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  • Title: Development of normal reference intervals for renal function in pregnancy: a secondary analysis of clinical trial data.
    Author: Legoabe Z, Sebitloane M, Lombard C, Naidoo M, Gray G, Moodley D.
    Journal: J Obstet Gynaecol; 2024 Dec; 44(1):2361445. PubMed ID: 38832538.
    Abstract:
    BACKGROUND: Due to its potential nephrotoxicity, screening for pre-existing renal function disorders has become a routine clinical assessment for initiating Tenofovir diphosphate fumarate (TDF)-containing antiretroviral treatment (ART) or pre-exposure prophylaxis (PrEP) in pregnant and non-pregnant adults. We aimed to establish reference values for commonly used markers of renal function in healthy pregnant women of African origin. METHODS: Pregnant women ≥18 years, not living with HIV, and at 14-28 weeks gestation were enrolled in a PrEP clinical trial in Durban, South Africa between September 2017 and December 2019. Women were monitored 4-weekly during pregnancy until six months postpartum. We measured maternal weight and serum creatinine (sCr) at each visit and calculated creatinine clearance (CrCl) rates using the Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulae. Reference ranges for sCr and CrCl by CG and MDRD calculations were derived from the mean ± 2SD of values for pregnancy and postdelivery. RESULTS: Between 14--and 40 weeks gestation, 249 African women not exposed to TDF-PrEP contributed a total of 1193 renal function values. Postdelivery, 207 of these women contributed to 800 renal function values. The normal reference range for sCr was 30-57 and 32-60 umol/l in the 2nd and 3rd trimesters of pregnancy. Normal reference ranges for CrCl using the MDRD calculation were 129-282 and 119-267 ml/min/1.73m2 for the 2nd and 3rd trimesters, respectively. Using the CG method of calculation, normal reference ranges for CrCl were 120-304 and 123-309 ml/min/1.73m2 for the 2nd and 3rd trimesters respectively. In comparison, the normal reference range for sCr, CrCl by MDRD and CG calculations postpartum was 40-77 umol/l, 92-201, and 90-238 ml/min/1.73m2, respectively. CONCLUSIONS: In African women, the Upper Limit of Normal (ULN) for sCr in pregnancy is approximately 20% lower than 6 months postnatally. Inversely, the Lower Limit of Normal (LLN) for CrCl using either MDRD or CG equation is approximately 35% higher than 6 months postnatally. We provide normal reference ranges for sCr and CrCl for both methods of calculation and appropriate for the 2nd and 3rd trimesters of pregnancy in African women. Screening for pre-existing renal function disorders has become a routine clinical assessment for initiating TDF-containing antiretroviral treatment or pre-exposure prophylaxis in adults including pregnant women. Pregnancy inherently increases renal function, hence normal reference standards for non-pregnant adults cannot be used for pregnant women. In a secondary analysis of data from a healthy pregnant population not living with HIV who participated in a PrEP clinical trial, we established reference intervals for serum creatinine (sCr) concentration and creatinine clearance (CrCl) during pregnancy and postpartum in an African population. Using sCr and CrCl values for 249 healthy pregnant African women, we can confirm that the upper limit of normal for sCr in pregnancy is 20% lower than that for the 6-month postnatal period and recommend an upper limit of 57 umol/l and 60 umol/l in the second and third trimesters respectively to determine normal renal function in pregnant African women.We further determined the lower limit of normal for creatinine clearance using two methods of calculation, which was 35% higher than that of the postnatal period. Using the modification of diet in renal disease calculation, we recommend a lower limit of 129 and 119 ml/min/1.73m2 for the second and third trimesters respectively. Using the Cockcroft–Gault calculation, we recommend a lower limit of 120 and 123 ml/min/1.73m2 for the second and third trimesters respectively. Using current standard cut-off values estimated for adults may lead to underreporting of abnormal renal function in African pregnant women.
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