Page 232 - Medicine and Surgery

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228 Chapter 6: Genitourinary system

accounts for half of the total protein excretion, occurs Prognosis
in orthostatic proteinuria, fever and exercise. Microalbuminuria (30–200 mcg albumin/24 h or an
early morning urine albumin:creatinine ratio >3) pre-
dicts mortality and renal failure in diabetes mellitus and
Clinical features
cardiovascular deaths in the elderly. It also occurs in
Proteinuria is usually asymptomatic, although heavy
hypertension, myocardial infarction and as part of the
proteinuria may be noticed as frothy urine, or if
acute phase response.
nephrotic syndrome develops. Protein excretion in-
creases in the upright position, and proteinuria, which
disappears on early morning collection before ambula- Imaging of the urinary tract
tion is called orthostatic proteinuria, a benign condi-
tion affecting 2–5% of adolescents, but uncommon over Plain X-ray of the kidneys, ureters and
the age of 30 years. If significant proteinuria is found, a bladder (KUB)
careful history and examination should be made to look On a plain X-ray radiopaque (calcium-containing, stru-
for an underlying cause, together with appropriate in- vite and cystine) stones and renal tissue calcification,
vestigations. calcification of vessels (e.g. an atheromatous aorta) and
calcification in tumours will show up. The outlines of the
kidneys are unreliably seen because of overlying bowel
Investigations
gas.
All positive urine dipstick measurement of protein
should be confirmed by laboratory testing. Dipstick de-
Renal ultrasound scan (USS)
tects albumin most sensitively, but false positives are
This is a useful imaging method of the kidneys. It avoids
caused by alkaline urine, antibiotics and X-ray contrast
the use of contrast dyes, which have to be given intra-
media. False negatives occur when there is proteinuria
venously, are nephrotoxic, and to which patients occa-
without much albuminuria, e.g. Bence Jones protein.
sionally develop an allergic reaction. USS is particularly
24-hour urinary protein should be quantified with
useful for the following:
a formal 24-hour urine collection, although this is be-
Renal obstruction, an important reversible cause of
ing superseded by spot urinary protein:creatinine ratios
renal failure. The pelvicalyceal systems and ureter(s)
(≤0.1 g = normal; 0.1–0.2 g = trace, 0.2–1.0 g = low-
look dilated except in early obstruction, or if the pa-
grade proteinuria, 1.0–3.0 g = moderate proteinuria,
tient is oligoanuric. Occasionally a cause is seen such
≥3.0 g = nephrotic range proteinuria).
as a stone.
Initial investigations include:
To assess the size of the kidneys. In renal failure, small
Urinalysis and microscopy to look for haematuria and

kidneys mean chronic renal failure, normal size kid-
evidence of urinary tract infection.
neys usually mean acute renal failure which is poten-
U&E’s, glucose to look for diabetes. Serum im-

tially reversible. The exceptions are diabetes mellitus,
munoglobulins and plasma protein electrophoresis.
amyloid and multiple myeloma.
Renal ultrasound.

Assessment of cysts and mass lesions.
Urine electrophoresis for Bence Jones protein or dif-

In refractory pyelonephritis to look for a renal abscess,
ferentiating glomerular (mainly albumin) from tubu-
obstruction or an underlying anatomical abnormality
lar loss (lighter chain proteins).
such as a stone.
Renal biopsy may be necessary to make a diagnosis.

For USS-guided kidney biopsy.
Doppler USS - to look for renal blood flow, renal vein

Management thrombosis and renal artery stenosis.
Depends on underlying cause and severity. Often mild
isolated proteinuria is treated expectantly after baseline Bladder and prostate USS
investigations (BP, U&Es, plasma creatinine) have been Bladder USS can assess residual volumes after bladder
done. emptying. Prostate USS is best done transrectally, and