Prevalence and implications of isolated microscopic hematuria in asymptomatic Chinese pregnant women.

Background: IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. However, the actual prevalence of microscopic hematuria and IgAN is unknown in the Chinese population.

Methods: We screened 7,828 consecutive pregnant women for microscopic hematuria in the antenatal clinic of a tertiary referral center. Persistent microscopic hematuria was defined as urine Hemastix (Bayer Diagnostics, Hong Kong) of 1+ for red cells in two clinic visits. Subjects were referred to the renal clinic for specialist evaluation, including measurement of blood pressure, serum creatinine, urine bacterial culture, and quantification of proteinuria.

Result: There were 207 women (2.64%) with microscopic hematuria. Mean age was 31.8 +/- 5.0 years. In 101 patients (48.8%), there was proteinuria >0.1 g/day by quantitative assay. Hematuria was found to resolve before or shortly after delivery in 126 (60.9%) and 68 women (32.9%), respectively. Five patients (2.4%) had urinary tract infection proved by repeated urine culture, 1 had papillary necrosis, and 1 had duplex collecting system. Three patients were confirmed to have IgAN by renal biopsy; all had normal blood pressure and serum creatinine, but dysmorphic red cells in urine microscopy, and proteinuria of over 0.5 g/day that persisted after delivery. Renal biopsy on another woman showed no specific pathology. Two women were lost to follow-up, both with normal renal function and no detectable proteinuria. The overall prevalence of IgAN was 38 cases per 100,000 population (95% confidence interval: 8-112 cases).

Conclusion: Microscopic hematuria is not uncommon in pregnant women, and IgAN is present in a small proportion of these patients. Further study is needed to determine whether screening for microscopic hematuria would allow early diagnosis and improve the prognosis of these patients.