STEAMBOAT SPRINGS, COLO. – Primary care physicians commonly over-refer children for subspecialist nephrologic evaluation of proteinuria they could readily identify as nonpathologic in their own offices by simple testing, thereby sparing families considerable expense and anxiety.
All that’s needed to differentiate pathologic from nonpathologic causes of proteinuria is a properly obtained first morning voided urine specimen for dipstick testing and laboratory spot measurement of the urine protein/creatinine ratio, according to Dr. Beth A. Vogt, a pediatric nephrologist at Rainbow Babies and Children’s Hospital and Case Western Reserve University, Cleveland.
Dr. Beth A. Vogt
If the urinalysis shows no or only 1+ protein and a protein/creatinine ratio below 0.2, the patient and family can be reassured that there’s no problem. End of story. No need for the family to sweat out the weeks of delay likely required to see a pediatric nephrologist, she said at a meeting on practical pediatrics sponsored by the American Academy of Pediatrics.
Proteinuria is quite common in children. Roughly 10% of 8- to 15-year-olds will have proteinuria on a single screening dipstick sample. But upon repeat testing, this time using a first morning void sample rather than a urine specimen obtained during office hours, this figure drops from 10% to less than 1%.
This much smaller subgroup with persistent proteinuria should be presumed to have kidney disease until proven otherwise via nephrologic evaluation, she emphasized.
The urine protein/creatinine ratio is a simple quantitative test that’s ordered by checking off the spot protein and creatinine levels on a standard lab slip. This test has largely replaced the classic 24-hour urine collection.
"The 24-hour urine collection is a cumbersome, error-prone test that we’ve outgrown in pediatric nephrology. We don’t do this very much anymore. People tend to either over- or undercollect," Dr. Vogt explained.
The urine dipstick is a good, relatively cheap tool. But it’s important to recognize that false-positive results are common if the urine pH is more than about 8.0 or if the urine is concentrated, as is common because kids tend to drink less than they should.
"A 1+ proteinuria in a kid who has a urine specific gravity greater than 1.015 is really not an issue. If you recognize that it is normal, you can really save yourself a lot of trouble. Let it be," she advised.
The most common type of proteinuria is transient proteinuria accompanying a febrile illness, dehydration, urinary tract infection, or exercise. This is self-limited proteinuria that will resolve after the underlying condition resolves. If Dr. Vogt finds 1+ proteinuria under these circumstances, she typically doesn’t bother to retest later, as long as the patient has no history of renal disease or suggestive symptoms.
Orthostatic proteinuria is another common benign condition. Indeed, it is seen in 2%-5% of adolescents. For reasons as yet unknown, affected patients produce protein only in urine generated while they are in an upright position. Urine produced while they are supine is negative for protein, which is why testing a first morning voided specimen is so illuminating.
The family needs careful instruction in how to obtain an all-supine urine sample. The child should empty the bladder completely immediately before bedtime. The next morning the sample must be collected immediately after getting up.
Persistent proteinuria as evidenced by a positive first morning urinalysis indicates kidney disease. Among the more common causes are membranous nephropathy; polycystic kidney disease; renal scarring due to reflux nephropathy; renal dysplasia; and focal segmental glomerulosclerosis, which is on the rise as a result of the obesity epidemic.
In addition to arranging a referral to a nephrologist for the patient with persistent proteinuria, the primary care physician can help expedite matters by ordering a renal function panel, an antinuclear antibody test, C3 and C4, and a renal ultrasound. These are studies the pediatric nephrologist will want to have, Dr. Vogt said.
She reported having no relevant financial conflicts.