Nephrology

Question 1

When should inguinal hernias be repaired?

Answer 1

Answer
On diagnosis
Explanation
All inguinal hernias should be repaired as soon as possible after diagnosis. Strangulated hernias are a surgical emergency!

Question 2

What is the calculation for urine anion gap (UAG)?

Answer 2

Answer
UAG = Na+ + K+ − Cl–
Explanation
Normal anion gap metabolic acidosis (NAGMA; a.k.a. hyperchloremic acidosis) is caused by a loss of HCO3–, with a commensurate increase in Cl– (the Cl– is increased to maintain electrical neutrality). NAGMA typically occurs via the kidney (renal tubular acidosis [RTA]) or the GI tract (diarrhea). UAG is used to differentiate between these 2 as the cause of NAGMA:

UAG is positive with NAGMA due to RTA.
UAG is negative with NAGMA due to GI losses.
Remember: neGUTive—negative UAG in bowel cases.

Question 3

What is the most common cause of nephrotic syndrome in children?

Answer 3

Answer
Minimal change nephrotic syndrome (MCNS; a.k.a. minimal change disease)
Explanation
MCNS is the most common type of nephrotic syndrome in childhood (60−85% of cases in patients < 10 years of age and 65% of pediatric cases overall). It is almost always idiopathic but has been associated with Hodgkin lymphoma, NSAIDs, and systemic immune-mediated diseases. A history of atopy occurs in 30–60% of affected children.

Question 4

What microorganism is commonly associated with staghorn renal calculi?

Answer 4

nswer
Proteus
Explanation
 Struvite kidney stones are composed of magnesium ammonium phosphate and calcium carbonate apatite crystals. They grow quickly and often cause staghorn calculi. Think infection when you see these. Proteus is the most common organism associated with development of kidney stones, particularly staghorn calculi. Other organisms that can do this include Pseudomonas, yeast, and Staphylococcus. (Remember the charming mnemonic PPYS, pronounced “piss

Question 5

What is the most common cause of obstructive uropathy that leads to renal failure in childhood?

Answer 5

Posterior urethral valves (PUVs)
Explanation
PUVs are a pair of obstructing leaflets in the prostatic urethra of newborn males. Most cases are discovered in utero with bilateral hydroureteronephrosis. Do a voiding cystourethrogram after birth to make the diagnosis. These infants require immediate bladder drainage. Despite treatment (removal of the valves), damage is already done, and up to 30% of these boys will develop end-stage kidney disease during childhood.

Question 6

When should you begin yearly screening for albuminuria in patients with diabetes mellitus (DM) Type 1? Type 2?

Answer 6

Answer
In Type 1, begin 3–5 years after initial diagnosis; in Type 2, screen yearly after initial diagnosis.
Explanation
For patients with DM Type 1, you can wait several years before beginning annual albuminuria screens because you generally know the time of disease onset. For those with DM Type 2, start screening yearly after the initial diagnosis because you do not know how long they have had the disease.

Question 7

What is the best way to manage edema in a child with minimal change nephrotic syndrome (MCNS)?

Answer 7

Salt/sodium restriction
Explanation
With MCNS, it is vital to provide supportive and symptomatic care. Manage edema with salt restriction. Fluids can be restricted, but generally this is not necessary except in severe cases; defer the use of diuretics except in severe cases.

Question 8

What is the serious CNS complication you worry about with autosomal dominant polycystic kidney disease (ADPKD)

Answer 8

Berry aneurysms in the circle of Willis
Explanation
If these aneurysms rupture, they can be fatal. Like ADPKD itself, these aneurisms tend to run in specific families.

Question 9

Which type of renal tubular acidosis (RTA) most commonly causes renal stones?

Answer 9

Type 1 RTA (distal)
Explanation
The renal stones associated with Type 1 RTA are probably caused by decreased citrate excretion and hypercalciuria. Amphotericin B is one of the most common causes of Type 1 RTA.

Question 10

What is the most common cause of priapism?

Answer 10

Sickle cell disease (SCD)
Explanation
Priapism is a painful, unremitting erection in which the corpora cavernosa is rigid, but the glans and corporus spongiosum are flaccid. It is sometimes the presenting symptom of SCD!

Question 11

What is entrapment of a phimotic foreskin behind the glans of the penis called?

Answer 11

Paraphimosis
Explanation
Paraphimosis results in edema and swelling of the glans and foreskin. This is a medical emergency that can cause necrosis! Reduction (returning the foreskin to its normal position covering the glans) often requires sedation and local anesthesia.

Question 12

A 5-year-old boy with a history of URI 1 week ago presents with:

Purpuric rash on the buttocks, abdomen, and lower extremities
Abdominal pain
Arthralgias
Glomerulonephritis with IgA deposition
What is the most likely diagnosis?

Answer 12

Answer
IgA vasculitis (IgAV)
Explanation
IgAV (formerly Henoch-Schönlein purpura) peaks between 4 and 5 years of age. The renal lesion on histological exam looks just like IgA nephropathy. 90% have full recovery of renal function; however, 3–5% develop end-stage kidney disease, which can occur anywhere from a few months to several years after onset. Another 5% have evidence of chronic renal damage.

Question 13

You find a hydrocele on a 2-month-old.

When should the child undergo repair if it persists?

Answer 13

1 year of age
Explanation
Hydroceles that last past 1 year of age should be surgically repaired. Noncommunicating hydroceles usually resolve before this time.

Question 14

What condition is most associated with a very low FENa?

Answer 14

Prerenal acute kidney injury (AKI, a.k.a. prerenal azotemia)
Explanation
Prerenal AKI is due to decreased blood flow into the kidneys, with a resulting reduced glomerular filtration rate. Several factors can cause prerenal AKI, including certain drugs (e.g., diuretics [most common], NSAIDs, ACE inhibitors), renal artery stenosis, and cirrhosis. FENa is very low (< 1%) in prerenal AKI, making it a good 1st test to assess whether the AKI is prerenal or intrinsic. (FENa in intrinsic AKI is > 1%.) Interestingly, you can see a low FENa in many types of glomerulonephritis as well (since the glomerular injury is pretubular).

Question 15

Which type of renal tubular acidosis (RTA) is associated with Fanconi syndrome?

Answer 15

Type 2 RTA (proximal)
Explanation
Type 2 RTA is also associated with amino acid problems, heavy metal exposure, and cystinosis.

Question 16

A 17-year-old high school football player presents in August with:

Severe weakness
Nausea/Vomiting
Serum CK is markedly elevated.
High serum potassium
Creatinine is 3.1 mg/dL with a mildly elevated BUN.
U/A is heme positive but without RBCs.
Urine myoglobin is present.
Muddy-brown casts in the urine
What is the diagnosis?

Answer 16

Rhabdomyolysis
Explanation
Rhabdomyolysis is due to muscle trauma, strenuous exercise, seizures, heat stroke, severe volume contraction, cocaine use, hypophosphatemia, and/or severe hypokalemia. It can lead to acute tubular necrosis.

Question 17

What are the most common sites for thromboses in a child with nephrotic syndrome?

Answer 17

Renal vein and sagittal sinus
Explanation
In children with nephrotic syndrome, these are the most common locations for clots, followed by the pulmonary and femoral arteries. Almost all nephrotic children have a hypercoagulable state, and about 20% will have a thrombotic event that is clinically silent!

Question 18

Which type of serum anion gap is associated with all types of renal tubular acidosis (RTA)?

Answer 18

Normal anion gap
Explanation
RTA is a metabolic acidosis typically caused by a defect—often genetic—in renal tubule function due to the inability of the kidney to maintain high enough bicarbonate. All 3 types of RTA have a normal serum anion gap—i.e., all are hyperchloremic.

Question 19

What is the most common genital problem in newborn males?

Answer 19

Cryptorchidism
Explanation
Cryptorchidism (undescended testes) occurs in up to 33% of premature boys and in 3–4% of term males. By 1 year of age, the testes have descended in all but 0.3%.

Question 20

What is the most likely etiology in children with recurrent gross glomerular hematuria?

Answer 20

IgA nephropathy (a.k.a. Berger disease)
Explanation
IgA nephropathy is the most likely glomerular etiology in children presenting with recurrent gross hematuria.

Question 21

Autosomal dominant
Multiple family members have hematuria with or without RBC casts but no history of kidney failure.
Name the syndrome.

Answer 21

Thin basement membrane nephropathy (a.k.a. benign familial hematuria)
Explanation
Thin basement membrane nephropathy is an AD disease with hematuria but no long-term sequelae of renal disease. Biopsy of the kidney, though rarely performed, reveals a very thin basement membrane. No treatment is required and prognosis is good. However, long-term surveillance is required because some patients diagnosed with this condition go on to develop proteinuria and ­progressive chronic kidney disease over time.

Question 22

You start an aminoglycoside in a child. On day 8, his creatinine rises and his FENa is not low.

What is the mechanism by which the aminoglycoside likely caused acute kidney injury (AKI)?

Answer 22

Answer
Acute tubular necrosis (ATN)
Explanation
ATN is the most common cause of intrarenal AKI (about 75%!) in adults and is common in children. Aminoglycosides are one of several types of drugs that can induce ATN. They cause proximal tubule damage resulting in nonoliguric ATN. ATN is usually delayed 7–10 days after starting therapy, and early therapeutic levels are not a guarantee of safety!

Question 23

A 5-year-old Black girl with obesity presents with vaginal spotting in her underwear. Physical exam shows an everted, hemorrhagic, donut-shaped periurethral mass.

What is the most likely diagnosis?

Answer 23

Urethral prolapse
Explanation
Urethral prolapse occurs when the urethral mucosa completely extrudes through the external meatus. It is most commonly seen in Black girls between 4 and 10 years of age. Predisposing symptoms include coughing, constipation, trauma, urinary or vaginal infections, and obesity. Manage conservatively with topical estrogen cream, applied twice daily following a sitz bath. This often leads to resolution within 2–4 weeks. Surgery is required only if there is associated evidence of necrosis.

Question 24

What is an abnormal dilatation and tortuosity of the testicular vein and pampiniform plexus of the spermatic cord called?

Answer 24

Varicocele
Explanation
Varicoceles are found in 15–20% of adolescent boys and are unusual prior to puberty. They are almost exclusively on the left side. Repair these if the boy has atrophy or slow growth of the left testis compared to the right.

Question 25

A 20-year-old male presents with antiglomerular basement membrane (anti-GBM) disease.

On renal biopsy, what will be seen deposited in the glomerular basement membrane?

Answer 25

IgG and C3
Explanation
Finding crescentic nephritis and linear deposits of IgG and C3 in the GBM on renal biopsy confirms a diagnosis of anti-GBM disease. You can also find anti-GBM antibody in the plasma of 90% of patients.

Question 26

A newborn presents with:

History of oligohydramnios while in utero
Low-set ears
Flat nose
Retracted chin
Palpable enlarged kidneys
Hypertension
Hepatic fibrosis
What is the most likely diagnosis?

Answer 26

Autosomal recessive polycystic kidney disease (ARPKD)
Explanation
ARPKD disease results in bilateral kidney enlargement and transforms collecting ducts into fusiform cysts. Hepatic fibrosis is universal. Oligohydramnios occurs because of intrauterine renal failure. Potter facies (low-set ears, flat nose, and retracted chin) is due to decreased amniotic fluid with insufficient lung development. A finding of palpable kidneys is the most common feature of ARPKD, as well as hypertension and recurrent UTIs.

Question 27

A boy is born with hypospadias.

Should he have a circumcision?

Answer 27

No
Explanation
Neonatal circumcision should not be performed on a boy with hypospadias because hypospadias repair uses preputial skin. Hypospadias is typically an isolated event and does not require genitourinary workup.

Question 28

An 8-year-old boy presents with:

History of documented streptococcal pharyngitis 10 days ago, treated with IM penicillin
He presents today with edema and cola-colored urine.
What do you expect his complement levels (C3 and C4) to be?

Answer 28

C3: Low
C4: Likely normal, rarely mildly low
Explanation
The boy has acute poststreptococcal glomerulonephritis (APSGN), and the key laboratory finding is a low C3 level, which will remain low for 2–12 weeks (the C3 levels eventually normalize). Contrast this with IgA nephropathy, where the hematuria occurs concurrently with the infection (no latency) and the C3 level is normal. The latency period between pharyngitis and APSGN is 1–2 weeks; with skin infection, the latency is 3–6 weeks. Membranoproliferative glomerulonephritis, which can also present with gross hematuria and edema with or without a preceding infection, is associated with reduced C3 (and sometimes C4 as well) levels persisting beyond 12 weeks.

Question 29

How do you calculate the osmolal gap (OG)?

Answer 29

OG = measured osmolality − calculated osmolality
Calculated osmolality (OSMcalc) = 2[Na⁺] + (BUN/2.8) + (glucose/18)
Explanation
The osmolality of the blood is determined mainly by concentrations of sodium, glucose, and urea. The OG is the difference between the measured serum osmolality (from the lab) and a calculated estimation of what the osmolality ought to be—if the only effective osmoles present are the normal ones (Na+, glucose, and urea). A normal OG is < 10 mOsm/kg. An extremely high OG (> 25 mOsm/kg) is almost always due to toxic alcohol poisoning.

Question 30

Which specific antibody is commonly found in granulomatosis with polyangiitis (GPA)?

Answer 30

Anti-proteinase-3 (anti-PR3)
Explanation
In 80–90% of patients, GPA is confirmed by ­positive anti-PR3 antibodies that produce a c-ANCA pattern. The c-ANCA test is sensitive and ­specific for GPA.

Question 31

Which type of renal tubular acidosis (RTA) is associated with high serum potassium?

Answer 31

Type 4 RTA (hypoaldosteronism)
Explanation
Type 1 RTA has low K+ and Type 2 RTA can have low-to-normal K+. Only Type 4 RTA is associated with elevated serum K+.

Question 32

A patient presents with:

High anion gap metabolic acidosis (HAGMA)
High osmolal gap (OG)
Calcium oxalate crystals in the urine
What is the most likely ingestion?

Answer 32

Ethylene glycol (antifreeze)
Explanation
Ethylene glycol, propylene glycol, and methanol are the classic toxic alcohols that present with a HAGMA and a high OG. Here are some facts on each:
Ethylene glycol: Most of its effects are kidney related, and you will see calcium oxalate crystals in the urine.
Propylene glycol: Used as a solvent for intravenous lorazepam (and other drugs) and is an FDA-approved food sweetener. Continuous infusion or repeated large IV doses of lorazepam or sustained intestinal absorption of propylene glycol can cause severe lactic acidosis.
Methanol: Metabolizes to formic acid, a substance that is directly toxic to the optic nerve. Visual symptoms are the key clue.

Question 33

A 14-year-old girl presents for evaluation. She had a urine dipstick done at school by the school nurse and was told that it showed “protein.” She is not hypertensive and has no family history of renal disease. She is growing well and actually just hit her growth spurt in the last 6 months. Repeat urinalysis in your office shows proteinuria again. Otherwise, the urinalysis is normal.

What diagnosis should you consider first?

Answer 33

Answer
Benign orthostatic proteinuria
Explanation
This can occur in up to 10–20% of adolescents (particularly girls), especially during the growth spurt. Check supine and upright urine proteins for diagnosis. (The proteinuria reverts to normal values when the patient is supine.) A first morning urine specimen is helpful in diagnosis. Benign orthostatic proteinuria is, as it says, a benign condition not associated with pathology.

Question 34

What type of casts are seen in acute tubular necrosis (ATN)?

Answer 34

Large, muddy-brown granular casts (if any)
Explanation
Hallmark urine findings in ATN include red or brown urine with large, muddy-brown granular casts (not always present). Oliguric ATN commonly resolves in 1–4 weeks

Question 35

What should you consider if you find eosinophils on a urinalysis?

Answer 35

Allergic interstitial nephritis
Explanation
Eosinophilia on a urinalysis should make you think of drug-induced hypersensitivity-mediated interstitial nephritis.

Question 36

Does antibiotic therapy prevent acute poststreptococcal glomerulonephritis (APSGN)?

Answer 36

No
Explanation
APSGN follows after infections with specific ­nephritogenic strains of Streptococcus pyogenes (group A β-hemolytic strep). The risk of this occurring is believed to be ∼ 10–15%. Treatment with antibiotics does not prevent APSGN, but it does prevent rheumatic fever, another potential late Streptococcus infection complication.

Question 37

An 8-year-old boy presents with:

An upper respiratory infection
Cola-colored urine
Transient rise in creatinine
What is the most likely diagnosis?

Answer 37

IgA nephropathy (a.k.a. Berger disease)
Explanation
The key here is that the URI is occurring at the same time as the hematuria (sometimes the hematuria can happen a few hours or days after the URI); thus, this can be due to IgA nephropathy. A transient rise in creatinine can also occur in IgA nephropathy. Remember: Acute postinfectious glomerulonephritis occurs 1–2 weeks after pharyngitis.

Question 38

What is the most common congenital anomaly of the penis?

Answer 38

Answer
Hypospadias
Explanation
Hypospadias occurs in 1/300 males and results in the abnormal positioning of the urethral meatus proximal to the tip of the glans. Hypospadias occurs most commonly as an isolated event, and no imaging of the upper GU system is required.

Question 39

What risk is associated with undescended testes?

Answer 39

Malignancy
Explanation
Persistently undescended testes have an increased risk of cancer, especially seminoma—this is why we must fix them. Boys whose testes are still undescended by 6 months of age should be referred for surgical evaluation. Orchiopexy is likely to be performed between 6 and 18 months of age to decrease the risk of infertility and malignancy.

Question 40

A newborn male presents with retractile testes that can be pulled down into the scrotum, but on letting go, they end back up superiorly.

What should be done at this point?

Answer 40

Answer
Watchful waiting
Explanation
Almost all retractile testes eventually end up in the scrotum, so no further management is necessary.

Question 41

What is the organism most commonly associated with hemolytic uremic syndrome (HUS)?

Answer 41

Escherichia coli O157:H7
Explanation
Nearly 90% of children with HUS have a preceding diarrheal illness due to E. coli O157:H7, which produces a Shiga-like toxin.

Question 42

What is the most common cause of hydronephrosis in infancy and childhood?

Answer 42

Ureteropelvic junction obstruction (UPJ)
Explanation
UPJ is frequently found on prenatal ultrasound and is suspected when only the renal pelvis is dilated but the ureter is not.

Question 43

Autosomal dominant
Hypoplasia or absence of the patellae
Dystrophic nails
Dysplasia of the elbows
Renal disease with microhematuria and mild proteinuria—10% of cases progress to end-stage kidney disease (ESKD).
What syndrome has these findings?

Answer 43

Nail-patella syndrome
Explanation
There is no specific therapy for the nephropathy of nail-patella syndrome, but renal transplant appears to be effective in patients who progress to ESKD. This is a rare disorder in practice, but it is commonly seen on exams!

Question 44

A boy presents with a history of hematuria at the end of urinating, evidenced by spotting of blood in the underwear. Physical examination and ultrasound are normal.

What is the most likely diagnosis?

Answer 44

Urethrorrhagia
Explanation
Urethrorrhagia occurs only in boys. The process is self-limited and requires no specific therapy but can take up to a year or longer to resolve. The symptoms are usually intermittent and recurrent.

Question 45

A young boy presents with the following:

Absence of abdominal wall musculature
Cryptorchidism
Dilation of the prostatic urethra, bladder, and ureters
What is the syndrome with these findings?

Answer 45

Prune belly syndrome (a.k.a. Eagle-Barrett syndrome, urethral obstruction malformation complex)
Explanation
Prune belly syndrome occurs in about 1/40,000 boys and is much rarer in girls, who make up only 5% (or 1/800,000) of all cases. The syndrome gets its name from the shriveled, prune-like skin on the infant’s abdominal wall. It can have varied presentations, but the most common is a group with significant anatomical genitourinary anomalies but often initially normal renal function. It can be confused with posterior urethral valves in utero. Due to poor bladder emptying, children with prune belly syndrome have chronic kidney disease and some will develop end-stage kidney disease.

Question 46

A patient presents with:

Polyuria
Polydipsia
Anemia
Failure to thrive
Salt-wasting nephropathy—with no signs of nephritis or nephrotic syndrome
The patient also has these extrarenal manifestations:
Inability to perform horizontal eye movements
Retinitis pigmentosa
Cerebellar aplasia with coloboma of the eye
What is the most likely diagnosis?

Answer 46

Juvenile nephronophthisis Type 1 (NPH1)
Explanation
Although the most common form of nephronophthisis, juvenile NPH1 is a rare AR disease. The strange thing to remember is that this is a salt-wasting nephropathy without nephrotic or nephritic syndrome. Renal ultrasound shows poor differentiation between the cortical and medullary areas of the kidney. After 9 years of life, cysts are common at the corticomedullary border. End-stage kidney disease occurs, on average, by 13 years of age.

Question 47

What is a commonly used potassium-sparing diuretic?

Answer 47

Spironolactone
Explanation
Spironolactone is an aldosterone antagonist, so it is K+ sparing and, hence, can also cause acidosis. Eplerenone, triamterene, and amiloride are also K+ sparing.

Question 48

What is it called when the penile foreskin cannot be retracted?

Answer 48

Answer
Phimosis
Explanation
Physiologic phimosis is the most common cause, followed by iatrogenic injury from forcible retraction. Most foreskins are easily retracted by 4 years of age

Question 49

A 12-year-old presents with bedwetting. She had been dry for years and suddenly has trouble staying dry all night.

What should you consider as one of your first diagnoses to investigate?

Answer 49

Child abuse
Explanation
Always consider sexual, physical, or emotional abuse in all voiding disorders. A good bedwetting evaluation in this case could save the child’s life!

Question 50

What additional vaccine(s) should a child with minimal change nephrotic syndrome receive?

Answer 50

PPSV23 (23-valent pneumococcal vaccine)
Explanation
For children with all types of nephrotic syndrome, both pneumococcal vaccines are recommended. Make sure the child has received the recommended PCV13 inoculations, and add PPSV23 in accordance with the CDC immunization schedule.

Question 51

How do you calculate the serum anion gap (AG)?

Answer 51

AG = Na+ − (HCO3– + Cl–)
Explanation
Remember, physiologically there is no true “gap”; the term just refers to the usual amount of unmeasured anions in serum (or urine).

Question 52

A boy presents with:

Persistent microhematuria
Proteinuria
Hypertension
Sensorineural deafness
Perimacular pigment changes
He has a maternal uncle with the same disease process.

What is the most likely diagnosis?

Answer 52

Answer
Alport syndrome
Explanation
Alport syndrome arises from mutations in the genes that encode for Type 4 collagen, which makes up the collagen part of basement membranes of the kidneys, ears, and eyes. About 80% of cases are X-linked. Consider this diagnosis in any child with hematuria (microscopic and/or recurrent gross), ocular problems, hearing loss, and a family history of early hearing loss and kidney disease.

Question 53

What is the most common cause of bilateral urinary obstruction in male infants?

Answer 53

Answer
Posterior urethral valves (PUVs)
Explanation
PUVs are a pair of obstructing leaflets in the prostatic urethra. PUVs are the most common cause of obstructive uropathy that leads to kidney failure in childhood. They occur in about 1/5,000 males. Most cases are discovered in utero with bilateral hydroureteronephrosis.

Question 54

What is the most common disease of autosomal dominant inheritance in the U.S.?

Answer 54

Answer
Autosomal dominant polycystic kidney disease (ADPKD)
Explanation
The prevalence of ADPKD in the U.S. is 1–2 per 1,000 births. End-stage kidney disease generally doesn’t develop until 50–60 years of age. For children who have parents with the disease, a single cyst on a kidney in childhood is highly predictive of development of ADPKD as an adult.