Investigations of the Urinary Tract
Urine Examination
Urinalysis can be accorded the status of “liquid renal biopsy.” It gives many clues to diseases affecting the urinary tract.
Table of Contents
Specific gravity: It varies from 1.005 to 1.040 according to the patient’s state of hydration. In chronic renal failure, the concentrating ability of the kidneys is lost, and the specific gravity remains fixed at 1.010. This is called isosthenuria.
Read And Learn More: Surgery of Urology Notes
pH: The urinary pH normally ranges from 4.5 to 8. It varies depending on serum pH. Urine pH influences the type of stone formed (e.g. alkaline urine—infection by urea-splitting organisms resulting in infection stones, acidic urine—uric acid and cystine stones). Normally, urine is devoid of blood, protein, and sugar.
Proteinuria: It is defined as protein excretion >150 mg/ day. Protein, especially albumin, appears in urine following exercise, glomerulonephritis, and nephrotic syndrome.
Sugar: It appears in urine in diabetes mellitus. Transient postprandial glycosuria may be seen when serum glucose levels exceed the renal threshold.
Blood: This is seen as the presence of red blood cells (RBCs) in urine. The presence of >3 RBCs/hpf is considered significant. In haematuria, urine will be reddish, while in haemoglobinuria and myoglobinuria, urine will be brownish-black.
The causes of haematuria may be glomerular or nonglomerular. Glomerular causes are nephritis, analgesic nephropathy, IgA nephropathy, and connective tissue disorders. Non-glomerular causes are stones or tumours that involve the urinary tract (e.g. renal cell carcinoma, urothelial carcinomas).
Ketones: Ketone bodies, namely acetoacetic acid, beta hydroxy butyric acid, and acetone are seen in the urine in cases of diabetic ketoacidosis, starvation, and pregnancy.
White blood cells (WBCs): The presence of WBCs in the urine is called pyuria (>5 cells/hpf). Causes include urinary tract infection, stones, glomerulonephritis, foreign bodies, tuberculosis (sterile pyuria), and malignancies (sterile pyuria). In practice, the most common cause of sterile pyuria is unconfirmed infection treated empirically with antibiotics.
Casts and Crystals:
Casts: Tamm-Horsfall protein is a mucoprotein from renal tubular cells. It forms the nucleus of all casts by entrapping RBC/WBC/epithelial cells. Hyaline casts do not have cells and are normal.
Crystals: Different types of crystals are formed in acidic and alkaline urine and act as precursors for stone formation. Calcium phosphate and struvite crystals form in alkaline urine. Calcium oxalate, uric acid, and cystine crystals form in acidic urine. While most of the crystals mentioned here can be seen in normal subjects, cystine crystals (hexagonal or benzene ring-shaped) are truly pathological.
Urine Cytology:
Urine cytology refers to the microscopic examination of urinary samples for exfoliated cellular elements. For enhancing diagnostic yield, freshly voided specimens are essential. If positive, it indicates transitional cell carcinoma of bladder. Cytology is not useful for detecting other types of carcinoma, such as squamous cell or adenocarcinoma
24-hour Urinary Studies:
These are indicated for the metabolic evaluation of stone disease (identifies various abnormalities of electrolyte homeostasis) and the evaluation of recurrent pyelonephritis in children and diabetic nephropathy (degree of proteinuria).
Blood Tests
- Prostatic surface antigen (PSA): A glycoprotein that liquefies semen, an essential step in reproduction, is elevated in prostatic diseases. Its estimation is used to screen for carcinoma prostate but is not specific for this condition. Normal levels are 0–4 ng/ml. Carcinoma should be suspected if levels exceed 4 ng/ml.
- Testicular tumour markers:
- Alpha-fetoprotein (AFP): Elevated in embryonal carcinoma, yolk sac tumour.
- β-human chorionic gonadotrophin (β-hCG): Very high levels in choriocarcinoma.
- Lactate dehydrogenase (LDH): Elevated in embryonal carcinoma and seminoma indicates the bulk of the disease or tumour burden.
- Sex hormones: Hormonal assays are useful in specific situations. Pre- and post-treatment estimation of serum testosterone is useful when androgen deprivation is used to treat prostatic cancer. Similarly, a rise in serum androgens is seen in boys with precocious puberty due to Leydig cell tumors.
X-Ray Kub (Kidney, Ureter, Bladder)
- Plain X-ray KUB is a baseline investigation in suspected cases of calculous disease. The majority of urinary stones are radio-opaque, which facilitates their visibility on a plain X-ray.
- It should be taken in the supine position and cover the pubic symphysis and lower two ribs.
- Patients should take a fat-free, low residue diet, dimol 2 tablets, or any suitable anti-flatulence medication 3 times daily for 2–3 days prior to the X-ray.
- Stones appear as a white shadow when radio-opaque, and depending on the calcium content, the higher the calcium, the denser is the shadow!.
Imaging
Physical findings are often meagre in afflictions of the urinary tract; hence, imaging is relied on. Advances in imaging technology today have made renal imaging the most important part of urinary tract investigations. Some important investigations are given below.
Iodinated Contrasts:
Ionic: Diatrizoate, metrizoate, ioxaglate (more side effects, cheaper).
Nonionic: Iopamidol, iopromide (fewer side effects, costly).
Intravenous Pyelography (Ivp) And Intravenous Urogram (Ivu)
Aim:
- To study renal function
- To detect any pathology in the kidneys, ureters, and bladder
- To study any anatomical variations of the renal system.
Procedure:
- A fat-free, non-residue diet is given for 2–3 days prior to the procedure to avoid intestinal gas shadows.
- Dimol 2 tablets, 3 times daily for 2–3 days prior to the procedure to expel the gas.
- The patient should not take oral fluids 6 hours before the procedure.
- Radiological contrast dye: 45% sodium diatrizoate, 20–40 ml is injected through the median cubital vein.
Requirements before IVP:
1. Normal renal function is a prerequisite for IVU. Serum creatinine is reliable, but not urea because of variations in urea levels based on hydration. The normal value of serum creatinine is 0.5–2 mg%.
2. Plain X-ray KUB region to look for a renal stone— 90% of renal stones are radio-opaque (only 10% of gallstones are radio-opaque).
To distinguish between renal stones and gallstones on plain abdominal X-ray, take lateral film. Opacities anterior to the vertebral column are gallstones, and those overlying the spine are renal stones.
Precautions while Injecting the Dye Contrast Medium:
- The dye should be given very slowly.
- The dye should not extravasate.
- If bronchospasm occurs, hydrocortisone 100 mg and an antihistaminic should be administered IV in addition to inhalation of bronchodilator.
- In cases of urticaria and skin rashes, an antihistaminic should be given.
Radiography:
- Early films taken after 2 or 5 minutes demonstrate the kidney outline (nephrogram).
- 5 minutes later, pelvicalyceal system is visualised.
- 15–20 minutes later, the ureter and bladder can be visualise
- A post-voiding picture is taken to demonstrate any residual contrast in the urinary bladder. At times, a voiding phase is also included to study the urethra non-invasively. However, such a study is not useful to study vesicoureteral reflux, which calls for standard micturating cystourethrography (vide infra).
- Abdominal compression should be applied to better demonstrate pyelograms.
Contraindications for IVU:
- Idiosyncrasy to iodine: The test dose should be given beforehand.
- Renal failure: Kidneys fail to excrete the drug.
- Multiple myeloma: The contrast medium precipitates myeloma proteins, blocks the ureter and kidney, and causes anuria.
- Hyperuricaemia: Uric acid crystals deposit in the renal tubules.
- Sickle cell anaemia: Precipitates sickle cell crisis.
- Dehydration.
Uses of IVU:
- To diagnose congenital abnormalities, such as polycystic kidney, horseshoe kidney, single kidney, and duplication of kidneys and ureters.
- To diagnose hydronephrosis, hydroureter.
- To diagnose obstruction to the pelviureteric junction, ureters, primary obstructed megaureter.
- To diagnose renal, ureteric stones and bladder stones.
- To diagnose renal tuberculosis, tumours.
Intraoperative One-shot IV Pyelogram:
In ureteral injuries, when delayed contrast images are not possible because of haemodynamic instability, an intraoperative one-shot (2 mg/kg IV contrast material given 10 min before flat plate abdominal X-ray) IV pyelogram (IVP) is recommended for patients with hypotension or a history of significant deceleration, despite the absence of gross haematuria.
Retrograde Pyelography (RGP) Or Retrograde Ureterography (RGU)
Retrograde Pyelography Indications:
- When the kidney is not visualised by IVU
- Gross hydronephrosis
- Very high blood urea
- To selectively collect a urine sample from renal pelvis (e.g. renal tuberculosis)
- History of allergy to IV contrast materials. Caution should be exercised in such situations to avoid intravasation of contrast by forcible injection, which may precipitate an allergic reaction and rarely cause fatality.
- Prior to ureteroscopy.
Retrograde Pyelography Procedure:
- A cystoscopy is performed first.
- Ureteric orifices are identified and cannulated by a flexible catheter, which is introduced up to the pelvis of the kidney, and the contrast medium is injecte X-rays are taken at 5 minutes, 15 minutes, and 30 minutes.
Retrograde Pyelography Uses:
- Anatomical evaluation of the pelvicalyceal system.
- Early diagnosis of renal tuberculosis.
- Since the contrast medium is injected directly into the pelvis, the pelvicalyceal system can be identified better, helping to diagnose early transitional cell carcinoma of kidney.
Complications of RGP:
- It is an invasive procedure; hence, urinary tract infection can occur. Prophylactic antibiotics are given prior to the procedure.
- Chances of bladder or ureter perforation are rare. Retrograde ureteropyelogram using a bulb-tipped ureteric catheter lodged in the ureteric orifice eliminates the risk of inadvertent injuries due to retrograde catheterisation of the ureter.
Renal Arteriography Angiography
Renal Arteriography Angiography Technique:
The technique used now is digital subtraction angiography (DSA).
There are two methods:
- Retrograde arteriography using Seldinger technique. Selective renal angiography can be performed using a catheter over a guidewire passed into renal artery.
- Translumbar aortography wherein the aorta is punctured with a needle from behind, above the renal arteries, at the level of 1st lumbar vertebra.
Renal Arteriography Angiography Dose:
For aortography, 30 ml of contrast (hypaque), and for selective renal angiography, 6–8 ml are used.
Renal Arteriography Angiography Uses:
- To demonstrate pathological anatomy of the renal artery when renal artery stenosis or aneurysm is suspected.
- In renal cell carcinoma, tumour vascularity and extension of the tumour into the renal vein can be diagnosed during the venous phase.
- Bleeding from the kidney due to trauma, postpercutaneous nephrolithotomy (PCNL) bleeding, or arteriovenous malformation.
- Therapeutic application:
- Transluminal angioplasty can be done by inflating the balloon in cases of renal artery stenosis.
- Embolization of bleeding vessels, aneurysms.
Micturating Cystorerhrography(MCU)
In this procedure, the contrast medium is injected into the urinary bladder via an indwelling catheter, and X-rays are taken when the patient passes urine.
Micturating Cystorerhrography Indications:
- In children, to demonstrate vesicoureteric reflux
- Posterior urethral valve
- Vesical trauma
- Vesicovaginal or vesicocolic fistula.
Micturating Cystorerhrography Procedure:
A catheter is passed into the urinary bladder, and the dye is injecteThe catheter is removed, and the child is screened for vesicoureteric reflux during voiding of urine.
Films:
Filling phase, full bladder, voiding, and post-voiding phase films are taken.
Newer:
Direct or indirect radionuclide cystography using isotopes, which can even pick up minute reflux.
Micturating Cystorerhrography Complications:
Due to the invasive nature of the procedure, urinary tract infection may occur. Hence, prophylactic antibiotics should be used.
Ascending Urethrography (ASU) Or Retrograde Urethrography (RUG)
Urethrography is used in the diagnosis of urethral stricture, to know the length of stricture, proximal dilatation, or diverticulum.
Micturating Cystorerhrography Indications:
- Evaluation of urethral injury
- Investigation of urethral stricture
Contraindication:
Urethral haemorrhage, active urethral bleeding.
Precaution:
Barium and medium-containing oil such as lipiodol should not be used due to the risk of oil embolism with a urethral mucosal tear or breach. Conray 280 is injected slowly into the urethr acute settings, RGU is best done under cine control by trickling the contrast in increments.
Ultrasonography (USG)
This is a non-invasive investigation, that uses ultrasonic waves (sound waves with frequency >20,000 Hz). These waves cannot be heard by the human ear but are reflected or absorbed by tissues to various degrees that help diagnose different conditions. Ultrasound can be used through different approaches:
- Transabdominal
- Transrectal
- Transvaginal (used mostly by gynaecologists).
Limitations of USG:
- Operator-dependent
- Air precludes adequate imaging: Bowel gas may prevent satisfactory imaging of the pancreas/ kidneys.
- Obesity: Poor visualisation.
Uses of USG:
- Fluid can be differentiated from solid tissue. Hence, cystic swellings can be made out.
- Stones can be diagnosed as hyperechoic lesions and postacoustic shadowing.
- In an enlarged kidney with a thick cortex, disruption of the echo architecture can be made out, as in hydronephrosis.
- Residual urine in the bladder can be identified, which may be an indication of an enlarged prostate.
- The volume of the prostate can be measured.
Ultrasonography has become the investigation of choice to diagnose foetal hydronephrosis due to various reasons. This is advantageous because the management of the disease-causing hydronephrosis can be planned at the early stage, thereby preventing damage to the kidney. Moreover, intrauterine interventions are also possible, if the need arises.
Computerised Tomography (CT) Scanning
- CT can be done with or without contrast.
- CT without contrast (plain CT) is the investigation of choice for evaluating renal/ureteric colic.
- A CT scan can visualise most urinary tract calculi, even radiolucent stones not seen on plain X-ray KUB or IVU. The rare exception is indinavir stones.
- Contrast CT gives information about kidney function, similar to IVU. However, unlike IVU, which gives information only about the renal parenchyma and collecting system, CT can provide valuable information about perinephric events (e.g. urinoma, abscess, lymph nodes compressing ureters causing hydronephrosis).
- CT angiography is replacing conventional angiography for the diagnostic evaluation of renal vascular anatomy.
- It is more useful than arteriography to assess and display images of the body at selected levels.
- To diagnose of kidney tumour and its extent, spread, and infiltration.
- To stage cancer of prostate, bladder, kidney, testicular tumours, and renal trauma
Radioisotope Scanning
Gamma camera screening following the injection of technetium 99m gives information about proximal tubular function. To assess differential renal functions, diethylenetriamine penta-acetic acid (99mTc DTPA) or dimercaptosuccinic acid (99mTc DMSA) is used, which is filtered and secreted into the tubular lumen.
99mTc DTPA: Diethylenetriaminepenta-Acetic Acid This scan is done to determine the relative functions of both kidneys; it also tells about the total GFR and what percentage of total GFR is contributed by each kidney.
A relative function of 45 ±2% is considered acceptable for each kidney. The main indication for DTPA is long-term hydronephrosis. Examples are newborns with antenatally diagnosed hydronephrosis, and children with posterior urethral valves, at This scan is also useful to assess the improvement in relative function of the kidney after surgery for the above conditions. The yield of the DTPA scan can be improved by injecting IV lasix.
This is known as diuretic renography and will unmask marginal pelviureteric junction obstruction.
99mTc DMSA: Dimercaptosuccinic Acid
It is primarily used for cortical imaging. It shows details of the renal parenchymIt is particularly useful when looking for segmental abnormalities of kidney (e.g. renal scarring secondary to conditions like chronic pyelonephritis and renal tumours).
Endoscopy
Cystourethroscopy: The bladder and urethral mucosa can be visualised.
- The procedure is done under surface anaesthesia.
- Preparation: The external genitalia are cleaned with soap solution or an antiseptic agent, and 1% lignocaine jelly is injected into urethra to provide lubrication and anaesthesiThis should be left in place for 10 minutes for its action.
Uses of Cystoscopy:
- Diagnosis of bladder cancer, papilloma, cystitis.
- Position and character of ureteric orifices—in tuberculosis involving the urinary bladder, the ureteric orifices are shifted upwards; gaping in golf hole ureter.
- Indigo carmine test: 7 ml of 0.4% dye is injected IV. Observe the ureteric orifice through the cystoscope. Unilateral delay in dye appearance suggests obstruction. If there is a bilateral delay, it indicates impaired renal function.
- As a preliminary step for RGP.
- To rule out bladder involvement in gynaecological cancer (e.g. cancer cervix).
- To remove bladder stones (cystolitholapaxy)
- For transurethral resection of bladder tumour in early bladder cancers.
Urethroscopy
It refers to the visualisation of the urethra by introducing a cystoscope.
Types of Urethroscopy:
- Anterior urethroscopy is done in urethral stricture or chronic urethritis. It can rule out strictures due to granuloma.
- Posterior urethroscopy: To visualise prostatic urethra and verumontanum
- Verumontanum is red in cystoprostatitis.
- In chronic prostatitis, prostatic ducts may be seen discharging pus.
- When the lateral lobes are enlarged, they bulge into the prostatic urethral lumen and occlude it in the midline. In trilobar enlargement, the median lobe can be made out at the bladder neck, which juts into the vesical lumen.
Magnetic Resonance (Mr) Urography
MRI of the genitourinary system is useful in many situations. It is more expensive compared to other investigations.
Uses of MR Urography:
- For accurate evaluation of the inferior vena cava, thrombus in renal cell carcinoma.
- Extrinsic causes of ureteric obstruction causing hydronephrosis (e.g. retroperitoneal fibrosis, pelvic tumours).
- MR urethrography for accurate delineation of urethral injuries.
- MR is a poor method for visualizing stones and calcification.
Investigations of the Urinary Tract Multiple-Choice Questions
Question 1. When do you say there is significant haematuria?
- Presence of >2 RBCs/hpf
- Presence of >3 RBCs/hpf
- Presence of >1 RBC/hpf
- Presence of RBCs in the urine
Answer: 2. Presence of >3 RBCs/hpf
Question 2. Which of the following can be detected by urine examination?
- Transitional cell carcinoma
- Squamous cell carcinoma
- Adenocarcinoma
- Adenosquamous cell carcinoma
Answer: 1. Transitional cell carcinoma
Question 3. When do you suspect carcinoma prostate?
- If the patient has urgency of micturition
- Rectal examination reveals grade 2 enlargement of prostate
- If PSA levels are > 4 ng/ml
- If the patient has recurrent urinary tract infection
Answer: 3. If PSA levels are > 4 ng/ml
Question 4. Spider leg deformity in intravenous pyelography (IVP) is a diagnostic sign of which disease?
- Hydronephrosis
- Polycystic kidney
- Horseshoe kidney
- Carcinoma kidney
Answer: 2. Polycystic kidney
Question 5. Which of the following is a contraindication for IVP?
- Staghorn calculi
- Renal tuberculosis
- Horseshoe kidney
- Multiple myeloma
Answer: 4. Multiple myeloma
Question 6. The following are the advantages of retrograde pyelography over IVP:
- A urine sample can be selectively collected from the renal pelvis
- This can be done when the kidney is not visualised by IVP
- Intravenous contrast need not be given
- It is an invasive procedure
Answer: 4. It is an invasive procedure
Question 7. The investigation of choice in foetal hydronephrosis is:
- CT scan
- MRI scan
- Ultrasound
- DTPA scan
Answer: 3. Ultrasound
Question 8. The investigation of choice for renal parenchymal/ cortical function or damage is:
- IVP
- Contrast-enhanced CT scan
- DTPA scan
- DMSA scan
Answer: 4. DMSA scan
Question 9. The investigation of choice for renal function/ drainage is:
- CT scan
- MRI scan
- DTPA scan
- DMSA scan
Answer: 3. DTPA scan
Question 10. Indigo carmine test is done to study:
- Ureteric obstruction
- Prostatic obstruction
- Urethral obstruction
- Renal obstruction
Answer: 1. Ureteric obstruction
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