A 5-month-old boy is brought to the pediatrician by his parents, who began noticing that the infant was not able to hold his head upright when sitting or in a prone position. Upon examination, the infant has a musty odor, fair skin with patches of eczema, and blue eyes. The pediatrician orders laboratory tests and prescribes a special diet. Which of the following amino acids becomes essential and must be supplemented in this patient's condition?

Phenylalanine-free amino acid formula

A 6-month-old male presents to the emergency department with his parents after his three-year-old brother hit him on the arm with a toy truck. His parents are concerned that the minor trauma caused an unusual amount of bruising. The patient has otherwise been developing well and meeting all his milestones. His parents report that he sleeps throughout the night and has just started to experiment with solid food. The patient’s older brother is in good health, but the patient’s mother reports that some members of her family have an unknown blood disorder. On physical exam, the patient is agitated and difficult to soothe. He has 2-3 inches of ecchymoses and swelling on the lateral aspect of the left forearm. The patient has a neurological exam within normal limits and pale skin with blue irises. An ophthalmologic evaluation is deferred. Which of the following is the best initial step?

Complete blood count and coagulation panel

Ensure the child's safety and alert the police

A 35-year-old woman gravida 2, para 1, comes to the physician for her first prenatal visit. Pregnancy and delivery of her first child were uncomplicated. She is not sure about the date of her last menstrual period. Pelvic examination shows a uterus consistent in size with a 10-week gestation. An ultrasound examination confirms the gestational age and shows one fetus with no indication of multiple gestations. During counseling on pregnancy risks and possible screening and diagnostic tests, the patient states she would like to undergo screening for Down syndrome. She would prefer immediate and secure screening with a low risk to herself and the fetus. Which of the following is the most appropriate next step in management at this time?

Nuchal translucency, pregnancy-associated plasma protein-A, human chorionic gonadotropin

Maternal serum α-fetoprotein, human chorionic gonadotropin, unconjugated estriol, and inhibin A

During the selection of subjects for a study on infantile vitamin deficiencies, a child is examined by the lead investigator. She is at the 75th percentile for head circumference and the 80th percentile for length and weight. She can lift her chest and shoulders up when in a prone position, but cannot roll over from a prone position. Her eyes follow objects past the midline. She coos and makes gurgling sounds. When the investigator strokes the sole of her foot, her big toe curls upward and there is fanning of her other toes. She makes a stepping motion when she is held upright and her feet are in contact with the examination table. Which of the following additional skills or behaviors would be expected in a healthy patient of this developmental age?

Cries when separated from her mother

Responds to calling of own name

A 27-year-old G1P0 female presents for her first prenatal visit. She is in a monogamous relationship with her husband, and has had two lifetime sexual partners. She has never had a blood transfusion and has never used injection drugs. Screening for which of the following infections is most appropriate to recommend this patient?

Syphilis, HIV, HBV, and chlamydia

No routine screening is recommended for this patient

A 36-year-old primigravida presents to her obstetrician for antenatal care. She is at 24 weeks of gestation and does not have any current complaint except for occasional leg cramps. She does not smoke or drink alcohol. Family history is irrelevant. Her temperature is 36.9°C (98.42°F), blood pressure is 100/60 mm Hg, and pulse of 95/minute. Her body mass index is 21 kg/m² (46 pounds/m²). Physical examination reveals a palpable uterus above the umbilicus with no other abnormalities. Which of the following screening tests is suitable for this patient?

Oral glucose tolerance test for gestational diabetes mellitus

Fasting and random glucose testing for gestational diabetes mellitus

HbA1C for gestational diabetes mellitus

Complete blood count for iron deficiency anemia

Wet mount microscopy of vaginal secretions for bacterial vaginosis

A 3-year-old boy is brought to his pediatrician by his parents for a follow-up visit. Several concerning traits were observed at his last physical, 6 months ago. He had developmental delay, a delay in meeting gross and fine motor control benchmarks, and repetitive behaviors. At birth, he was noted to have flat feet, poor muscle tone, an elongated face with large, prominent ears, and enlarged testicles. He takes a chewable multivitamin every morning. There is one other member of the family, on the mother’s side, with a similar condition. Today, his blood pressure is 110/65 mm Hg, heart rate is 90/min, respiratory rate is 22/min, and temperature of 37.0°C (98.6°F). On physical exam, the boy repetitively rocks back and forth and has difficulty following commands. His heart has a mid-systolic click, followed by a late systolic murmur and his lungs are clear to auscultation bilaterally. Several vials of whole blood are collected for analysis. Which of the following studies should be conducted as part of the diagnostic screening protocol?

Two-dimensional gel electrophoresis

PCR followed by northern blot with RNA probes

A worried mother brings her 12-day-old son to the emergency room concerned that his body is turning "yellow". The patient was born at 39 weeks via spontaneous vaginal delivery without complications. The mother received adequate prenatal care and has been breastfeeding her son. The patient has had adequate urine and stool output. Physical exam demonstrates a comfortable, well nourished neonate with a jaundiced face and chest. The patient's indirect bilirubin was 4 mg/dL at 48 hours of life. Today, indirect bilirubin is 10 mg/dL, and total bilirubin is 11 mg/dL. All other laboratory values are within normal limits. What is the next best treatment in this scenario?

Stop breastfeeding and switch to formula

Reassure mother that jaundice will remit, advise her to continue breastfeeding

A 10-year-old girl is admitted to the medical floor for a respiratory infection. The patient lives in a foster home and has been admitted many times. Since birth, the patient has had repeated episodes of pain/pressure over her frontal sinuses and a chronic cough that produces mucus. She was recently treated with amoxicillin for an infection. The patient is in the 25th percentile for height and weight which has been constant since birth. Her guardians state that the patient has normal bowel movements and has been gaining weight appropriately. The patient has a history of tricuspid stenosis. She also recently had magnetic resonance imaging (MRI) of her chest which demonstrated dilation of her airways. Her temperature is 99.5°F (37.5°C), blood pressure is 90/58 mmHg, pulse is 120/min, respirations are 18/min, and oxygen saturation is 94% on room air. Physical exam is notable for bruises along the patient's shins which the guardians state are from playing soccer. The rest of the exam is deferred because the patient starts crying. Which of the following findings is associated with this patient's most likely underlying diagnosis?

Increased chloride in the patient's sweat

Social withdrawal and avoidance of eye contact

Repeat sinus infections secondary to seasonal allergies

Diastolic murmur best heard along the right lower sternal border

Newborn screening programs for USMLE Step 2 CK: High-Yield Pediatrics Lessons

NBS Principles - Spotting Trouble Early

Newborn Screening (NBS) is a public health program for early detection of serious, treatable conditions before symptoms appear.

Core tenets are based on the Wilson-Jungner criteria:

The Condition: An important health problem with a recognizable latent or early symptomatic stage.
The Test: A suitable, reliable, and acceptable screening test must be available.
The System: An accepted treatment and facilities for diagnosis/treatment must be available. The cost should be economically balanced.

The US Recommended Uniform Screening Panel (RUSP) is a key global benchmark.

⭐ Ideal Sample Timing: Heel prick blood sample is best collected 24-72 hours after birth, ensuring adequate protein feeding.

Indian NBS - The National Picture

Rashtriya Bal Swasthya Karyakram (RBSK): India's ambitious public health initiative for early identification and intervention in children.
Core Strategy: The '4Ds' approach.
- Defects at birth
- Deficiencies
- Diseases
- Developmental delays including disability
Screened Conditions (National Mandate):
- Congenital Hypothyroidism (CH)
- Congenital Adrenal Hyperplasia (CAH)
- G6PD Deficiency
- Phenylketonuria (PKU)
- Galactosemia
- Sickle Cell Disease
Status: Not yet universal. Varies by state.
- Universal NBS: Kerala, Goa.
- Pilot Programs: Active in multiple other states.

⭐ RBSK targets comprehensive screening for over 27 crore children from birth to 18 years of age, a unique and wide-ranging age group for a national child health program.

The Usual Suspects - Disorders & Samples

Sample Collection: Heel prick blood spot collected on a Guthrie card.
Ideal Timing: 24-72 hours after birth. This timing is crucial to allow for clearance of maternal enzymes and for the infant to have sufficient protein intake, making metabolic disorders detectable.

Disorder	Defective Enzyme/Protein	Key Clinical Finding (Untreated)	Test
Congenital Hypothyroidism	Thyroid hormone synthesis	Intellectual disability, coarse facies	TSH, T4
Phenylketonuria (PKU)	Phenylalanine hydroxylase	Severe intellectual disability, seizures, musty odor	Tandem Mass Spectrometry (TMS)
Galactosemia	Galactose-1-phosphate uridyltransferase (GALT)	Cataracts, liver failure, E. coli sepsis	GALT activity, Beutler test
G6PD Deficiency	Glucose-6-Phosphate Dehydrogenase	Neonatal jaundice, acute hemolytic anemia	G6PD enzyme assay
Cystic Fibrosis	CFTR protein	Meconium ileus, recurrent lung infections	Immunoreactive trypsinogen (IRT)

Lab & Follow-Up - Test, Trace, Treat

Primary Technology: Tandem Mass Spectrometry (TMS) is the workhorse, measuring acylcarnitines and amino acids from a single dried blood spot.
Hormonal Assays: Immunoassays are used for non-amino acid disorders, like measuring TSH for congenital hypothyroidism or 17-OHP for CAH.

⭐ Optimal sample collection time: 48-72 hours after birth. A sample taken before 24 hours is often invalid, especially for detecting Phenylketonuria (PKU), due to insufficient protein intake.

High-Yield Points - ⚡ Biggest Takeaways

Newborn Screening (NBS) in India, under the RBSK program, is opportunistic, not yet universal.

Congenital Hypothyroidism (CH) is the most common disorder detected, making it a top priority.

Sample is collected via heel prick onto a filter paper card, ideally between 24-72 hours of life.

Tandem Mass Spectrometry (TMS) is the core technology, enabling screening for multiple disorders from one blood spot.

A positive screen is NOT diagnostic; it mandates a specific confirmatory test for diagnosis.

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