Urinary tract infections in children US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Urinary tract infections in children. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Urinary tract infections in children US Medical PG Question 1: A 62-year-old man comes to the physician because of a 2-day history of fever, chills, and flank pain. Five days ago, he was catheterized for acute urinary retention. His temperature is 39.3°C (102.7°F). Physical examination shows right-sided costovertebral angle tenderness. Urine studies show numerous bacteria and WBC casts. Urine culture on blood agar grows mucoid, gray-white colonies. Urine culture on eosin methylene blue agar grows purple colonies with no metallic green sheen. Which of the following is the most likely causal pathogen?
- A. Escherichia coli
- B. Klebsiella pneumoniae (Correct Answer)
- C. Pseudomonas aeruginosa
- D. Proteus mirabilis
- E. Staphylococcus saprophyticus
Urinary tract infections in children Explanation: ***Klebsiella pneumoniae***
- The presence of **mucoid, gray-white colonies** on blood agar and **purple colonies with no metallic green sheen** on EMB agar, along with a history of catheterization, fever, and flank pain strongly suggests *Klebsiella pneumoniae*.
- *Klebsiella* is a common cause of **catheter-associated UTIs** and often produces mucoid colonies due to its capsule.
*Escherichia coli*
- *E. coli* typically produces **metallic green sheen** on EMB agar due to rapid lactose fermentation, which is absent in this case.
- While *E. coli* is a common cause of UTIs, the specific culture findings differentiate it from *Klebsiella*.
*Pseudomonas aeruginosa*
- *Pseudomonas* often produces a **grape-like odor** and distinctive **blue-green pigment** on agar, neither of which is mentioned.
- It does not ferment lactose and would thus not produce purple colonies on EMB, but rather appear as colorless or clear colonies.
*Proteus mirabilis*
- *Proteus mirabilis* is known for its **swarming motility** on agar, which creates a characteristic spreading growth pattern, not merely mucoid colonies.
- It also produces **urease**, which can lead to alkaline urine and struvite stones, but the distinguishing colony morphology is not met.
*Staphylococcus saprophyticus*
- *Staphylococcus saprophyticus* is a **Gram-positive coccus** and would not grow purple colonies on EMB agar, which is selective for Gram-negative bacteria.
- It is a common cause of UTIs in young, sexually active women, which does not fit the patient's demographic.
Urinary tract infections in children US Medical PG Question 2: A 76-year-old woman presents to the primary care physician for a regular check-up. History reveals that she has had episodes of mild urinary incontinence over the past 2 years precipitated by sneezing or laughing. However, over the past week, her urinary incontinence has occurred during regular activities. Her blood pressure is 140/90 mm Hg, heart rate is 86/min, respiratory rate is 22/min, and temperature is 37.7°C (99.9°F). Physical examination is remarkable for suprapubic tenderness. Urinalysis reveals 15 WBCs/HPF, positive nitrites, and positive leukocyte esterase. Which of the following is the best next step for this patient?
- A. Pelvic floor muscle training
- B. Ultrasound scan of the kidneys, urinary tract, and bladder
- C. Cystoscopy
- D. Urine culture (Correct Answer)
- E. Start empirical antibiotic therapy
Urinary tract infections in children Explanation: ***Urine culture***
- The patient presents with classic **signs of a urinary tract infection (UTI)**: new onset urinary incontinence worsening, suprapubic tenderness, and urinalysis positive for **WBCs, nitrites, and leukocyte esterase**.
- A urine culture is essential to **confirm the diagnosis of UTI**, identify the causative organism, and determine antibiotic sensitivity before initiating targeted treatment.
*Pelvic floor muscle training*
- This intervention is appropriate for **stress urinary incontinence (SUI)**, which the patient initially experienced, but it will not address the acute infection.
- While it may be considered after UTI treatment for managing chronic incontinence, it's NOT the immediate priority given the acute infectious symptoms.
*Ultrasound scan of the kidneys, urinary tract, and bladder*
- An ultrasound might be considered if there were concerns for **obstruction**, **pyelonephritis**, or recurrent UTIs after treatment, but it is not the immediate diagnostic step for an acute, uncomplicated UTI.
- The primary goal is to identify and treat the infection first.
*Cystoscopy*
- **Cystoscopy** is an invasive procedure generally reserved for investigating causes of recurrent UTIs, hematuria, or bladder abnormalities after initial treatment failures or in specific clinical scenarios, not for initial diagnosis of an apparent UTI.
- It would be premature and unnecessary at this stage without ruling out a simple infection.
*Start empirical antibiotic therapy*
- While antibiotics are indeed needed, starting empirical therapy without a culture could lead to **antibiotic resistance** or ineffective treatment if the causative organism is not susceptible to the chosen antibiotic.
- Given the suprapubic tenderness and urinalysis findings, a UTI is highly likely, but **culture and sensitivity guided therapy** is the best practice for optimal patient outcomes and to prevent resistance, especially in an elderly patient.
Urinary tract infections in children US Medical PG Question 3: A 9-year-old boy is brought to the emergency department by his mother. She says that he started having “a cold” yesterday, with cough and runny nose. This morning, he was complaining of discomfort with urination. His mother became extremely concerned when he passed bright-red urine with an apparent blood clot. The boy is otherwise healthy. Which of the following is the most likely underlying cause?
- A. BK virus infection
- B. E. coli infection
- C. CMV infection
- D. Adenovirus infection (Correct Answer)
- E. Toxin exposure
Urinary tract infections in children Explanation: ***Adenovirus infection***
- **Adenovirus** is a common cause of **hemorrhagic cystitis** in children, often following a mild upper respiratory tract infection.
- Symptoms like **dysuria**, **hematuria** with blood clots, and a preceding "cold" are classic presentations of adenovirus-induced cystitis.
*BK virus infection*
- **BK virus** is typically associated with **hemorrhagic cystitis** in **immunocompromised individuals**, particularly after bone marrow or kidney transplantation.
- The patient described is a healthy 9-year-old, making BK virus a less likely primary cause in this context.
*E. coli infection*
- **_E. coli_** is the most common cause of **urinary tract infections (UTIs)**, often presenting with dysuria, frequency, and urgency.
- While _E. coli_ can cause hematuria, the presence of **gross hematuria with blood clots** following a viral prodrome is more characteristic of viral hemorrhagic cystitis, especially due to adenovirus.
*CMV infection*
- **CMV (cytomegalovirus) infection** can cause various symptoms, but it is primarily known for causing serious disease in **immunocompromised individuals** or congenital infections.
- While CMV can rarely cause hemorrhagic cystitis, it is much less common than adenovirus in healthy children and not typically associated with the described acute presentation.
*Toxin exposure*
- **Toxin exposure**, such as certain chemicals or drugs (e.g., cyclophosphamide), can induce **hemorrhagic cystitis**.
- However, there is **no history of toxin exposure** in the clinical vignette, and the preceding "cold" symptoms strongly point towards an infectious cause.
Urinary tract infections in children US Medical PG Question 4: A 26-year-old female presents to her primary care physician concerned that she has contracted a sexually transmitted disease. She states that she is having severe pain whenever she urinates and seems to be urinating more frequently than normal. She reports that her symptoms started after she began having unprotected sexual intercourse with 1 partner earlier this week. The physician obtains a urinalysis which demonstrates the following, SG: 1.010, Leukocyte esterase: Positive, Nitrites: Positive, Protein: Trace, pH: 5.0, RBC: Negative. A urease test is performed which is negative. This patient has most likely been infected with which of the following organisms?
- A. Enterobacter cloacae
- B. Staphylococcus saprophyticus
- C. Proteus mirabilis
- D. Klebsiella pneumoniae
- E. Escherichia coli (Correct Answer)
Urinary tract infections in children Explanation: ***Escherichia coli***
- The urinalysis findings of **positive leukocyte esterase**, **nitrites**, and **trace protein** with a slightly acidic pH (5.0) are highly suggestive of a **urinary tract infection (UTI)**.
- *E. coli* is the most common cause of UTIs, especially in young, sexually active women, and is typically **urease-negative**, consistent with the information provided.
- *E. coli* accounts for **80-90% of uncomplicated UTIs** and produces nitrites from dietary nitrates, making it the most likely pathogen in this clinical scenario.
*Enterobacter cloacae*
- While *Enterobacter cloacae* can cause UTIs, it is less common than *E. coli* in uncomplicated cases and is often associated with nosocomial infections or those in immunocompromised individuals.
- Its urease activity can vary, so a negative urease test doesn't rule it out completely but makes *E. coli* a more likely primary choice in this context.
*Staphylococcus saprophyticus*
- *S. saprophyticus* is a common cause of UTIs in young, sexually active women (second most common cause after *E. coli*) and is typically **urease-negative**, which is consistent with the negative test.
- However, the presence of **positive nitrites** points more strongly towards **Gram-negative bacteria** like *E. coli*, as *S. saprophyticus* is a **Gram-positive coccus** that does not produce nitrite reductase and therefore does not convert nitrates to nitrites.
*Proteus mirabilis*
- *Proteus mirabilis* is known for causing UTIs and is characteristically **urease-positive**, leading to alkaline urine (higher pH) and sometimes **struvite stones**.
- The **negative urease test** and acidic urine pH (5.0) in this case effectively rule out *Proteus mirabilis*.
*Klebsiella pneumoniae*
- *Klebsiella pneumoniae* can cause UTIs and is generally **urease-negative**, but it is less frequently the cause of uncomplicated UTIs compared to *E. coli*.
- Although it can produce nitrites, *E. coli* remains the most common etiology in this clinical scenario.
Urinary tract infections in children US Medical PG Question 5: A 28-year-old woman presents to the emergency department with fever, chills, nausea, vomiting, and right flank pain for 2 days. Temperature is 39.2°C (102.6°F), blood pressure is 95/60 mmHg, pulse is 110/min, and respirations are 18/min. She appears ill and is unable to tolerate oral fluids. Physical examination shows right costovertebral angle tenderness. Urinalysis shows:
Protein 1+
Leukocyte esterase positive
Nitrite positive
RBC 2/hpf
WBC 90/hpf
WBC casts numerous
Which of the following is the most appropriate next step in management?
- A. Treat on an outpatient basis with ciprofloxacin
- B. Wait for culture results and treat accordingly
- C. Treat on an outpatient basis with nitrofurantoin
- D. Admit the patient and perform a CT scan of the abdomen
- E. Admit the patient and treat with intravenous levofloxacin (Correct Answer)
Urinary tract infections in children Explanation: ***Admit the patient and treat with intravenous levofloxacin***
- The presence of **WBC casts** is pathognomonic for **pyelonephritis**, an upper urinary tract infection.
- Given the severity indicated by **WBC casts** and significant **leukocyturia** (WBC 90/hpf), **inpatient management** with **intravenous antibiotics** (like levofloxacin) is appropriate to prevent progression to urosepsis.
*Treat on an outpatient basis with ciprofloxacin*
- While ciprofloxacin is an effective antibiotic for UTIs, **outpatient treatment** is generally not recommended for **severe pyelonephritis**, especially when WBC casts are present.
- This approach carries a higher risk of treatment failure and complications like **urosepsis** in severe cases.
*Wait for culture results and treat accordingly*
- Delaying treatment until culture results are available is inappropriate in a patient with signs of **acute pyelonephritis** (WBC casts, positive nitrite/leukocyte esterase, significant WBCs).
- Prompt initiation of **empiric antibiotics** is crucial to prevent rapid clinical deterioration and potential morbidity.
*Treat on an outpatient basis with nitrofurantoin*
- **Nitrofurantoin** primarily achieves therapeutic concentrations in the **lower urinary tract** and is not effective for treating **pyelonephritis** (upper UTI).
- Its use would lead to treatment failure and potential worsening of the infection due to inadequate drug delivery to the renal parenchyma.
*Admit the patient and perform a CT scan of the abdomen*
- While a **CT scan of the abdomen** may be considered later to evaluate for complications such as **abscess formation** or **obstruction**, the **immediate priority** is to initiate **antibiotic treatment** for acute pyelonephritis.
- Delaying antibiotic therapy in favor of imaging can lead to rapid clinical deterioration.
Urinary tract infections in children US Medical PG Question 6: A 1-year-old boy is brought to the physician because of irritability and poor feeding that began 2 days ago. His mother reports that he has been crying more than usual during this period. He refused to eat his breakfast that morning and has not taken in any food or water since that time. He has not vomited. When changing the boy's diapers this morning, the mother noticed his urine had a strong smell and pink color. He has not passed urine since then. He was born at term and has been healthy. He appears ill. His temperature is 36.8°C (98.2°F), pulse is 116/min, and blood pressure is 98/54 mm Hg. The boy cries when the lower abdomen is palpated. Which of the following is the most appropriate next step in management?
- A. Obtain clean catch urine sample
- B. Perform renal ultrasound
- C. Administer cefixime
- D. Perform transurethral catheterization (Correct Answer)
- E. Perform voiding cystourethrogram
Urinary tract infections in children Explanation: ***Perform transurethral catheterization***
- The child presents with symptoms suggestive of a **urinary tract infection (UTI)**, including irritability, poor feeding, strong-smelling urine, **pink-colored urine (hematuria)**, and abdominal pain. The combination of these findings in an acutely ill infant strongly indicates UTI with possible hemorrhagic cystitis.
- Given his age and inability to cooperate for a clean-catch sample, **transurethral catheterization** is the most reliable method to obtain an uncontaminated urine sample for culture and urinalysis in an acutely ill infant.
- This method provides a **sterile urine sample**, essential for accurate diagnosis (confirming pyuria, bacteriuria, and hematuria) and guiding appropriate treatment, as contamination rates are high with other collection methods in this age group.
*Obtain clean catch urine sample*
- While a clean catch urine sample is ideal for older children and adults, it is often **not feasible or reliable** in a 1-year-old due to difficulty in obtaining an uncontaminated specimen.
- Contamination rates for clean catch samples in infants can be very high, leading to **false positive results** and unnecessary antibiotic treatment.
*Perform renal ultrasound*
- A renal ultrasound is useful for identifying **structural abnormalities** in the urinary tract, which may predispose a child to UTIs. However, it is an imaging study, **not a diagnostic tool for acute infection**, and should be performed after a confirmed diagnosis of UTI, especially in recurrent cases.
- Imaging should be considered after the initial management step of **diagnosing the UTI** with a sterile urine sample, to investigate underlying causes.
*Administer cefixime*
- Administering antibiotics like cefixime is the treatment for a UTI, but it should only be done **after obtaining a urine sample for culture**. Starting antibiotics empirically without a confirmed diagnosis may lead to **antibiotic resistance** and makes it difficult to ascertain the causative organism if symptoms persist.
- The priority in this acute setting is to first **confirm the diagnosis of UTI** with a reliable urine culture, then choose appropriate antimicrobial therapy based on sensitivity or local resistance patterns.
*Perform voiding cystourethrogram*
- A **voiding cystourethrogram (VCUG)** is primarily used to diagnose **vesicoureteral reflux (VUR)**, a condition where urine flows backward from the bladder into the ureters. This is an advanced imaging study typically reserved for children with recurrent UTIs or those with a confirmed UTI and abnormal renal ultrasound findings, to investigate for reflux.
- It involves radiation exposure and catheterization and is **not an initial diagnostic step** for an acute UTI in a child who has not yet undergone initial workup. The immediate priority is to obtain a sterile urine sample to diagnose the current infection.
Urinary tract infections in children US Medical PG Question 7: A 22-month-old girl is brought to the emergency department with a 24-hour history of fever, irritability, and poor feeding. The patient never experienced such an episode in the past. She met the normal developmental milestones, and her vaccination history is up-to-date. She takes no medications, currently. Her temperature is 38.9°C (102.0°F). An abdominal examination reveals general tenderness without organomegaly. The remainder of the physical examination shows no abnormalities. Laboratory studies show the following results:
Urine
Blood 1+
WBC 10–15/hpf
Bacteria Many
Nitrite Positive
Urine culture from a midstream collection reveals 100,000 CFU/mL of Escherichia coli. Which of the following interventions is the most appropriate next step in evaluation?
- A. No further testing
- B. Voiding cystourethrography
- C. Renal and bladder ultrasonography (Correct Answer)
- D. Intravenous pyelography
- E. Dimercaptosuccinic acid renal scan
Urinary tract infections in children Explanation: ***Renal and bladder ultrasonography***
- For a febrile infant or young child (2 to 24 months) with a first **culture-proven urinary tract infection (UTI)**, renal and bladder ultrasonography is the recommended imaging study.
- This imaging is crucial to evaluate for **anatomic abnormalities** of the kidneys and urinary tract that could predispose to recurrent infections or renal damage.
- Current AAP guidelines recommend ultrasound as the **initial imaging modality** to assess for conditions like vesicoureteral reflux (VUR), hydronephrosis, or obstructive uropathy.
*No further testing*
- This option is incorrect because a **febrile UTI** in a young child warrants imaging to rule out **underlying genitourinary abnormalities** that could predispose to recurrent infections or renal damage.
- Skipping further evaluation could miss conditions like **vesicoureteral reflux (VUR)** or obstructive uropathy.
*Voiding cystourethrography*
- **Voiding cystourethrography (VCUG)** was historically recommended for all young children after a first UTI but is now reserved for specific situations, such as **abnormal renal/bladder ultrasound findings** or recurrent UTIs.
- VCUG involves radiation exposure and catheterization, making it less favorable as a first-line imaging study.
*Intravenous pyelography*
- **Intravenous pyelography (IVP)** involves intravenous contrast and radiation, making it an **invasive and high-radiation study** that has largely been replaced by ultrasound and CT for evaluating the urinary tract.
- It is not recommended as the initial imaging of choice for a child with a first UTI due to its **risks and availability of safer alternatives**.
*Dimercaptosuccinic acid renal scan*
- A **dimercaptosuccinic acid (DMSA) renal scan** is primarily used to detect **renal scarring** and assesses differential renal function.
- While it can be useful in identifying long-term consequences of UTIs, it is not the primary imaging study for initial evaluation of **ureteral or bladder abnormalities** in a first febrile UTI.
Urinary tract infections in children US Medical PG Question 8: A 23-year-old woman gravida 2, para 1 at 12 weeks' gestation comes to the physician for her initial prenatal visit. She feels well. She was treated for genital herpes one year ago and gonorrhea 3 months ago. Medications include folic acid and a multivitamin. Vital signs are within normal limits. Pelvic examination shows a uterus consistent in size with a 12-week gestation. Urine dipstick is positive for leukocyte esterase and nitrite. Urine culture shows E. coli (> 100,000 colony forming units/mL). Which of the following is the most appropriate next step in management?
- A. Perform cystoscopy
- B. Administer gentamicin
- C. Administer trimethoprim/sulfamethoxazole (TMP/SMX)
- D. Administer amoxicillin/clavulanate (Correct Answer)
- E. Perform renal ultrasound
Urinary tract infections in children Explanation: ***Administer amoxicillin/clavulanate***
- The patient has **asymptomatic bacteriuria** based on a positive urine dipstick for leukocyte esterase and nitrite and a urine culture showing *E. coli* (> 100,000 CFU/mL) in a pregnant patient.
- **Amoxicillin/clavulanate** is a safe and effective first-line antibiotic for treating asymptomatic bacteriuria in pregnancy due to its broad spectrum and safety profile for the fetus.
*Perform cystoscopy*
- **Cystoscopy** is an invasive procedure typically reserved for evaluating persistent hematuria, recurrent UTIs despite appropriate therapy, or suspected bladder pathology.
- It is not indicated for initial management of asymptomatic bacteriuria, especially in pregnancy, as it carries risks and offers no immediate therapeutic benefit for this condition.
*Administer gentamicin*
- **Gentamicin** is an aminoglycoside antibiotic that is generally **contraindicated in pregnancy** due to potential **fetal ototoxicity** and nephrotoxicity.
- While effective against *E. coli*, its risks outweigh the benefits for asymptomatic bacteriuria, especially when safer alternatives are available.
*Administer trimethoprim/sulfamethoxazole (TMP/SMX)*
- **Trimethoprim/sulfamethoxazole (TMP/SMX)** is generally **avoided in the first trimester** of pregnancy due to concerns about **folate antagonism** (trimethoprim) and potential teratogenic effects, such as neural tube defects, particularly between 6-12 weeks' gestation.
- The patient is at 12 weeks' gestation, making TMP/SMX a less safe choice compared to other antibiotics.
*Perform renal ultrasound*
- A **renal ultrasound** is typically performed if there are complications such as **pyelonephritis**, recurrent urinary tract infections, or suspicion of **structural abnormalities** in the urinary tract.
- For asymptomatic bacteriuria, an ultrasound is not part of the initial management unless there are specific indications or if the infection does not resolve with appropriate antibiotic therapy.
Urinary tract infections in children US Medical PG Question 9: A 13-month-old female infant is brought to the pediatrician by her stepfather for irritability. He states that his daughter was crying through the night last night, but she didn’t want to eat and was inconsolable. This morning, she felt warm. The father also notes that she had dark, strong smelling urine on the last diaper change. The patient’s temperature is 101°F (38.3°C), blood pressure is 100/72 mmHg, pulse is 128/min, and respirations are 31/min with an oxygen saturation of 98% on room air. A urinalysis is obtained by catheterization, with results shown below:
Urine:
Protein: Negative
Glucose: Negative
White blood cell (WBC) count: 25/hpf
Bacteria: Many
Leukocyte esterase: Positive
Nitrites: Positive
In addition to antibiotics, which of the following should be part of the management of this patient’s condition?
- A. Voiding cystourethrogram
- B. Renal ultrasound (Correct Answer)
- C. Prophylactic antibiotics
- D. Repeat urine culture in 3 weeks
- E. Hospitalization
Urinary tract infections in children Explanation: ***Renal ultrasound***
- A **renal ultrasound** is recommended for all infants and young children (age 2 months to 2 years) after their first febrile **urinary tract infection (UTI)**.
- This imaging is crucial to evaluate for any underlying **structural kidney abnormalities** or **urinary tract obstructions** that could predispose to recurrent UTIs.
*Voiding cystourethrogram*
- A **voiding cystourethrogram (VCUG)** is typically reserved for patients after an abnormal renal ultrasound or for those with **recurrent UTIs** to assess for **vesicoureteral reflux (VUR)**.
- Doing a VCUG after the first febrile UTI in every child is not typically recommended as initial management in the absence of other risk factors or ultrasound findings.
*Prophylactic antibiotics*
- **Prophylactic antibiotics** are generally indicated for children with recurrent UTIs or confirmed **vesicoureteral reflux (VUR)** to prevent future infections and renal damage.
- They are not routinely recommended after a first febrile UTI without further evaluation, such as identifying an underlying anatomical anomaly.
*Repeat urine culture in 3 weeks*
- A **repeat urine culture** is usually performed only if the initial UTI symptoms do not resolve with treatment or if there are concerns about treatment failure or **resistant organisms**.
- It's not a standard component of follow-up for an uncomplicated first febrile UTI in a child who responds well to antibiotics.
*Hospitalization*
- **Hospitalization** for intravenous antibiotics is considered for infants with a UTI who appear **toxic**, are unable to tolerate oral intake, or are very young (under 2-3 months of age).
- While this infant has a fever, she does not exhibit signs of severe illness or toxicity that would immediately warrant hospitalization solely based on the provided information.
Urinary tract infections in children US Medical PG Question 10: A 48-year-old man comes to the emergency department because of a 2-hour history of severe left-sided colicky flank pain that radiates towards his groin. He has vomited twice. Last year, he was treated with ibuprofen for swelling and pain of his left toe. He drinks 4-5 beers most days of the week. Examination shows left costovertebral angle tenderness. An upright x-ray of the abdomen shows no abnormalities. A CT scan of the abdomen and pelvis shows an 9-mm stone in the proximal ureter on the left. Which of the following is most likely to be seen on urinalysis?
- A. Rhomboid-shaped crystals
- B. Coffin-lid-like crystals
- C. Red blood cell casts
- D. Wedge-shaped crystals (Correct Answer)
- E. Hexagon-shaped crystals
Urinary tract infections in children Explanation: ***Wedge-shaped crystals***
- The patient's history of **left toe swelling and pain** (suggestive of **gout**) and **alcohol consumption** strongly indicate **hyperuricemia** and predisposition to **uric acid stone** formation.
- **Uric acid stones are radiolucent**, which explains why the **X-ray showed no abnormalities** despite a 9-mm stone being visible on CT scan—this is a classic presentation.
- **Uric acid crystals** appear as **wedge-shaped, rhomboid, or pleomorphic** yellow-brown crystals in **acidic urine** (pH <5.5).
- This is the most likely finding on urinalysis given the clinical context.
*Rhomboid-shaped crystals*
- **Rhomboid-shaped crystals** are also characteristic of **uric acid**, making this another acceptable description of the same crystal type.
- Both "wedge-shaped" and "rhomboid" refer to **uric acid crystals**; however, "wedge-shaped" is the more commonly used descriptor in clinical practice.
- If this were an option and wedge-shaped were not available, it would also be correct, but wedge-shaped is the better answer when both are present.
*Coffin-lid-like crystals*
- **Coffin-lid crystals** are characteristic of **struvite stones** (magnesium ammonium phosphate), which form in **alkaline urine** (pH >7) and are associated with **urease-producing bacteria** (e.g., Proteus, Klebsiella).
- Struvite stones are **radiopaque** and would be visible on X-ray, which contradicts this presentation.
- The patient has no signs of urinary tract infection.
*Red blood cell casts*
- **RBC casts** indicate **glomerular bleeding** and are seen in conditions like **glomerulonephritis**, not obstructive uropathy from stones.
- While **hematuria** (RBCs in urine) is common with nephrolithiasis, **RBC casts** are not typical and would suggest primary renal parenchymal disease.
*Hexagon-shaped crystals*
- **Hexagonal crystals** are pathognomonic for **cystine stones**, which occur in **cystinuria**, a rare autosomal recessive disorder of amino acid transport.
- Cystine stones are **weakly radiopaque** and would show faint opacity on X-ray.
- This condition typically presents in childhood or young adulthood, not at age 48, and has no association with gout.
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