We evaluated the frequency of measurable albuminuria (⩾6.00mg/L) for albumin:creatinine ratios (ACr) among 160 consecutive women attending high-risk clinics. Of last urine samples before delivery, 76 had measurable albuminuria and 41/76 (53.9%) had ACr ⩾2mg/mmol of which 7.3% had normal pregnancy outcome. 84 samples had albuminuria <6.00mg/L and 43/84 (51.2%) had ACr ⩾2mg/mmol of which 25.6% had normal pregnancy outcome (p=0.025). Excluding 48/160 (30.0%) dilute samples (urinary creatinine <3mM), no samples with unmeasurable albuminuria had ACr ⩾2mg/mmol. In pregnancy, urine is often dilute and without measurable albuminuria, leading to a clinically relevant proportion of false positive results by ACr.