How much do seemingly stable thyroid tests vary over time?
Most patients receiving thyroid replacement therapy with less than 125 mcg levothyroxine per day can wait 2 years before monitoring with thyroid stimulating hormone (TSH) if their level is normal. Fewer than 1 in 10 patients who take less than 125 mcg levothyroxine per day with a normal TSH level will have an abnormal laboratory value 1 year later. The likelihood goes up to 26.7% if the dosage is higher than 125 mcg levothyroxine per day. Patients with TSH levels closer to the upper or lower limits of normal will also be slightly more likely to have an abnormal value in 1 year. (LOE = 1b)
Pecina J, Garrison GM, Bernard ME. Levothyroxine dosage is associated with stability of thyroid-stimulating hormone values. Am J Med 2014;127(3):240-245.
Study design: Cohort (retrospective)
Funding source: Self-funded or unfunded
Setting: Outpatient (primary care)
These authors identified 715 patients (84% female, average age = 54 years) in a single primary care practice who were treated for hypothyroidism and had a normal TSH value (0.3 mIU/L - 5.0 mIU/L). They recorded all subsequent TSH levels in these patients for the following 6 years. Age, sex, body mass index, and history of chronic autoimmune thyroiditis were not associated with the development of a subsequent abnormal TSH level, but the dosage of levothyroxine was. Approximately 1 in 4 patients taking more than 125 mcg levothyroxine per day (26.7%) had an abnormal TSH level 1 year later. Most of the patients taking lower dosages (91.1%) had normal TSH levels 1 year later.
Allen F. Shaughnessy, PharmD, MMedEd
Professor of Family Medicine
How accurately does a midstream urine culture predict the results of a catheterized urine culture?
Midstream urine cultures with any evidence of Escherichia coli or Klebsiella pneumoniae strongly suggest a true infection, while the presence of enterococci and group B streptococci has little predictive value. This study confirms the practice of empirically treating suspected urinary tract infection in otherwise healthy women without relying on culture. Culture may still be of value when the diagnosis is unclear, in women with risk factors for complicated infection, and when women do not respond as expected to an initial round of antibiotics. In this case, ask the laboratory to provide information about the presence of gram-negative uropathogens using a lower cutoff value than the usual 1000 or 10,000 colony-forming units per milliliter. (LOE = 2b)
Hooton TM, Roberts PL, Cox ME, Stapleton AE. Voided midstream urine culture and acute cystitis in premenopausal women. N Engl J Med 2013;369(20):1883-1891.
Study design: Diagnostic test evaluation
Funding source: Government
These researchers recruited otherwise healthy nonpregnant women aged 18 years to 49 years who presented with acute cystitis to a primary care clinic in either Miami, Florida, or Seattle, Washington (N = 226). Those with signs of pyelonephritis or diabetes, or a history of recent infection or anatomic abnormalities were excluded. After obtaining a clean-catch midstream urine specimen, the women were catherized to obtain a second urine specimen. Of 236 episodes of cystitis, an adequate midstream specimen and an adequate catheterized specimen were obtained from 202. The median age of participants was 22 years, 73% were white, the median duration of symptoms was 2 days, and almost all presented with dysuria, urinary frequency, and urinary urgency. The catheterized specimen was positive for a uropathogen in 70% of the specimens, while the midstream culture was positive in 78%. Agreement was excellent between midstream and catheter cultures for the presence of gram-negative uropathogens, largely E. coli and Klebsiella pneumoniae. For gram-positive uropathogens such as enterococci and group B streptococci, midstream cultures were frequently positive (contaminated), but only rarely were these bacteria found in the catheterized specimen, as well. When staph saprophyticus was found, it was present in both cultures. The sensitivity of midstream culture compared with the catheterized culture decreased as the cutoff for a positive catheter culture (in CFU/mL) increased. Of course, as you increased this cutoff, the specificity increased. The positive predictive value of a midstream culture showing E. coli was higher than 90% at all cutoff values, including a cutoff of greater than or equal to 10 CFU/mL. However, the positive predictive value for enterococci and group B streptococci was poor at all cutoff values.
Mark H. Ebell, MD, MS
University of Georgia
POEMs are provided by Essential Evidence Plus, a point-of-care clinical decision support system published by Wiley-Blackwell. For more information, please see http://www.essentialevidenceplus.com(www.essentialevidenceplus.com).
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Top 20 POEMs of 2014