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a path 3 > CHEMPATH: Paediatric clinical chemistry > Flashcards

CHEMPATH: Paediatric clinical chemistry Flashcards

1
Q

What is the rate of infant death in the first year similar to?

A

Same as in adults aged 55-64 yo.

Highest in LBW infants

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2
Q

What are the common consitions seen in LBW infants?

A
  • Respiratory distress syndrome (RDS) - Common before 34th week of pregnancy, lack the surfactant protein in the lungs
  • Retinopathy of prematurity (ROP) - an abnormal growth of blood vessels in the eye –> vision loss
  • Intraventricular haemorrhage (IVH)
  • Patent ductus arteriosus (PDA)
  • Necrotising enterocolitis (NEC)
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3
Q

What are the features of NEC?

A

Inflammation of the bowel wall à necrosis and perforation

  • bloody stools,
  • abdominal distension
  • intramural air
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4
Q

What kind of preparation for birth does the foetus undergo in the last trimester of pregnancy?

A

Laying down stores e.g. fat and glycogen

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5
Q

When do nephrons form? When does urine production begin? When does complement form? When is functional maturity of GFR reached?

A

Nephrons - 6 weeks

Urine - 10 weeks

Full complement - 36 weeks

GFR functional maturity - 2 yo

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6
Q

What are the differences in infant kidney anatomy compared to adults?

A
  1. Glomerulus: large SA:volume ratio (so relatively low GFR for their SA)
  2. PCT: shorter
  3. Loop of Henle/DCT: shorter and DCT is relatively unresponsive to aldosterone
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7
Q

What are the consequences of large SA:volume ratio of the infant glomerulus?

A
  • Slow excretion of solute load
  • Limited amount of Na+ available for H+ exchange
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8
Q

What are the consequences of short PCT in infant kidneys?

A
  1. Lower resorptive capability BUT this is still adequate for the filtered load
  2. Renal threshold for glycosuria is much lower (i.e. glycosuria will appear at lower plasma glucose levels than in adults)
  3. Reabsorption of bicarbonate is not as effective –> propensity for acidosis
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9
Q

What are the consequences of short loop of Henle/DCT and reduced aldosterone sensitivity of the infant kidney?

A
  1. Short –> reduced concentration ability (max to osmolality of 700mmol/kg vs 1500mmol/kg in adults)
  2. Unresponsive to aldosterone –> persistent Na loss (1.8mmol/kg/day) –> THEREFORE reduced potassium* excretion

*So upper limit of normal is 6mmol/L in children up to 4yo

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10
Q

Why do ALL infants lose weight in the first 7 days of life? How much loss is normal in a term and preterm infant?

A
  • In utero they have more ECF than adults
  • Ex utero they have less pulmonary resistance –> release of ANP –> redistribution of fluid –> weight loss in the first 7 days of life

Loss of 40ml/kg in a term baby and 100ml/kg in a preterm baby

NB: should gain weight by days 7-10

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11
Q

What % of adult body vs preterm vs term infant is composed of water?

A

Adult = 60%

Term neonate= 75%

Preterm neonate = 85%

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12
Q

Daily requirements of water, K and Na for neonates vs adults of a proportional size.

A
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13
Q

How often should you monitor sodium levels in preterm infants? When can K+ be supplemented if necessary?

A
  1. Plasma Na+ should be measured daily in neonates born <30 weeks
  2. K+ should only be given once urine output of >1ml/kg/hr has been achieved [normal adult output]
  • In adults aldosterone –> increase K+ excretion AND increase Na+ reabsorption
  • Since infants have aldosterone insensitivity –> reduced K+ excretion (mild hyperkalaemia) and persistent Na+ losses so at risk of hypernatraemia and so must be monitored and fed often.
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14
Q

Name 3 broad causes of electrolyte disturbances in neonates.

A
  1. High insensible water loss
  2. Drugs
  3. Growth
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15
Q

Why do infants have high insensible water loss?

A
  • ​High surface area
  • High skin blood flow
  • High metabolic/respiratory rate
  • High transepidermal fluid loss (skin is not keratinised in premature infants, occurs >28 weeks)
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16
Q

Which drugs commonly given to infants cause electrolyte disturbances?

A
  • Bicarbonate (for acidosis) BUT Na bicarb contains high sodium
  • Antibiotics BUT contains high sodium content (sodium salts)
  • Caffeine/theophylline (for apnoea) BUT increases renal sodium loss
  • Indomethacin (for PDA) BUT causes oliguria
17
Q

Name 3 causes of hypernatraemia in an infant >2 weeks old. How should the cause be investigated?

A
  1. Dehydration
  2. Salt poisoning*
  3. Osmoregulatory dysfunction

Ix: Routine measurement of urea, creatinine and electrolytes on paired urine and plasma on admission may differentiate the rare causes but keep salt poisoning at back of your mind.

18
Q

Name a congenital disorder which can cause hyponatraemia in an infant.

A

CAH (congenital adrenal hyperplasia)

19
Q

How does CAH cause hyponatraemia? How does CAH cause ambiguous genitalia in female infants?

A

Most common cause is 21-hydroxylase (21-OH) deficiency –> reduced cortisol / aldosterone –> salt loss –> hyponatraemia

The lack of 21-OH –> accumulation of 17-OH progesterone and 17-OH pregnenolone instead which are precursors for androgens

20
Q

What are the clinical features of CAH?

A
  • Hyponatraemia/hyperkalaemia with volume depletion (lack of aldosterone) –> salt-losing crisis
  • [Hypoglycaemia (lack of cortisol) is uncommon]
  • Ambiguous genitalia in female neonates (not obvious in male neonates – present with salt-losing crisis and may die)
  • Growth acceleration due to extra androgens
21
Q

What is the trend for Hb after birth?

A

Decreases up to about 30 days as infant starts making HbA

22
Q

List 3 reasons for neonatal conjugated hyperbilirubinaemia.

A
  • High level of bilirubin synthesis (from rbc breakdown)
  • Low rate of transport into the liver
  • Enhanced enterohepatic circulation
23
Q

What factors make even small rises in free/unconjugated bilirubin dangerous in infants? How much conjugated bilirubin can most infants bind?

A
  1. They have low albumin (lower in prematurity) at about 34g/L - each 1g/L of albumin binds 10micromol/L of bilirubin so limit of 340micromol/L before free bilirubin is released into the bloodstream
  2. They have a leakier BBB so free bilirubin will cross more easily and cause kernicterus
24
Q

How are bilirubin thresholds for no treatment/phototherapy/exchange transfusion determined in infants?

A

NICE guidelines have charts

Preterm charts for each week available

25
Q

What are 3 other early causes of unconjugated hyperbilirubinaemia?

A
  • Haemolytic disease (ABO, rhesus, etc.)
  • G6PDD
  • Crigler-Najjar syndrome – defect in bilirubin conjugation
26
Q

Define prolonged jaundice. What are the 3 most common causes?

A
  • NICE = jaundice that lasts for >14 days in term babies and >21 days in pre-term babies
  • Causes of a prolonged jaundice:
    • Prenatal infection/sepsis/hepatitis
    • Hypothyroidism (screened at day 6-8)
    • Breast milk jaundice
27
Q

What level of conjugated bilirubin is pathological in an infant?

A

>20micromol/L - conjugated bilirubinaemia is ALWAYS pathological in an infant

28
Q

What are 3 most common causes of conjugated bilirubinaemia in an infant?

A
  • Biliary atresia (MOST COMMON; 1: 17,000)
    • 20% are associated cardiac malformations, polysplenia, situs inversus
    • Early surgery is essential (<6 months)
  • Choledochal cyst
  • Ascending cholangitis in TPN (Total Parenteral Nutrition)
    • The lipids in the TPN seem to cause an ascending cholangitis–> cBR
29
Q

Why does TPN cause conjugated hyperbilirubinaemia?

A

The lipids in the TPN seem to cause an ascending cholangitis –> cBR

30
Q

List 3 metabolic disorders which can cause conjugated hyperbilirubinaemia.

A
  • Galactosaemia - Urine reducing substances, RBC Gal-1-PUT
  • Alpha-1-anti-tryptase deficiency - Alpha-1-AT
  • Tyrosinaemia 1 - Plasma amino acids
  • Peroxisomal disease - Very long chain fatty acid profile
31
Q

How do Ca levels differ in infants? What about phosphate?

A

Ca will usually be lower so threshold for hypocalcaemia are lower (total Ca <1.8mmol/L)

Phosphate is higher in infants as they are good at reabsorbing this

32
Q

What are the clinical features of osteopenia of prematurity?

A

Fraying, splaying and cupping of long bones on XR

In long term can cause flail chest and respiratory difficulties

33
Q

Which investigations diagnose osteopenia of prematurity?

A
  1. Phosphate <1mmol/L
  2. ALP >1200U/L (which is x10 upper limit of normal in adults = osteopenia of prematurity until proven otherwise)

Calcium is normal so not useful

34
Q

What is the treatment of osteopenia of prematurity?

A
  • Phosphate/calcium supplements
  • May be given in 1-alpha calcidol
35
Q

What is the cause of rickets and how does it present?

A

Rickets = vitamin D deficiency

  • Presentation
    • Frontal bossing
    • Bowlegs/knock knees
    • Muscular hypotonia
  • Alternative presentations:
    • Tetany/hypocalcaemic seizure
    • Hypocalcaemic cardiomyopathy
36
Q

List 2 genetic causes of rickets.

A
  • Pseudo-vitamin D deficiency I (defective renal hydroxylation)
  • Pseudo-vitamin D deficiency II (receptor defect)
  • Familial hypophosphataemia
    • Low tubular maximum reabsorption of phosphate
    • Raised urine phosphoethanolamine

NB: first two may be treated with 1,25-OH vitamin D

37
Q

Which investigations can confirm rickets diagnosis?

A

Very high ALP (distinguishable by electrophoresis)

Hyperphosphatasaemia (although this can be benign and transient in infants)

38
Q

How can genetic causes of rickets be investigated?

A

1,25 OH-vitamin D levels to test for pseudo vitamin-D deficiency type I and II

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