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08/04/2011 - Sono for choledocholithiasis and nitrites

posted Sep 20, 2011, 5:40 AM by Chief Resident   [ updated Sep 20, 2011, 5:33 PM by Purnema Madahar ]
The interns are completing the first call cycle of the month and we're all getting ready for the end of the week. Let's get some preparatory logistics for the weekend out of the way:

1. Please all remember weekend social work rounds at 3:00 tomorrow. Residents, please sign out all potential weekend discharges to the social workers. Interns, come for the treats!
2. Please check the detailed weekend coverage sheets; they should be up on the white board before noon.
3. Residents on call tomorrow are on for 24+6 hours. Don't forget to pick up your sub-interns boards in the morning. The sub-interns on call will come in at 8:00 pm.

This morning's resident report was a Red Team affair: Zach Rosner presented a great case to Bob Goodman in a hybrid patient-presentation-meets-journal-club session:

In a patient s/p cholecystectomy with RUQ pain and the clinical suspicion for choledocholithiasis, who had a RUQ sonogram negative for stones, what's the likelihood of her having a stone?

The attached paper prospectively compared ultrasound to ERCP (as the gold standard) in a population with very similar characteristics to our patient. We thought that her per-test probability was similar to the prevalence in the polulation studied and therefore concluded that her post-test probability of having a stone was 36% given the negative predictive value of 64% determined in the study.

While talking about the differential diagnosis, Natalie Zelta made a good case for a perinephric abscess that raised some questions. It seems that most research on perinephric abscesses was published in the 70s and 80s, so I couldn't pull any original electronic papers. Answers come from Dembry LM, Andriole VT: Renal and perirenal abscesses. Infect Dis Clin North Am. 1997;11(3):663, (Einstein library login required)

Q: How often does a perinephric abscess present without pyuria?
A: Pyuria and proteinuria are common; however, the urinalysis may be normal up to one third of the time, and 40% of patients have sterile urine.

Q: What is the sensitivity of ultrasound to detect a perinephric abscess?
A: The ultrasound will show a sonolucent mass, often with irregular walls, and may be multiloculated with internal echoes. In one study, however, the ultrasound was falsely negative in 36% of cases when compared to CT evaluation

Q: What bacteria produce nitrite on a urine dipstick?
A: ...include Escherichia coli, Klebsiella, Proteus, Staphylococcus, and Pseudomonas, to mention a few that are frequent causes of urinary tract infections...... (K McClatchey: Clinical Laboratory Medicine, page 528)

Get ready for more learning: CRS with Jerry Paccione tomorrow at 12:15. Be on time!

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