Ep 161: A 28-Year-Old Pregnant Woman with an Abnormal Urinalysis

In this episode, we discuss asymptomatic bacteriuria in a pregnant woman.

Read more on this topic in Harrison's.

Harrison's Principles of Internal Medicine, 22nd Edition

Transcript

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[Ms. Heidhausen] This is Katerina Heidhausen, executive editor of Harrison's Principles of Internal Medicine. Harrison's Podclass is brought to you by McGraw Hill's AccessMedicine, the online medical resource that delivers the latest content from the best minds in medicine. And now, on to the episode. 

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[Dr. Handy] Hi, everyone. Welcome back to Harrison's Podclass. We're your co-hosts. I'm Dr. Cathy Handy. 

[Dr. Wiener] And I'm Dr. Charlie Wiener, and we're joining you from the Johns Hopkins School of Medicine. 

[Dr. Handy] Today's episode is about a 28-year-old pregnant woman with an abnormal urinalysis. 

[Dr. Wiener] Cathy, this is two weeks in a row for pregnant women. Today's is a 28-year-old woman who recently found out that she's pregnant with her first child. She feels well and reports no symptoms other than mild morning nausea. As part of your initial visit, you obtain a urine specimen for dipstick and culture. The dipstick is negative for nitrite and leukocyte esterase, but two days later, it grows more than 10 to the 5th colony-forming units of E. coli. 

[Dr. Handy] All right, so we're talking broadly about urinary tract infections or UTIs. The terminology here is muddy, so let's just get some definitions out there before we get to the question. 

[Dr. Wiener] Okay, I'm listening. 

[Dr. Handy] UTI encompasses a spectrum of clinical entities. That includes asymptomatic bacteriuria, cystitis, prostatitis, and pyelonephritis. Obviously, no prostatitis in a pregnant woman. To be more precise, urinary tract infection denotes symptomatic disease; cystitis, symptomatic infection of the bladder; and pyelonephritis, symptomatic infection of the kidneys that involves the renal parenchyma. The distinction between symptomatic UTI and asymptomatic bacteriuria has major clinical implications. 

[Dr. Wiener] Before we get to the clinical indications, let's talk about epidemiology, 'cause I know there are differences based on age and sex. 

[Dr. Handy] Yes, except among infants and older adults, UTI occurs far more commonly in females than males. Between 1 year and about 50 years, UTI and recurrent UTI are predominantly diseases of females. As many as 50-80% of women in the general population acquire at least one UTI during their lifetime, uncomplicated cystitis in most cases. 

[Dr. Wiener] What are some of the risk factors? 

[Dr. Handy] For acute cystitis, recent use of a diaphragm with spermicide, frequent sexual intercourse, and a history of UTI are independent risk factors. In healthy postmenopausal women, sexual activity, diabetes mellitus, and incontinence are risk factors for UTI. And it is important to note that pyelonephritis can occur without symptomatic antecedent cystitis. 

[Dr. Wiener] How about men? 

[Dr. Handy] After age 50, obstruction from prostatic hypertrophy becomes common in men, and the incidence of UTI is almost as high among men as is among women. 

[Dr. Wiener] Great! So that gets us to our question. In this patient, which of the following statements is true? Option A, she is at risk for pre-term delivery. Option B, she should be re-cultured in two weeks. Option C, she should receive a single dose of ceftriaxone. Option D, she should receive five to seven days of trimethoprim/sulfamethoxazole. Or option E, the negative dipstick result rules out a treatable condition. 

[Dr. Handy] All right, this is important. The answer is A. In pregnant women, asymptomatic bacteriuria has important clinical consequences, and both screening for and treatment of this condition are indicated. Specifically, asymptomatic bacteriuria during pregnancy is associated with maternal pyelonephritis, which, in turn, is associated with preterm delivery. 

[Dr. Wiener] Do you treat that? 

[Dr. Handy] Yeah, appropriate antibiotic treatment of asymptomatic bacteriuria in pregnant women can reduce the risk of pyelonephritis, pre-term delivery, and low-birth-weight babies, so you do want to treat it. 

[Dr. Wiener] Okay. So, option B, re-culturing in two weeks, is false. We should not delay treatment. A number of the options dealt with therapy, and they were also wrong. So what is the appropriate therapy? 

[Dr. Handy] Ampicillin and the cephalosporins have been used extensively in pregnancy and are the drugs of choice for the treatment of asymptomatic or symptomatic UTI in pregnant women. 

[Dr. Wiener] Drugs to avoid? The question mentions trimethoprim/sulfamethoxazole. 

[Dr. Handy] It's one of the choices, but it should be avoided because of possible teratogenic effects and because of a possible role in the development of kernicterus. Fluoroquinolones, not mentioned here, but commonly also used for UTIs, those are also avoided because of possible adverse effects on fetal cartilage development. 

[Dr. Wiener] What about the duration of treatment? 

[Dr. Handy] Pregnant women with asymptomatic bacteriuria are treated for about four to seven days. There is no evidence to support single-dose therapy. If a pregnant woman develops pyelonephritis, she should receive parenteral beta-lactam therapy. 

[Dr. Wiener] Finally, talk for a moment about the dipstick test. 

[Dr. Handy] Understanding the parameters of the dipstick test is important in interpreting its results. Only members of the family Enterobacteriaceae convert nitrate to nitrite, and enough nitrite must accumulate in the urine to reach the threshold of detection. If a woman with acute cystitis is forcing fluids and voiding frequently, the dipstick test for nitrite is less likely to be positive, even when E. coli is present. The leukocyte esterase test detects this enzyme in neutrophils in the host's urine, whether the cells are intact or lysed. The bottom line for clinicians is that a urine dipstick test can confirm the diagnosis of uncomplicated cystitis in a patient with a reasonably high pre-test probability of this disease. Either nitrite or leukocyte esterase positivity can be interpreted as a positive result. But importantly, a negative dipstick test is not sufficiently sensitive to rule out bacteriuria in pregnant women, in whom it is important to detect all episodes of bacteriuria. 

[Dr. Wiener] So bottom line is pregnant women should be screened when they first are diagnosed with a urine culture in addition to the dipstick. 

[Dr. Handy] Yes, and that's consistent with the most recent guidelines from ACOG, too. That's the American College of Obstetricians and Gynecologists in 2023 on the topic. 

[Dr. Wiener] Great, so the teaching points in this case are that urinary tract infections or UTIs exist on a spectrum from asymptomatic bacteriuria to pyelonephritis. It's best to be specific with your language. Asymptomatic bacteriuria in a pregnant woman is a risk factor for complications and therefore should be treated with four to seven days of ampicillin or a cephalosporin. 

[Dr. Handy] You can find this question and other questions like it in the Harrison's Self-Review book, and then you can learn more about this topic in the Harrison's chapter on urinary tract infections. Visit the show notes for links to helpful resources, including related chapters and review questions from Harrison's, available exclusively on AccessMedicine. If you enjoyed this episode, please leave us a review so we can reach more listeners just like you. Thanks so much for listening. 

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