Kidney Stones 02: Labs

This is part of the four part PEMBlog series on kidney stones. Throughout you’ll learn about diagnosis and management of an increasingly recognized problem in the Pediatric Emergency Department.

Urinalysis

Hematuria

Though some patients have hematuria – many don’t. The moral of the story is that you should NOT use a negative U/A to exclude the possibility of a kidney stone. Though in adults, Luchs et al described the test characteristics of seeing blood on the U/A in patients with CT confirmed stones thusly;

  • Sensitivity=84%
  • Specificity=48%
  • Positive predictive value=72%
  • Negative predictive value=65%

Microhematuria was not seen in almost 60% of patients in a similar adult study from Xafis et al. As they noted “the presence or absence of blood on urinalysis cannot be used to reliably determine which patients actually have ureteral stones.”

A pediatric study (yes there are some) from Persaud et al. examined 95 patients with stones, and 15% had negative U/A for hematuria.

Crystals

They can be seen on the microscopic U/A. Don’t rely on them for diagnosis, and know that the type of crystal may help Urology in the future.

Pyuria and urine culture

Any febrile patient with a stone should be suspected of having a concurrent UTI/pyelo – the so-called “infected stone.” Both the presence of abc in the urine and + Nitrates have a level of evidence grade A in the European Association of Urology guideline.

Serum creatinine

Especially if you are going to be giving fluids and IV pain medicines (which is generally a good idea) you should be obtaining a measurement of the serum creatinine. Often obtained with electrolytes (renal panel, chem-7, BMP) an abnormal creatinine is concerning for dehydration (look for BUN:Cr > 20:1) or overt renal injury.

By |2015-09-18T12:14:11+00:00August 25th, 2015|Urology|

About the Author:

Brad Sobolewski, MD, MEd is an Associate Professor of Pediatric Emergency Medicine and an Assistant Director for the Pediatric Residency Training Program at Cincinnati Children's Hospital Medical Center. He is on Twitter @PEMTweets and authors the Pediatric Emergency Medicine site PEMBlog. All views are strictly my own and not official medical advice.