Q3 Renal St George 2002



Q3 Renal St George 2002

An indigenous Australian man in a remote community is reviewed in a clinic. There is a high prevalence of renal disease in the community (30%). His BP is 150/90 and urine dipstick shows 1+ protein (specificity 85%; sensitivity 80%). The next most appropriate step is:

a) repeat early morning dipstick

b) urine microscopy

c) renal biopsy

d) 24 hour urine protein collection

e) creatinine/albumin urine ratio

Urine dipstick – The urine dipstick primarily detects albumin but is insensitive to the presence of light chains. This test is highly specific, but not very sensitive for the detection of proteinuria; it becomes positive only when protein excretion exceeds 300 to 500 mg/day. Thus, the urine dipstick is an insensitive method to detect microalbuminuria, the earliest clinical manifestation of diabetic nephropathy. In this setting, the development of a positive dipstick is a relatively late event, occurring at a time when there is already substantial structural injury. In nondiabetics, the presence of microalbuminuria is associated with cardiovascular disease.

The semi quantitative categories on the dipstick should be used with caution and only as a rough guide since urine concentration will affect the measurement. Dilute urine, for example, will underestimate the degree of proteinuria. False-positive results are common with many iodinated radiocontrast agents. Thus, the urine should not be tested for protein with the dipstick for at least 24 hours after a contrast study.

Measurement of quantitative urinary protein excretion – Most patients with persistent proteinuria should undergo a quantitative measurement of protein excretion. This can be accomplished by a 24-hour urine measurement; however, collecting these specimens may be cumbersome in ambulatory care settings.

An alternative method using a random urine specimen has been described. This test calculates the total protein-to-creatinine ratio (mg/mg).

APPROACH TO THE PATIENT WITH PROTEINURIA – The algorithm in Figure 2 demonstrates a useful clinical approach to the patient with proteinuria. It begins with a thorough history and physical examination. This may uncover a systemic or renal disease, such as diabetes mellitus, congestive heart failure, or autoimmune disease, that could account for the urine abnormality. In these cases, management of the proteinuria is part of the management of the underlying condition.

Examination of the urine – Examination of the urine is important in all patients with proteinuria.

• The urine sediment should be examined first, looking for other signs of glomerular disease such as hematuria, red cell casts, or lipiduria. Red-cell casts, for example, are pathognomonic for the presence of glomerular inflammation.

• If the sediment is unremarkable, the urine dipstick should be repeated on at least one other visit. If these subsequent tests are negative for protein, the likely diagnosis is transient proteinuria that may be due to stress, such as fever or heavy exercise. These patients need no further evaluation and should be reassured that they do not have renal disease.

A more thorough evaluation is warranted when proteinuria persists with a normal urine sediment. Renal function tests (BUN, creatinine) should be ordered, as well as a quantitative measurement of urine protein.

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