Proteinuria

Differential Overview

❑ Diabetes

❑ Drugs/toxins

❑ Acute tubular necrosis

❑ Glomerulonephritis

❑ Orthostatic

❑ Systemic lupus erythematosus

❑ Toxemia

❑ Polycystic kidneys

❑ Interstitial nephritis

❑ Renal vein thrombosis

❑ Multiple myeloma

❑ Amyloidosis

Diagnostic Approach

Proteinuria may present on urinalysis or as edema caused by reduced oncotic pressure from serum albumin loss. The dipstick detects albumin in concentrations of 30 mg/dL (Sensitivity 70%, Specificity 92%, Likelihood ratio 8.8), or 300 to 500 mg of proteinuria per day. False positives may be seen with dehydration and hematuria, both of which can be detected with the dipstick (specific gravity and hemoglobin). False negatives can occur when the protein is a low molecular weight tubular protein (not albumin), e.g., immunoglobulin light chains in myeloma or beta-2 microglobulin. In nephrotic syndrome more than 3.5 grams per day of proteinuria occurs.

Systemic disease should be suspected in the presence of fever, rash, or arthritis.

Clinical Findings

Diabetes  Microalbuminuria is an early marker of nephropathy, and appears before the urine dipstick can detect proteinuria. Glycosuria is also present, but the diagnosis of diabetes is usually well established before this complication develops.

Drugs/toxins  Drugs such as nonsteroidal antiinflammatory agents, chronic acetaminophen, contrast media, angiotensin-converting enzyme inhibitors, heroin, mercury, bismuth, gold, and penicillamine can all cause renal injury and proteinuria.

Acute tubular necrosis  Tubular proteinuria occurs with acute illness, especially with hypotension. “Dirty” casts can be seen on urinalysis.

Glomerulonephritis  The urine sediment will show red cells or red cell casts. Marked proteinuria is usually caused by glomerular injury. Membranous glomerulonephritis is the most common cause.

Orthostatic  Transient orthostatic or exercise-induced proteinuria is benign, and it may be demonstrated to be evanescent by changes in position (specimens on first arising vs. 2 hours later) or testing before and after exertion.

Systemic lupus erythematosus  Microscopic hematuria, malar-distribution rash, arthritis, and Raynaud phenomenon are clues.

Toxemia  Typically occurring in the third trimester in a primigravida, it is manifest with proteinuria, accelerated hypertension, and edema.

Polycystic kidneys  The onset is in the third or fourth decade, with hypertension, flank pain, hematuria, and a palpable lumpy kidney. There is often a history of renal stones.

Interstitial nephritis  There will be hematuria, fever, and a maculopapular rash, usually associated with the use of antibiotics, especially methicillin. Urinary eosinophils are occasionally found.

Renal vein thrombosis  Its appearance is suggested by acute flank pain, hematuria, and the sudden appearance of a left varicocele.

Multiple myeloma  The dipstick will be negative or weakly positive. Bone pain, particularly in the back or ribs, is a common presentation.

Amyloidosis  If occurring in the absence of systemic disease, an enlarged palpable kidney and a benign sediment may be the only clues. Systemic disease is most often marked by neuropathy, macroglossia, and waxy hemorrhagic periorbital plaques.

Book Source Details

• Book Title: Field Guide to Bedside Diagnosis
• Author(s): David S. Smith
• Year of Publication: 2007
• Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: Field Guide to Bedside Diagnosis Authors: David S. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-78178-165-5

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