Urinary dipstick protein: a poor predictor of absent or severe proteinuria

Our purpose was to compare urinary protein dipstick values with standard 24-hour urinary protein excretion in women with hypertension in pregnancy.

Urinary protein dipstick determinations and concurrent 24-hour urinary protein excretion measurements were compared by review of 300 urine samples obtained from women with hypertension in pregnancy.

One hundred twenty-three samples had negative to trace protein on dipstick on two occasions at least 6 hours apart. Eight-one (66%) of these patients had significant proteinuria (> or = 300 mg per 24 hours). Seventy-six samples revealed 3+ to 4+ protein on dipstick in at least two samples. Of these, 27 (36%) had heavy proteinuria (> or = 5 gm per 24 hours), and 42 (55%) had nephrotic range proteinuria of > or = 3.5 gm per 24 hours. One hundred one patients had urine dipstick values of 1+ to 2+, of whom 89 (88%) had significant proteinuria.

Urinary protein dipstick values > or = 1+ have a positive predictive value of 92% (162/177) for predicting > or = 300 mg per 24 hours. In contrast, a dipstick of negative to trace should not be used to rule out significant proteinuria because its negative predictive value is only 34% (42/123) in hypertensive patients. Moreover, urine dipstick values of 3+ to 4+ should not be used to diagnose severe preeclampsia because their positive predictive value is only 36% (27/76).