PP024. Random urine albumin: Creatinine ratio in high-risk pregnancy - Is it clinically useful?

The albumin:creatinine ratio (ACr) is the newest of available methods of proteinuria assessment in pregnancy. Published cut-offs for detection of ⩾0.3g/d proteinuria vary from 2mg/mmol to 8mg/mmol. Up to 20% of women have an elevated ACr in pregnancy but normal outcome. In addition, it is our impression that the urine albumin component of the ACr is frequently below the detection limit of the assay.

To evaluate the frequency with which a measurable ACr can be obtained in a high-risk outpatient maternity population.

In this prospective cohort study, consecutive inpatients or outpatients (attending primarily morning high-risk maternity clinics) were evaluated at a tertiary care facility. Random midstream urine samples were obtained as part of normal clinical care. In the hospital laboratory, urinary albumin was measured using an immunoturbidimetric method, and urinary creatinine by an enzymatic method, both on an automated analyser (Vitros® 5,1 FS or Vitros® 5600, Ortho-Clinical Diagnostics, Rochester NY). ACr was calculated for samples with measurable urine albumin, and for samples with albumin below the assay range, ACr was calculated using the assay cut-off for albumin of 6.00mg/L.

One hundred and sixty women (81.9% outpatients) were screened at one/more antenatal visits, providing a total of 233 urine samples for analysis. 68 (29.2%) urine samples were dilute (i.e., had urinary creatinine <3mM); only 13 (19.1%) of these had measurable urinary albumin for calculation of the ACr. Overall, 117/233 samples (50.2%) had measurable urine albumin that could be used to calculate the ACr. 76 (65.0%) had ACr >2mg/mmol and 34 (29.1%) had ACr >8mg/mmol. For the 116/233 (49.8%) samples with urine albumin below the assay detection limit, ACr was calculated using 6.00mg/L as the value for urine albumin. All of the 55 dilute samples had an ACr >2mg/mmol and 3 (2.6%) had an ACr >8mg/mmol. If dilute samples were excluded, none of the remaining 61 samples had an ACr value >2mg/mmol.

Among a population of pregnant women attending primarily morning high-risk maternity clinics, urine is often dilute and urine albumin is often below the assay detection limit. This combination may result in uninterpretable ACr values if an ACr cut-off of 2mg/mmol is used as the decision limit for proteinuria ⩾0.3g/d. ACr may be best performed on first voided (concentrated) urine if ACr is used to assess proteinuria in pregnancy.