Proteinuria Evaluation
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Proteinuria
Usually dipstick-positive. Recall, though, that the dipstick detects only albumin. If there is any reason to suspect proteinuria and the dipstick is negative, confirm UA with sulfosalicylic acid (SSA), as this detects both albumin and nonalbumin proteins.Classifications: Transient, Orthostatic, Persistent
Transient
Transient Idiopathic: Usually seen in children, adolescents, and young adults who are otherwise asymptomatic and healthy, and whose urinalysis shows no other abnormalities. Repeat test 2-3 times to confirm not persistent.Intermittent Idiopathic: Proteinuria present in ~50% of urine samples tested for any individual in the absence of orthostasis or another attributable etiology. Usually occurs in those <30 years old and long term prognosis is favorable. Yearly monitoring is recommended.
Functional: Occurs without evidence of intrinsic renal disease in the face of acute illness, some chronic conditions, or stressful events such as fever, CHF, exercise, seizures, pregnancy, OSA.
Orthostatic
Increased proteinuria while upright with normal amounts while supine. Present in up to 3-5 % of adolescents and young men; uncommon in patients >30 years old. Long-term follow-up shows no deterioration of renal function with spontaneous resolution in 50% of patients 10 years after diagnosis. Do split 24 hour urine collection to diagnose.
Persistent
Persistent Isolated: Proteinuria that persists at < 3.5 g/24h/1.73 m2 in the absence of other renal or systemic disease. Patients should be followed closely and referred to nephrologist for any change in urinary sediment, worsening proteinuria, or onset of renal insufficiency. Renal biopsy probably indicated.Persistent Proteinuria with Systemic or Other Renal Disease:
Glomerular: Heavy or nephrotic range proteinuria (>3.5 g/24h/1.73 m2.
Tubular: Disease of the tubular epithelium causing inability to reabsorb filtered low-molecular-weight (LMW) proteins (e.g., beta-2 microglobulin or lysozyme). Usually <2 g/24h/1.73 m2.
Overflow: LMW protein overproduced in the body, filters across the glomerulus in amounts too great for the reabsorptive capacity of the tubules. Most often this is Ig light chain excretion in conditions like multiple myeloma or amyloidosis. Lysozymuria can occur in acute monocytic leukemia.
