong correlation was found between serum cystatin C and serum creatinine. A strong negative correlation was found between GFR and cystatin C values in the women (r = -0.546, p = 0.000). A linear relationship was found between GFR and cystatin C levels. A significant increase in the GFR was noted with the progression of pregnancy from 128.06 +/- 29.7 ml/min in the first trimester to 155.2 +/- 29.59 ml/min during second trimester (p = 0.006). A decline in the level of cystatin C exactly parallel to the increase in the GFR was noted with the progression of pregnancy. Interestingly cystatin C was found to have a strong negative correlation with gestational age (r = -0.663, p = 0.000).

Our results indicate that the mean serum cystatin C levels reflect changes in the GFR during the entire pregnancy and also in the postnatal period. Moreover, serum cystatin C levels are independent of age, height, weight, or blood sugar level. Cystatin C can be used for close supervision and early diagnosis of renal impairment in pregnant patients. Cystatin C is a reliable, useful and promising marker of GFR in pregnant women.