Chem Path 7 - Paediatric Clinical Chemistry

Question 1

List some common problems in LBW babies.

Answer 1

Respiratory distress syndrome

Retinopathy of prematurity

Intraventricular haemorrhage

Patent ductus arteriosus

Necrotising enterocolitis

Question 2

What is necrotising enterocolitis?

Answer 2

Inflammation of the bowel wall progressing to necrosis and perforation

Characterised by bloody stools, abdominal distension and intramural air (pneumatosis intestinalis)

Question 3

List some key differences of the neonatal kidneys compared to adult kidneys and their implications.

Answer 3

Short proximal tubule so lower reabsorptive capability

Reduce reabsorption of bicarbonate leading to a propensity to acidosis

Loop of Henle and distal collecting ducts are short and juxtaglomerular leading to reduced concentrating ability (maximum urine osmolality of 700 mmol/kg)

Distal tubule is relatively unresponsive to aldosterone leading to persistent sodium loss and reduced potassium excretion (sodium loss of 1.8 mmol/kg/day, and upper limit of normal K+ of 6 mmol/L in neonates)

Question 4

Why does glycosuria occur at a lower plasma glucose level in neonates?

Answer 4

Short proximal tubule means that they have a lower ability to reabsorb glucose

Question 5

Describe how body water content is different in neonates compared to adults.

Answer 5

Term neonates are 75% water compared to 60% in adults (and 85% in preterm infants)

Question 6

What happens to the body water content in the first week of life?

Answer 6

Pulmonary resistance drops and you get release of ANP leading to redistribution of fluid

This can lead to up to 10% weight loss within the first week of life

Roughly 40 mL/kg loss in preterm infants

Question 7

How are the daily fluid and electrolyte requirements different in neonates compared to adults?

Answer 7

Sodium, potassium and water requirements are higher

NOTE: sodium requirements are particularly high in preterm neonates (< 30 weeks), so plasma Na+ should be measured daily in these patients. K+ supplements should be given once urine output > 1 mL/kg/hr has been achieved

Question 8

Why do babies have higher insensible water loss?

Answer 8

High surface area

Increased skin blood flow

High respiratory rate and metabolic rate

Increased transdermal fluid loss

NOTE: skin is not keratinised in premature infants

Question 9

Drugs can cause electrolyte disturbances in neonates. Give examples of drugs that can do this and briefly describe the mechanism.

Answer 9

Bicarbonate for acidosis (contains high Na+)

Antibiotics (usually sodium salts)

Caffeine/theophylline (for apnoea) – increases renal Na+ loss

Indomethacin (for PDA) – causes oliguria

NOTE: growth can also cause electrolyte disturbance

Question 10

What is hypernatraemia usually caused by in neonates?

Answer 10

Dehydration

NOTE: usually uncommon after 2 weeks

NOTE: food poisoning and osmoregulatory dysfunction are differentials

Question 11

What is hyponatraemia usually caused by in neonates?

Answer 11

Congenital adrenal hyperplasia

Question 12

Outline the pathophysiology of congenital adrenal hyperplasia.

Answer 12

Most commonly caused by 21-hydroxylase deficiency

Leads to reduce cortisol and aldosterone production and shunting of 17-OH progesterone and 17-OH pregnenelone which goes towards androgen synthesis

Question 13

Outline the clinical features of congenital adrenal hyperplasia.

Answer 13

Hyponatraemia/hyperkalaemia

Hypoglycaemia

Ambiguous genitalia in female neonates

Growth acceleration

Question 14

List three reasons for neonatal hyperbilirubinaemia.

Answer 14

High level of bilirubin synthesis

Low rate of transport into the liver

Enhanced enterohepatic circulation

Question 15

What is the issue with free bilirubin?

Answer 15

It can cross the blood-brain barrier leading to kernicterus

Question 16

What are the three bilirubin thresholds in neonates?

Answer 16

No treatment

Phototherapy

Exchange transfusion

Question 17

List some causes of neonatal jaundice.

Answer 17

G6PD Deficiency

Haemolytic anaemia (ABO, rhesus)

Crigler-Najjar syndrome

Question 18

What is prolonged jaundice?

Answer 18

Jaundice that lasts > 14 days in term babies or > 21 days in preterm babies

Question 19

List some causes of prolonged jaundice.

Answer 19

Prenatal infection/sepsis

Hypothyroidism

Breast milk jaundice

Question 20

What level of conjugated hyperbilirubinaemia is considered pathological?

Answer 20

More than 20 µmol/L

Question 21

List some causes of conjugated hyperbilirubinaemia.

Answer 21

Biliary atresia (MOST COMMON)

Choledochal cyst

Ascending cholangitis in TPN

Inherited metabolic diseases (e.g. galactosaemia, alpha-1 antitrypsin deficiency, tyrosinaemia, peroxisomal disorders)

NOTE: 20% of biliary atresia is associated with cardiac malformations, polysplenia, situs inversus

Question 22

How are calcium and phosphate levels different in babies?

Answer 22

After birth, calcium levels will fall

Phosphate is higher in babies (they are good at reabsorbing it)

Question 23

List the main biochemical features of osteopaenia of prematurity.

Answer 23

Calcium is usually normal

Phosphate < 1 mmol/L

ALP > 1200 U/L (10 x adult ULN)

Question 24

How is osteopaenia of prematurity treated?

Answer 24

Phosphate/calcium supplements

1-alpha calcidol

Question 25

List some presenting features of rickets.

Answer 25

Frontal bossing

Bowed legs

Muscular hypotonia

Tetany/hypocalcaemic seizure

Hypocalcaemic cardiomyopathy

Question 26

List some genetic causes of rickets.

Answer 26

Pseudo-vitamin D deficiency I (defective renal hydroxylation)

Pseudo-vitamin D deficiency II (receptor defect)

Familial hypophosphataemias (low tubular maximum reabsorption of phosphate, raised urine phosphoethanolamine)

NOTE: top two conditions are treated with 1,25-OH Vitamin D