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Diagnosis of Urinary Tract Infection: Medical Imaging or Laboratory Based.

Byline: Najwa Farooq, Muhammad Shoaib, Quratul Ain, Zia ur Rehman Farooqi, Muhammad Javaid Asad and Adeeb Shahzad

Abstract

Urinary tract infection (UTI) affects women more than males mainly due to smaller urethra and feminine genital anatomy. Symptoms of UTI includes painful micturaition, flank pain, fever etc while its signs are pyuria, bacteriuria and tenderness in flank. In order to rule out UTI, laboratory tests are primarily performed, most important are urine routine examination, urine culture and sensitivity test. Radiological evaluation of urinary system is also done to determine the underlying causes of infection and the extent of damage caused to the renal system by the infection.

Key words: Drainage, UTI, Micturation, Pyelonephritis.

Introduction

Urinary tract infection (UTI) is a diverse condition ranging from mild cystitis to severe urosepsis leading to organ failure and death. The probability of UTI is high in females as compared to males because of the smaller urethral size. UTI is classified into 2 types i.e. lower UTI or cystitis and upper UTI or Pyelonephritis. The symptoms of former are fever and painful micturation while for later it is fever, flank tenderness and pain.1

UTI can be complicated or uncomplicated. Most common bacteria causing UTI include Escherichia Coli; transmitted from anus to the urethra.2 Other agents include: Pseudomonas aeruginosa, Mycobacterium tuberculosis, Staphylococcus aureus, Klebsiella pneumoniae, Enterococcus faecium,3 fungi and viruses.4

Risk factors of UTI include: female gender, family history, unhygienic sanitary condition, diabetes mellitus, uncircumcised and large prostate. Urinary catheters can also cause UTI.5

Pyelonephritis is a more complicated condition than cystitis. It can be caused from urinary tract obstruction especially at pelvi-ureteric junction, untreated cystitis and renal abscess.1

Untreated pyelonephritis can cause severe damage to the kidney resulting in emphysematous pyelonephritis. Treatment of upper and lower UTI includes administration of broad spectrum antibiotics and analgesics/ antipyretics. Oral or intravenous (IV) surgical intervention is required if there is urinary tract obstruction, abscess or emphysema.6

Medical imaging (MI) is a very basic diagnostic procedure in which visual representation of body's internal structure is produced utilizing X-rays, along with ultrasonic frequencies, radiofrequencies and -radiations.7-9 Radio frequencies are utilized in magnetic resonance imaging.10 -radiations are utilized in nuclear medicine primarily to access the function of an organ.11

UTI, particularly pyelonephritis, is mostly caused by an obstruction to the flow of the urine due to either calculus, tumor, stenosis or abscess/ cystitis. In order to detect these abnormalities, imaging studies are required.12

Imaging is performed for abnormalities requiring surgical intervention. For diagnosing acute papillary necrosis in children and in cases with rapidly deteriorating renal functions along with pyuria and bacteriuria.13

Commonly adopted methods for the diagnosis of Urinary Tract Infection (UTI) along with their pros and cons are compiled and a brief review is presented in this paper.

Table 1: Laboratory Methods for Detection of UTI.

###Laboratory Methods###Procedure###Advantages###Disadvantages

Non-###Bacteriuria Detection###Gram Staining of###Specimen is placed on###Simplest method.###Insensitive test.

culture###by Urine Microscopy###Un-centrifuged###the slide and is allowed###Provides immediate###Provides positive

methods###Bacteria###to dry.###information about the type###results only if the

###Dried specimen is gram###of infecting pathogen.###bacterial

###stained and is checked###concentration in the

###microscopically.###sample is more than

###105cfu/ml.

###Recommended not to

###be used in outpatient

###settings.

###Gram Staining of###Specimen is mixed and is###Pathogens and cells can be###Less specific.

###Centrifuged###placed in slide cytospin###separated and identified on

###Bacteria###centrifuge, gram stained###the basis of their structures.

###and then analyzed under###Sensitive test.

###microscope.

###Bacteriuria Detection by Nitrite Test###Biochemical reaction of###Very useful in detecting###Cannot identify

###converting nitrate in to###Enterobacteriacae.###pathogens associated

###nitrite by certain species###with urinary tract.

###of bacteria is detected

###chemically.

###Pyuria Detection by Urine Microscopy###Can be performed on###Leucocytes can be observed###Leucocyte count

###either centrifuged or un-###directly.###decreases rapidly if

###centrifuged gram stained###the urine is not fresh

###urine sample. Leucocytes###or is not preserved

###are counted through###properly.

###hemocytometer.

###Pyuria Detection by Leucocyte Esterase###Human leucocyte###Can yield positive test result###Can yield false

###Test###produce about ten###even if the sample is not###positive result when

###proteins which react with###preserved properly.###the urine sample gets

###ester substrate to produce###contaminated with

###alcohol, acid and colour###vaginal fluid.

###change proportional to###Low sensitivity.

###the amount of esterase in###Low specificity.

###the specimen.###Low positive

###predictive value with

###higher negative

###predictive value.

###Simultaneous Detection of Bacteriuria and###It involves tests for both###Both tests used together###Difficult to diagnose

###Pyuria###nitrate conversion and###give better results than if###smaller number of

###leucocyte esterase.###they are used alone.###bacteria.

###Very useful commercially.###Less sensitive.

###Higher specificity.###Abnormal urine

###colour which could

###be due to the use of

###certain drugs can

###affect the tests result.

Culture###Routine Bacterial Urine Culture: Important###Midstream clean catch###The causative organism is###Time consuming

methods###in patients with recurrent UTI, who are not###urine is collected.###identified.

###responding to the treatment or who have###Bacteria are allowed to###Antimicrobial sensitivity

###complicated UTI.###grow at 37AdegC for 48###test can be performed on it.

###hours.

###Sample is then examined

###under microscope.

Diagnosis of UTI is primarily laboratory based as shown in Table.14

Medical imaging is generally performed after clinical evaluation and laboratory findings. It is always indicated if renal calculi, cystitis, tumor, emphysematous pyelonephritis or abscess are suspected.15,16 The urine route examination (RE), ultrasound of urinary system and, plain radiography are followed by a computed tomography (CT) scan.

The most common findings in patients with UTI or pyelonephritis are hydronephrosis, renal calculus, pyonephrosis, renal abscess, renal cystitis, changes in renal parenchyma, change/reduction in kidney size, renal scares, emphysematous pyelonephritis and changes in renal function.17

The commonly performed imaging studies in case of UTI include plain radiography, intra venous urography, ultrasonography and computed tomography. Rarely Tc99m DTPA scan is performed to evaluate renal function which might have been severely affected by the infection.18

The advantages of plain radiography are that radio-opaque renal calculus or renal cystitis/ abscess can be ruled out. It can help in measuring the size of kidneys and can locate the position of calculus or presence of air in the urinary tract. Its disadvantage is radiation hazard.

The advantages of intravenous radiography are that the contrast media lines the renal tract and shows clearer image, it shows all the phases of excretion and post-voidal urine in the bladder and identifies any radio-lucent obstruction. Its disadvantages are radiation hazards, contrast reactions and contrast induced nephropathy.

The advantages of ultrasonography are that it has non ionizing radiation, therefore there are no radiation hazards. It can help in measuring the size of kidneys and extent of renal damage, it can detect renal calculus and its size, hydronephrosis and its extent, any dilatation of pelvicalyceal system, or renal cystitis, abscess, calculus and residual post-voidal urine in bladder or any changes in renal parenchyma. Its disadvantages are that sometimes it is difficult to position the patient, it is real time and operator dependent, full bladder is necessary for its evaluation and has a very low contrast resolution.

Computed tomography has advantages that size of kidneys, extent of renal damage, renal calculus and its size, hydronephrosis and its extent, renal cystitis and abscess, calculus and residual post-voidal urine in the bladder, renal parenchymal changes and renal tumor (benign or metastatic) can be assessed. It can help in differentiating between acute and chronic UTI. The disadvantages are that it has ionizing radiations, very high radiation dose is required and contrast hazards can occur if contrast is used.

In plain radiography, anteroposterior view of abdomen is taken either in supine or prone position.19

During intravenous urography, low osmolar iodinated contrast media is injected intravenously according to the patient's weight. Series of x-rays are taken after specific time intervals to trace excretion phases. It is used to assess any obstruction in the renal tract, either radiolucent or radio-opaque.20

Ultrasound of kidney, ureter and urinary bladder (KUB) is sometimes indicated as the first line diagnostic procedure in UTI after laboratory assessment. In ultrasonography, a curvilinear probe is placed on patient's abdomen, flank and suprapubic region where the transmitter transducer sends ultrasound frequencies of 3.5 - 5 MHz and images of kidneys and bladder are taken.21

In computed tomography, the patient lies on the couch and the couch is moved through the rotating gantry. Gantry is fixed with x-ray source and image receptor. The axial cut images of the patient's abdomen are obtained which traces the whole urinary tract system.22

UTI can cause severe damage to the renal system. Dysuria can result from UTI either pyelonephritis or cystitis. Imaging techniques help finding the underlying cause of UTI and proceed toward better medical and surgical intervention.

UTI can result in acute renal failure and chronic kidney disease, therefore any renal scarring or damage to the renal parenchyma can be assessed using imaging techniques. The stages of chronic kidney disease are evaluated on the basis of ultrasonography and not on the basis of CT as CT urogram can result in contrast induced nephropathy. Emphysematous pyelonephritis is caused by gas producing bacteria or fungi and often requires urgent medical or surgical intervention. It is practically impossible to assess gas in renal tract through lab based studies. For its diagnosis plain radiography is performed but reconstructed CT images shows better visualization of air in urinary tract.

Pus in urinary tract system or hydronephrosis proximal to the obstruction requires drainage of pus either percutaneously or by retrograde method. Ultrasound in such cases can estimate the extent of hydronephrosis and pyonephrosis. Imaging in the patients with UTI should be performed along with laboratory tests.

Conclusion

Several Laboratory methods are employed for the detection of UTI. A dipstick test is used for the simultaneous detection of bacteriuria and pyuria, If positive for nitrites with weakly positive for leukocytes (Pus cells), it suggests possible infection, but if it is positive for nitrites and strongly positive for leukocytes, it points towards UTI. When nitrites are found positive, a mid-stream urine sample should be sent for culture and sensitivity.

Radiological imaging in UTI can be used to detect underlying cause especially in patients having recurrent UTI and those with renal damage and deteriorating renal functions. Whenever radiological studies are performed, other than ultrasound, radiation exposure should be kept in mind.

Conflict of interest: None declared.

References

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Publication:Pakistan Journal of Medical Research
Article Type:Report
Date:Dec 31, 2017
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