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.
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;
- 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.
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.
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.