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The measurement of proteinuria is no less problematic. The urinary protein excreted in the condition pre-eclampsia arises as a result of glomerula endotheliosis. However, it also indicates a generalised increase in capillary permeability in other organ systems of the body (Reference1). The presence of significant proteinuria does act as a marker for the severity of the disease pre-eclampsia and patients who suffer from hypertension and proteinuria are at an increased risk of small for gestational age fetuses and perinatal mortality as well as maternal morbidity (Reference2).

The most commonly used screening method is dipstix testing of a random urine sample. These however are notoriously inaccurate. Several published papers have shown a poor positive predictive value for the presence of protein as identified by the dipstix as well as high false negative rates. One plus (+) of protein on the dipstix is said to approximate to 300 mgs of protein loss in a 24 hour urine collection. This level is the upper limit of normal in pregnancy. However the measure depends upon the concentration of the urine, which will fluctuate with fluid in take and the timing of the urine specimen. Two pluses (++) on a dipstick is more secure when making the diagnosis of significant proteinuria.

However, all dipstick testing needs to be confirmed with 24 hour urine collections which are currently accepted as the "gold standard" for quantification of urinary protein loss. As we will see later, these too have their problems.

Automated analysis eliminates observer variability associated with the dipstix and it has been shown to increase the sensitivity for the measurement of proteinuria (Reference3). The spot urine protein: creatinine ratio, which is a newer method for quantifying protein loss, correlates well with a 24 hour urine collection and has several advantages. This technique improves detection of proteinuria and allows for the concentration of the urine in quantifying protein loss. The results are evidently quicker than the 24 hour urine collection which is inconvenient and difficult particularly for some women.

Despite the difficulties in quantifying proteinuria in pregnancy when the disease process of pre-eclampsia is viewed in the round, it is a useful marker of severity. It is incumbent upon clinicians to recognise the deficiencies in the measurement techniques, for proteinuria and blood pressure; and ensure that all borderline measurements are repeated in order that women are not wrongly labelled with the diagnosis of pre-eclampsia. It should also be noted that the disease may present in different ways without significant proteinuria. This issue will be raised in the next section on the definitions and classification of the hypertensive disorders in pregnancy.


1. Brown MA. Capillary permeability and extra cellular fluid volumes in pregnancy-induced hypertension. Clin Sci 1989;77:599-604, Abstract
2. Halligan AW. Dipstick proteinuria: caveat emptor. Br J Obstet Gynecol 1999;106:1113-5, Abstract
3. Saundan PJ. Improved methods of assessing proteinuria in hypertensive pregnancy. 1997;104:1159-64, Abstract

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