Problematically, the optimal method of establishing abnormal levels of either urine protein or albumin remains to be defined. For a 24-hour quantitative specimen, the "consensus" threshold value used is �300 mg/24 h (American College of Obstetricians and Gynecologists, 2013). Using a urinary protein excretion threshold of 165 mg in a 12-hour sample shows equivalent eicacy (Stout, 2015; Tun, 2012).
Determination of urinary protein:creatmme ratio may supplant the cumbersome 24-hour quantiication (Kyle, 2008; Morris, 2012). Chen and associates (2008) found that clean-catch and catheterized urine specimens correlate well. In one systematic review, random urine protein:creatinine ratios below 130 to 150 mg/ g, that is, 0.13 to 0.15, indicate a low likelihood of proteinuria exceeding 300 mg/ d (Papanna, 2008). Ratios <0.08 or > 1.19 have negative-or positive-predictive values of86 and 96 percent, respectively (Stout, 2013). However, midrange ratios, that is, 300 mg/g or 0.3, have poor sensitivity and specificity. Thus, many recommend that with midrange ratio values, 24-hour protein excretion should be quantified.
With urine dipstick assessment, determinations depend on urine concentration and are notorious for false-positive and -negative results. hus, assessment may show a dipstick value of 1 + to 2+ from concentrated urine specimens from women who excrete < 300 mg/ d.
Importantly, proteinuria may develop late, and some women may already be delivered or have had an eclamptic convulsion before it appears. For example, 10 to 15 percent of women with HELLP syndrome do not have proteinuria at presentation (Sibai, 2004). In one report, 17 percent of eclamptic women did not have proteinuria by the time of seizures (Zwart, 2008).
Sheehan and Lynch (1973) frequently found changes identifiable at autopsy by light and electron microscopy in the kidneys of eclamptic women. Glomeruli are enlarged by approximately 20 percent, they are "bloodless," and capillary loops variably are dilated and contracted. Endothelial cells are swollen-termed glomerular capillay endotheliosis (Spargo, 1959). Endothelial cells are often so swollen that they block or partially block the capillary lumens (Fig. 40-7) (Hecht, 2017). Homogeneous subendothelial deposits of proteins and fibrin-like material are seen.
Endothelial swelling may result from angiogenic protein "withdrawal" caused by the complexing of free angiogenic proteins with a compatible circulating antiangiogenic protein receptor (see Fig. 40-3). The angiogenic proteins are crucial for podocyte health, and their inactivation leads to podocyte dysfunction and endothelial swelling (Conrad, 2015; Karumanchi, 2009). Also, eclampsia is characterized by greater excretion of these epithelial podocytes (Wagner, 2012; White, 2014).