Urinary red blood cell and cast excretion in normal and hypertensive human pregnancy

Although the well-recognized pregnancy changes in renal blood flow, cellular function, tubular fluid composition, and flow rates may cause altered excretion rates of formed elements in the urine, relatively little attention has been paid to this in normal pregnancy. The urinary white cell excretion is known to be increased, with loss of the usual relationship between pyuria and urinary infection. Whether the same is true for other formed elements is unknown. Our purpose was to determine normal values for excretion of erythrocytes and casts and to establish whether they became abnormal in women in whom preeclampsia developed.

Study subjects were 174 continuously normotensive pregnant volunteers, 22 women who had preeclampsia, and 8 women who had chronic essential hypertension. Early-morning midstream urine samples were collected at 17 to 20 and at 33 to 36 weeks' amenorrhea after insertion of a vaginal tampon. Urinary microscopy was performed by standard techniques (Kesson et al. Lancet 1978;2:809).

The 95th percentile for concentration of erythrocytes was < or = 2500 red blood cells/ml; for casts the concentration was < or = 30 red blood cells/ml in normal pregnancy. Values for those who had preeclampsia and for the small group with chronic essential hypertension were within these limits.

In an early-morning concentrated urine sample, values of < or = 2500 erythrocytes/ml and < or = 30 hyaline or granular casts per milliliter can be accepted as normal.