Preeclampsia: Questions of Diagnosis and Treatment

In their "What's The 'Take Home'?" case of a pregnant woman with hypertension (CONSULTANT, April 1, 2005, page 473), Drs Lawrence Kaplan and Ronald Rubin inquire into the most likely cause of the patient's elevated blood pressure. This 35-year-old patient had blood pressure measurements of 148/ 94 mm Hg at 28 weeks' gestation and 146/94 mm Hg at 32 weeks' gestation (2 years earlier her blood pressure was normal). Urinalysis revealed 1+ pro- teinuria. Based on this information, the authors correctly conclude that preeclampsia is the most likely diagnosis.

However, this information is not sufficient to make a definitive diagnosis. The diagnostic criteria for preeclampsia indeed include the new onset of elevated blood pressure (diastolic pressure of at least 90 mm Hg or systolic pressure of at least 140 mm Hg) and proteinuria (defined as the presence of 300 mg or more of protein in a 24-hour urine collection after 20 weeks' gestation). Although this level of urinary protein excretion may correlate with a 1+ dipstick reading, it is recommended that the diagnosis of preeclampsia be based on the protein in a 12- to 24-hour urine collection.^1-3 The reason for this recommendation is the very high false-positive rate for 1+ protein dipstick readings; alkaline urine, concentrated urine, and the presence of ketones all falsely elevate protein levels on dipstick readings.^3,4 Thus, reliance on the dipstick may lead to overdiagnosis of preeclampsia.

— Mark Shatsky, DO
   Clinical Assistant Professor of Family Medicine
   Kansas City University of Medicine and Biosciences
   Kansas City, Mo
   Assistant Director
   Deaconess Family Medicine Residency
   Evansville, Ind

REFERENCES:
1. ACOG Committee on Obstetric Practice. ACOG practice bulletin. Diagnosis and management of preeclampsia and eclampsia. Number 33, January 2002. American College of Obstetricians and Gynecologists. Int J Gynaecol Obstet. 2002;77:67-75.
2. National Heart, Lung, and Blood Institute. National High Blood Pressure Education Program: Working Group Report on High Blood Pressure in Pregnancy. Bethesda, Md: National Institutes of Health; 2000. Publication 00-3029. Available at: http://www.nhlbi.nih.gov/health/prof/heart/hbp/hbp_preg.htm. Accessed June 7, 2005.
3. Phelan LK, Brown MA, Davis GK, Mangos G. A prospective study of the impact of automated dipstick urinalysis on the diagnosis of preeclampsia. Hypertens Pregnancy. 2004;23:135-142.
4. Wagner LK. Diagnosis and management of preeclampsia. Am Fam Physician. 2004;70:2317-2324.

In their case of hypertension in a pregnant woman, I was surprised that Drs Kaplan and Rubin did not include nifedipine (either short-acting or long-acting) in their discussion of drug treatments.

Also, the authors gave 100 mm Hg as the diastolic blood pressure cutoff for initiation of antihypertensive therapy in pregnancy; I recall reading elsewhere in the literature that the cutoff should be 110 mm Hg.

— Robert P. Blereau, MD
   Morgan City, La

We appreciate the issues raised by Drs Shatsky and Blereau. Our case was meant to illustrate the constellation of symptoms of preeclampsia. Although dipstick urinalysis is 95% to 99% sensitive,¹ the definitive diagnosis of proteinuria does require a more accurate assessment. The patient ultimately had a 24-hour urine collection that demonstrated 450 mg of protein. The standard definition of hypertension in pregnancy is serial measurements of at least 140/90 mm Hg, or an individual measurement of at least 160/110 mm Hg.²

Although nifedipine has been used in preeclampsia,² it is classified as FDA category C and is thus less useful than methyldopa, hydralazine, and labetalol in this setting. Moreover, nifedipine has significant tocolytic effects³ that may be detrimental in patients with preeclampsia, especially if expedient delivery is necessary.

— Lawrence I. Kaplan, MD
   Associate Professor of Medicine
   Ronald N. Rubin, MD
   Professor of Medicine
   Temple University School of Medicine