Investigations
1st investigations to order
urinalysis
Test
A standard initial test for evaluation of the genitourinary system. Haematuria (81.8%) and bacteriuria (90.9%) are more frequent in patients with xanthogranulomatous pyelonephritis than in those with chronic pyelonephritis.[39]
Result
may be normal; dipstick positive for leukocytes, nitrites, blood; microscopic analysis positive for WBCs, red blood cells, or bacteria
renal function
Test
Serum creatinine levels reflect the severity of the renal impairment. Estimated GFR (eGFR) is not as good at measuring renal function as creatinine clearance in patients with relatively well-preserved renal function.[28]
Result
elevated creatinine; reduced eGFR and reduced creatinine clearance
urine culture
electrolyte panel
Test
Electrolyte imbalance may be evident.
Result
hyponatraemia; hyperkalaemia; acidosis
FBC
Test
Anaemia is a common finding in emphysematous pyelonephritis (EPN) and any chronic infection; leukocytosis is more common in acute exacerbations (e.g., sepsis).
Result
anaemia; leukocytosis
renal ultrasound
Test
Is non-invasive, rapid, portable, offers no exposure to contrast or radiation, and may be the most readily available imaging modality when quick diagnosis and treatment of potentially life-threatening infections are required.
It is an initial test to identify structural abnormalities of the renal tract, complications of the disease, or to identify predisposing factors. It is not usually indicated to follow up disease progression. It is only used to follow up progression of specific factors such as renal stones or obstruction.
Result
small, irregular, scarred kidneys with echogenic parenchyma (typical of chronic irreversible kidney disease); hydronephrosis, renal stones and peri-renal fluid collections
kidney-ureter-bladder (KUB) x-ray
Test
Less informative than a CT but useful baseline investigation.
Result
renal stones; small or large kidneys; air in renal collecting/parenchymal system
CT abdomen
Test
Useful to image abdominal, pelvic, and retroperitoneal problems; oral and intravenous contrast medium is used to delineate the intestines and vascular tree.
It is not usually indicated to follow up disease progression, although it maybe repeated if potentially progressive underlying aetiological factors are identified.
Result
obstruction; renal stones; intra- and peri-renal fluid or air collections; and any related anatomical damage or disease in the retroperitoneum or abdomen
Investigations to consider
MRI abdomen
Test
Useful in evaluating complex genitourinary anomalies.
Can evaluate GFR, renal transit time, and differential renal function.[42]
MRI is superior to nuclear scintigraphy for diagnosis of pyelonephritis and renal scarring.[42]
Also used in follow-up of disease progression.
Result
obstruction; renal stones; intra- and peri-renal fluid, or air collections; and any related anatomical damage or disease in the retroperitoneum or abdomen
voiding cystourethrography (VCUG)
Test
VCUG is used to diagnose anatomical urinary tract abnormalities, such as posterior urethral valves and bladder outlet obstruction, which may predispose patients to vesicoureteral reflux and recurrent pyelonephritis.
Comprehensive urological imaging protocols, including renal ultrasonography, cortical renal scintigraphy, and VCUG, have been proposed to diagnose vesicoureteral reflux.[43]
Result
may demonstrate reflux
renal biopsy
Test
In most patients, renal damage occurs slowly over a long period of time in response to a chronic inflammatory process or infections. This results in thinning of the renal cortex along with deep, segmental, coarse cortical scarring. Club-shaped deformity of the renal calyces occurs as the papilla(e) retract into the scar(s). One scar or several may be present, in one or both kidneys. Most scars develop in the upper and lower poles because of the frequency of reflux in these sites.[20]
For those patients who are asymptomatic, without significant past medical history and with abnormalities detected on laboratory tests or imaging, a biopsy may be warranted to look for treatable causes of renal disease. However, a renal biopsy is almost never used any more to make the diagnosis of chronic pyelonephritis, as imaging techniques have improved considerably and results of the biopsy do not alter treatment.
Result
parenchyma within the scarred areas often contains atrophic tubules with no glomeruli; uninvolved tissue may be locally hypertrophied, with segmental involvement
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