A 17-year-old boy is evaluated for abnormal urinalysis findings. He came to the clinic 2 weeks ago with low back pain, and a urinalysis at that time showed 2+ protein. He currently feels fine and has no urinary complaints. The patient has not exercised vigorously or taken any medications. He has no other medical problems and received all appropriate childhood vaccinations. He does not use tobacco or illicit drugs. The patient is not sexually active. His father had early coronary disease and a stroke. His blood pressure is 112/70 mm Hg and pulse is 77/min. BMI is 24 kg/m². Physical examination shows no abnormalities. Laboratory results from this visit are as follows: Urine sediment microscopy is unremarkable for casts. A 24-hour urine collection shows 600 mg of protein (normal <150 mg) .
Which of the following is the best next step in management of this patient?

Question

A 17-year-old boy is evaluated for abnormal urinalysis findings. He came to the clinic 2 weeks ago with low back pain, and a urinalysis at that time showed 2+ protein. He currently feels fine and has no urinary complaints. The patient has not exercised vigorously or taken any medications. He has no other medical problems and received all appropriate childhood vaccinations. He does not use tobacco or illicit drugs. The patient is not sexually active. His father had early coronary disease and a stroke. His blood pressure is 112/70 mm Hg and pulse is 77/min. BMI is 24 kg/m². Physical examination shows no abnormalities. Laboratory results from this visit are as follows:

Urine sediment microscopy is unremarkable for casts. A 24-hour urine collection shows 600 mg of protein (normal <150 mg) .
Which of the following is the best next step in management of this patient?

Quizplus · Accepted Answer

Explanation: This patient's isolated proteinuria on urinalysis is consistent with orthostatic proteinuria, a higher than normal protein excretion during the day (when upright) but normal protein excretion at night (when supine). Orthostatic proteinuria is the most common cause of proteinuria in adolescents (60%-75% prevalence) and rarely occurs after age 30. Possible mechanisms of proteinuria include an exaggerated normal response to upright posture, increased glomerular capillary pressure due to an exaggerated angiotensin II response with standing, subtle glomerular abnormality (eg, focal mesangial hypercellularity and/or basement membrane thickening), or left renal vein entrapment. Diagnosis can be confirmed by comparing the urine protein-to-creatine ratio in urine samples collected in both the supine and standing positions. Another confirmatory test is to compare protein excretion in a split 24-hour urine collection divided between the daytime (after morning void until bedtime) and nighttime periods. Orthostatic proteinuria is confirmed in patients with a significant elevation in daytime protein excretion but a normal nighttime rate. Clinical features suggesting an alternate diagnosis include history of nephrotoxic agents, acute glomerulonephritis (eg, hypertension, hematuria, acute kidney injury), or nephrotic syndrome (eg, proteinuria >3-3.5 g/24 hr, hypoalbuminemia, edema). (Choice A) Positive antinuclear antibody screen and low serum complements (C3 and C4) suggest lupus nephritis in patients with acute glomerulonephritis. However, this patient has no findings of lupus (eg, malar rash, arthritis) or acute glomerulonephritis. (Choice B) CT scan of the abdomen with intravenous contrast can evaluate for malignancy in patients with renal masses or hematuria. However, it is not as useful for evaluating proteinuria. (Choice D) Ultrasound-guided kidney biopsy may be required if this patient has persistent proteinuria or other renal abnormalities (eg, hematuria, hypertension, peripheral edema). (Choice E) Urine protein electrophoresis can detect monoclonal light chains or immunoglobulins in conditions such as multiple myeloma, which is more common in older adults and is rare in young adults. Educational objective: Orthostatic proteinuria is the most common cause of proteinuria in adolescents. The degree of proteinuria is mild and other significant renal abnormalities (eg, hematuria, acute kidney injury, hypertension) are absent. Orthostatic proteinuria can be diagnosed by split (day and night) 24-hour urine collection showing elevated daytime but normal nighttime protein excretion rates. References: Mechanisms of orthostatic proteinuria: lessons from a transplant donor. (http://www.ncbi.nlm.nih.gov/pubmed/8400067) Orthostatic proteinuria and the spectrum of diurnal variability of urinary protein excretion in healthy children. (http://www.ncbi.nlm.nih.gov/pubmed/20165888)

A 17-Year-Old Boy Is Evaluated for Abnormal Urinalysis Findings