Chapter 21: NEPHROLOGY

THE URINALYSIS

MICROSCOPIC HEMATURIA

Microscopic hematuria is defined as greater than 5 RBCs per HPF. Unless there are overt symptoms, DO NOT get too aggressive initially. Repeat the urinalysis in 2 weeks, and if there is still a problem, then start a workup. Look for systemic symptoms and a family history of any renal disease. The first step for a question on the pediatric boards is to get a URINE CALCIUM AND URINE CREATININE. If that option is not available, you can choose to obtain imaging (renal ultrasound), serum BUN, serum creatinine, coagulation studies, platelet count, ANA, anti-DS DNA, complement levels or sedimentation rate (ESR) depending on the clinical picture. If the values of the urine calcium and urine creatinine are given, calculate a urine calcium-to-creatinine ratio on the random sample of urine. If it’s > 0.25, do a hypercalciuria workup (see below). If the value is < 0.25 on the random sample, get a renal ultrasound to look for structural anomalies.

• PEARL: On imaging, you would especially be looking for evidence of ureteropelvic junction (UPJ) obstruction (dilated calyces). This would have to be confirmed with a MAG3/furosemide scan showing delayed excretion to make the diagnosis.
• PEARLS: CYSTOSCOPY IS RARELY NEEDED for hematuria in pediatrics. So don’t pick it. Also, during any imaging if there is a structural issue noted in one kidney, check the other one too. Lastly, if you are given a vignette in which a track athlete has a positive urine dipstick for blood, and there are only a few RBCs per HPF on microscopy, the patient has MYOGLOBINURIA.
• HYPERCALCIURIA: This is probably your answer for persistent hematuria in an otherwise healthy kid. Obtain a urine calcium-to-creatinine ratio. If the value is > 0.25, the patient has hypercalciuria. This can be a stand-alone problem or due to loop diuretics (furosemide). If the ratio is > 0.25, calculate the ratio again from a 24-hour urine collection to see if it’s > 4.0. If so, then get a renal ultrasound to look for a stone because this CAN be associated with nephrolithiasis (symptoms may include dysuria and abdominal pain).
  • NAME ALERT/PEARL:  Hypercalciuria is not the same thing as familial hypercalcemic HYPOcalciuria. This is not associated with hematuria and is benign. The name says it all for this other disease. Look for a family history of it, hypercalcEMIA and HYPOcalciuria (the urine calcium-to-creatinine ratio would be less than 0.25).

PROTEINURIA

Proteinuria is often benign and due to orthostasis (meaning children get it when they have been upright for a while). They may also get transient proteinuria from general medical illnesses and dehydration. If it’s said to be 1+, just repeat in 2 weeks. If it’s 2+ or greater, you HAVE to do a workup. First, order a urinalysis on an AM void and on a second urine specimen obtained in the office. If there is NO PROTEIN noted on the AM void and a normal urinalysis, this is probably due to transient proteinuria (which CAN indeed cause 2+ proteinuria). If there is NO PROTEIN noted on the AM void and THERE IS proteinuria on the office sample, it’s likely due to orthostatis. If THERE IS proteinuria on the AM void and THERE IS proteinuria on the second urine sample, this indicates persistent proteinuria. Obtain additional urine samples for urinalysis with microscopy, order bloodwork (BUN, creatinine, serum electrolytes, cholesterol, albumin, and total protein) and obtain a blood pressure. If the proteinuria continues to persist, or if any of the labs are abnormal, obtain a 24-hour urine protein collection.

PEARLS:  Urine protein:creatinine cut-off is 0.2. Urine calcium:creatinine cut off is 0.25.