Proteinuria, Orthostatic Proteinuria
- Proteinuria is the most ominous finding in urinalysis suggestive of renal
- In general, the pore size of the glomerular basement membrane (GBM) is
relatively small, but a small amount
of protein can be detected in the urine of any individual.
- However, if the integrity of the GBM is compromised, larger proteins may
enter the urine.
- The most abundant protein in the
urine usually is albumin, owing to its comparatively small size.
transferrin, vitamin D, and
III may leak into the urine if the
If urinalysis reveals protein in the urine of any child, an evaluation is
- The urine also should be assessed for the presence of red blood cells (RBCs),
white blood cells, nitrites, and bacteria.
and protein on urinalysis suggest renal parenchymal disease or urinary
- Nitrites or bacteria in a
clean-catch or catheterized specimen strongly indicate urinary tract
- Most patients who have
do not have edema due to a reduction of oncotic pressure.
In the absence of symptoms
such as edema, abdominal or flank pain, dysuria, or fever, evaluation of
proteinuria can proceed in a stepwise manner.
- The most prudent initial step is to obtain a first-morning specimen and
repeat the urinalysis.
- If the specimen is negative for protein, the diagnosis of orthostatic
proteinuria (OP) can be made.
- If there is protein in the urine on a first-morning specimen, protein and
creatinine in the urine should be quantitated.
- A urine protein:urine creatinine ratio (mg/mg), in a single voided sample,
greater than 0.2 is abnormal; above 1.0 is nephrotic range proteinuria
- A P/C greater than 0.25 on the first-morning specimen warrants further
- If the protein/creatinine (P/C) ratio is less than 0.25, observation and
repeat measurement of the ratio within the next month are appropriate.
- Urine protein measured in a 12-or 24-hour urine collection:
- Protein excretion of less than 4 mg/m2 per hour is normal
- Protein >40 mg/m2 per hour is considered in the nephrotic range
- total urinary protein excretion is elevated while the child is in an
upright position and exceeds the rate seen in the recumbent position
- urinary protein excretion rarely exceeds 1 g/day
- diagnosis based on comparison of urine in the recumbent vs. upright
- finding of proteinuria
by dipstick on a random (mid-day) sample and a completely negative
finding by dipstick on the first-morning sample.
- benign condition, does not portend
long-term risk for subsequent renal disease
- Its cause remains obscure, but it
may be related to compression of the renal vein from the kidney
- Regardless of the mechanism, affected patients do not require periodic
- OP cannot be the ultimate diagnosis in a patient who has RBCs in the
- A family history always is essential in the evaluation of any patient,
although there is no evidence that OP is a familial disease
- The benign nature of OP obviates the need for a consultation with a
- false-positive result for protein in the urine may be seen in a sample
that is extremely alkaline (urine pH, >8.0).
- Proteinuria may be masked with a very dilute urine (specific gravity,
- Protein also may be transiently present in the urine of patients who have
fever or acute illness. It is prudent to re-examine the urine at a later date
in these patients.
eventually may be necessary in a patient who has
that does not disappear on the first- morning specimen. A
24-hour urine collection for protein
determination also is reserved for patients who have proof of protein in the
urine on the first-morning specimen.
CHLA Board Review 2005
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Loghman-Adham M. Evaluating proteinuria in children. Am Fam Physician.
Wingo CS, Clapp WL. Proteinuria: potential causes and approach to
evaluation. Am J Med Sci. 2000;320:188-194