By Rebecca H. Allen, MD, MPH, Editor
SYNOPSIS: This systematic review found that urine dipsticks of 1+ protein had a sensitivity of only 68% for the diagnosis of preeclampsia (95% confidence interval, 0.57-0.77), which was considered poor. Performance improved at thresholds of 2+ and 3+ protein.
SOURCE: Teeuw HM, Amoakoh HB, Ellis CA, et al. Diagnostic accuracy of urine dipstick tests for proteinuria in pregnant women suspected of preeclampsia: A systematic review and meta-analysis. Pregnancy Hypertens 2022;27:123-130.
Preeclampsia is a hypertensive disorder in pregnancy that is defined as high blood pressure ≥ 140/90 mmHg at 20 weeks gestation or more, typically accompanied by the presence of proteinuria. If there is no proteinuria, then preeclampsia can be diagnosed by the presence of new onset hypertension accompanied by thrombocytopenia, renal insufficiency, impaired liver function, pulmonary edema, or new onset headache unresponsive to medication or not accounted for by another diagnosis.1 Some preeclampsia definitions also include intrauterine fetal growth restriction as another diagnostic criterion.2
The diagnosis of proteinuria can be made by finding 300 mg or more of protein in a 24-hour urine collection, a protein/creatinine ratio of 0.3 or more, or a urine dipstick protein reading of 2+.1 In-office urine dipsticks commonly are used at prenatal visits to screen for and diagnose preeclampsia. The typical readings are 1+ equals 0.3 g/L, 2+ equals 1 g/L, and 3+ equals 3 g/L of protein. The authors of this study sought to determine the reliability of urine dipstick protein measurements for the diagnosis of preeclampsia.
This systematic review searched for articles in MEDLINE, EMBASE, and the Cochrane Library from inception until August 2020. Keywords included “preeclampsia,” “hypertension in pregnancy,” or “proteinuria in pregnancy” combined with “dipstick” or “urinalysis.” The inclusion criteria were articles of diagnostic accuracy studies on urine dipstick tests compared to a gold standard (protein/creatinine ratio or 24-hour urine protein) of pregnant women ≥ 20 weeks gestation in any language. Women could have been suspected of having preeclampsia or undergoing routine proteinuria assessment.
A total of 19 studies were included in the review, with nine studies enrolling women specifically suspected of having preeclampsia and 10 studies including a more heterogeneous group of women (suspected of preeclampsia and other indications for proteinuria testing). The overall pooled sensitivity and specificity of urine dipstick for the 1+ threshold was 0.68 (95% confidence interval [CI], 0.57-0.77) and 0.85 (95% CI, 0.73-0.93), respectively (n = 3,700 samples, 18 studies). The positive predictive value, assuming a prevalence of 25%, was 61%. Using a threshold of 2+, the sensitivity was lower (0.45; 95% CI, 35-55) but the specificity was higher (0.97; 95% CI, 92-99) and the positive predictive value, assuming a prevalence of 25%, was higher at 84%. There was no large difference between automated dipsticks and visually read dipsticks.
COMMENTARY
Preeclampsia is an important cause of maternal morbidity and mortality in the United States and internationally. Urine dipsticks commonly are used in the office during prenatal care to screen for and diagnose preeclampsia. In terms of routine screening at each prenatal visit, the American College of Obstetricians and Gynecologists (ACOG) states that in the absence of risk factors for urinary tract infections (UTIs), renal disease, and preeclampsia, and in the absence of symptoms of a UTI, hypertension, or unusual edema, the routine urine dipstick for protein can be omitted.3 However, urine dipsticks still have a role in some settings in the diagnosis of preeclampsia, especially settings that lack access to laboratory facilities. The International Society for the Study of Hypertension in Pregnancy (ISSHP) recommends that, “When neither 24-hour nor protein/creatinine ratio measures of proteinuria are available, dipstick testing provides reasonable assessment of true proteinuria, particularly when values are > 1 g per liter, that is, 2+.”2
The results of this study did not find that urine dipsticks were very sensitive for the diagnosis of preeclampsia; however, the specificity and the positive predictive value of the test increased for each threshold measured: 1+, 2+, and also 3+. Therefore, if no other test is available, then it certainly is reasonable to use them. However, results may need to be confirmed with laboratory testing, but a urine dipstick could flag a patient for further evaluation. Similarly, a negative result should be followed up on in a patient with continued symptoms in case the result is a false negative. There are limitations to urine dipstick testing for protein, for example, if the urine is very dilute.
The limitations of this study are those that plague most meta-analyses. Namely, the quality of the meta-analysis is only as good as the studies that comprise it. The studies included in this meta-analysis were performed in a variety of settings with different patient populations. Thirteen studies were from high-income countries and six were from middle-income countries. Additionally, some used 24-hour urine protein as the comparison, and some used the spot protein/creatinine ratio. All in all, this investigation likely will not change our current practice for the use of urine dipsticks in the office. Currently, we only check urine protein on dipstick for prenatal patients with chronic hypertension or those suspected of developing gestational hypertension or preeclampsia. If positive, the urine dipstick result is followed up with a spot protein/creatinine ratio, which we now use more commonly than a 24-hour urine protein collection because of its ease of use and more rapid results. If the dipstick for protein is negative, we are reassured, but always vigilant in tracking the patient’s symptoms and order repeat testing as needed.
REFERENCES
- [No authors listed]. Gestational hypertension and preeclampsia: ACOG practice bulletin, number 222. Obstet Gynecol 2020;135:e237-e260.
- Brown MA, Magee LA, Kenny LC, et al. Hypertensive disorders of pregnancy: ISSHP classification, diagnosis, and management recommendations for international practice. Hypertension 2018;72:24-43.
- American College of Obstetricians and Gynecologists and the American Academy of Pediatrics. Guidelines for Perinatal Care, eighth edition. Washington, DC;September 2017.
