EVALUATION OF ASYMPTOMATIC PROTEINURIA IN CHILDREN

By: Patricia Baile

MECHANISMS OF PROTEIN HANDLING BY KIDNEY

Glomerular capillary wall permits passage of small molecules while restricting macromolecules

3 components of glomerular wall Endothelial cell Basement

membrane Epithelial cell

MECHANISMS OF PROTEIN HANDLING BY KIDNEY

Glomerular permeability

Steric hindrance: due to spatial alignment of the passing molecules, relative to membrane pores

Viscous drag: impedance to movement caused by fluid lining the pores

Electrical hindrance: due to electrostatic repulsion between epithelial surface and plasma proteins

MECHANISMS OF PROTEIN HANDLING BY KIDNEY

Normal protein excretion affected by interplay of glomerular and tubular mechanisms

Glomerular injury: abnormal losses of intermediate MW proteins like albumin

Tubular damage: increased losses of low MW proteins

NORMAL PROTEIN EXCRETION Normal protein excretion

Child: < 100mg/m2/day or 150mg/day Neonates: up to 300mg/m2

ABNORMAL PROTEIN EXCRETION Urinary protein excretion in excess of

100 mg/m2 per day or 4 mg/m2 per hour

Nephrotic range proteinuria (heavy proteinuria) is defined as ≥ 1000 mg/m2 per day or 40 mg/m2 per hour.

ABNORMAL PROTEIN EXCRETION Glomerular proteinuria

Due to increased filtration of macromolecules

May result from glomerular disease (most often minimal change disease) or from nonpathologic conditions such as fever, intensive exercise, and orthostatic (or postural) proteinuria

ABNORMAL PROTEIN EXCRETION Tubular proteinuria

Results from increased excretion of low molecular weight proteins such as beta-2-microglobulin, alpha-1-microglobulin, and retinol-binding protein

Tubulointerstitial diseases, can lead to increased excretion of these smaller proteins

ABNORMAL PROTEIN EXCRETION Overflow Proteinuria

Results from increased excretion of low molecular weight proteins due to marked overproduction of a particular protein to a level that exceeds tubular reabsorptive capacity

ASYMPTOMATIC PROTEINURIA

Levels of protein excretion above the upper limits of normal for age

No clinical manifestations such as edema, hematuria, oliguria, and hypertension

MEASUREMENT OF URINARY PROTEIN Urine dipstick

Measures albumin concentration via a colorimetric reaction between albumin and tetrabromophenol blue producing different shades of green according to the concentration of albumin in the sample

Negative Trace — between 15 and 30 mg/dL 1+ — between 30 and 100 mg/dL 2+ — between 100 and 300 mg/dL 3+ — between 300 and 1000 mg/dL 4+ — >1000 mg/dL

MEASUREMENT OF URINARY PROTEIN Sulfosalicylic acid test

Detects all proteins in the urine including the low molecular weight proteins that are not detected by the dipstick

Performed by mixing one part urine supernatant (eg, 2.5 mL) with three parts 3 percent sulfosalicylic acid, followed by assessment of the degree of turbidity

MEASUREMENT OF URINARY PROTEIN Quantitative assessment

Children with persistent dipstick-positive proteinuria must undergo a quantitative measurement of protein excretion, most commonly on a timed 24-hour urine collection

In children: levels >100 mg/m2 per day (or 4 mg/m2 per hour) are abnormal

Proteinuria of greater than 40 mg/m2 per hour is considered heavy or in the nephrotic range

MEASUREMENT OF URINARY PROTEIN Quantitative assessment

Alternative method of quantitative assessment is measurement of the total protein/creatinine ratio (mg/mg) on a spot urine sample, preferably the first morning specimen

For children >2 yrs: normal value for this ratio is <0.2 mg protein/mg creatinine

For infants and children <2yrs: <0.5 mg protein/mg creatinine

CAUSES OF ASYMPTOMATIC PROTEINURIA

TRANSIENT PROTEINURIA

Most common cause Can occur in association with fever,

seizures, strenuous exercise, emotional stress, hypovolemia, extreme cold, epinephrine administration, abdominal surgery, or congestive heart failure

Believed to be glomerular in origin, related to hemodynamic changes (decreased renal plasma flow) rather than altered permeability of capillary wall

ORTHOSTATIC PROTEINURIA Increase in protein excretion in the erect

position compared with levels measured during recumbency

Proteinuria usually does not exceed 1-1.5 gm/day

Mechanism postulated to involve an increased permeability of the glomerular capillary wall and a decrease in renal plasma flow

Long-term studies have documented the benign nature of this condition, with recorded normal renal function up to 50 years later

PERSISTENT PROTEINURIA

Present for long periods after initial detection

Absence of both orthostatic proteinuria and clinical evidence of renal disease

Clinical course may be benign May be secondary to parenchymal

disease

DIFFERENTIAL DIAGNOSES OF PERSISTENT PROTEINURIA Benign proteinuria Acute Glomerulonephritis, mild Chronic Glomerular Disease that can

lead to nephrotic syndrome Chronic nonspecific glomerulonephritis Chronic interstitial nephritis Congenital and acquired structural

abnormalities of urinary tract

EVALUATION OF ASYMPTOMATIC PROTEINURIA

HISTORY

Recent infection Weight changes Presence of edema Symptoms of hypertension Gross hematuria Changes in urine output Dysuria Skin lesions

HISTORY

Swollen joints Abdominal pain Previous abnormal urinalysis Growth history Medications

Family history Renal disease, hypertension, deafness,

visual disorders

PHYSICAL EXAMINATION

Vital signs Inspect for presence of edema, pallor,

skin lesions, skeletal deformities Screening for hearing and visual

abnormalities Abdominal exam Lung exam Cardiac exam

LABORATORY EVALUATION

TRANSIENT PROTEINURIA

Follow-up routinely Patient should have a repeat urinalysis

on a first morning void in one year

ORTHOSTATIC PROTEINURIA Perform Orthostatic Test CBC BUN Creatinine Electrolytes 24-hr urine excretion

< 1.5g/day repeat UA and blood work in 1 year

> 1.5g/day refer to Pediatric Nephrologist

Instructions for Testing for Orthostatic Proteinuria1. Patient voids at bedtime. Discard urine. No food or fluids

after dinner until the next morning. 2. When patient awakes in the morning, urine specimen is

collected prior to arising, or after as little ambulation as possible. Label specimen #1.

3. Child should ambulate for the next 2 to 3 hours. Then collect specimen. Label specimen #2.

4. Both specimens should be tested by dipstick or sulfosalicylic acid. Specimen #1 should be concentrated with a specific gravity of at least 1.018.

5. If specimen #1 is free of protein and specimen #2 has protein, then the test is positive for orthostatic proteinuria.

6. If both specimens have protein, orthostatic proteinuria is unlikely and further evaluation is necessary.

7. This protocol should be repeated on at least 2 occasions to confirm the diagnosis.

FURTHER EVALUATION OF PERSISTENT PROTEINURIA Examination or urine sediment CBC Renal function tests (blood urea nitrogen

and creatinine) Serum electrolytes Cholesterol Albumin and total protein

OTHER TESTS

Renal ultrasound Serum complement levels (C3 and C4) ANA Streptozyme testing, Hepatitis B and C serology HIV testing

PERSISTENT PROTEINURIA

If further work-up normal, urine dipstick should be repeated on at least two additional specimens. If these subsequent tests are negative for protein, the diagnosis is transient proteinuria.

If the proteinuria persists or if any of the studies are abnormal, the patient should be referred to a pediatric nephrologist

Urinary protein excretion should be quantified by a timed collection

INDICATIONS FOR RENAL BIOPSY Many nephrologists recommend close

monitoring for those children with urinary protein excretion below 500 mg/m2 per day before considering a biopsy

Monitoring should include assessment of blood pressure, protein excretion, and renal function. If any of these parameters shows evidence of progressive disease, a renal biopsy should be performed to establish a diagnosis.

MANAGEMENT

Avoid excessive restrictions in child’s lifestyle

Dietary protein supplementation is of no benefit

Salt restriction unnecessary and potentially dangerous

No indication for limitation of activity Importance of compliance with regular

follow-up should be stressed

REFERENCES

UpToDate Feld L, Schoeneman M, Kaskel F:

Evaluation of the Child with Asymptomatic Proteinuria. Pediatrics in Review 1984; 5: 248-254

Nelson’s Textbook of Pediatrics

QUESTIONS?