ChemPath - Paediatric Clinical chemistry Flashcards
What are the common problems in LBW babies
Respiratory distress syndrome (lack of surfactant in the lungs, common <34w)
Retinopathy of prematurity (An abnormal growth of blood vessels in the eye → vision loss )
Intraventricular haemorrhage
Patent ductus arteriosus
Necrotising enterocolitis
What is necrotising enterocolitis and how does it present
Inflammation of the bowel wall → necrosis and perforation
Symptoms = bloody stools, abdominal distension, intramural air
Describe the development of the kidney in infants and when is GFR maturity reached
Nephrons start to develop from week 6 → produce urine from week 10 → full complement from week 36
Functional maturity of GFR is not reached until 2 years of age
Describe the glomerulus in infants
Large surface area: volume ratio (relatively low GFR for their surface area) which leads to:
- Slow excretion of solute load
- Limited amount of Na+ available for H+ exchange - susceptible to acidosis
Describe the proximal convoluted tubule in infants
Short PCT: lower resorptive capability (but usually adequate due to a small load)
Reabsorption of bicarbonate is also not as effective (propensity to acidosis)
Renal threshold for glycosuria is much lower in neonates i.e. glycosuria appears at a lower plasma glucose level in neonates
Describe the loop of Henle and distal convoluted tubule in infants
The LoH/DCT are short - reduced concentration ability
Their DCT is relatively unresponsive to aldosterone (despite fully developed RAAS) → persistent loss of sodium + increased potassium retention
Describe fluid balance in infants
In utero = more ECF
After birth → pulmonary resistance decreases → ANP release → re-distribution
All babies can lose up to 10% in the first week of life due to fluid shifts
What is the difference in electrolyte requirements in infants vs adults
5x more fluid
3.5x more sodium (higher if <30 weeks)
2x more potassium
What are the causes of insensible (uncontrollable) water loss in infants
High surface area
High skin blood flow
High metabolic/respiratory rate
High transepidermal fluid loss (skin is not keratinised in premature infants)
Which drugs used in infants may lead to electrolyte disturbance
Bicarbonate - contains high sodium
Antibiotics - contains high sodium
Caffeine/theophylline - increases renal sodium loss
Indomethacin - oliguria
What are the causes of hypernatraemia in infants
More common in the first 2 weeks, if >2 weeks may be due to dehydration
Salt poisoning
Osmoregulatory dysfunction
What are the causes of hyponatraemia in infants
4-5 days: Excess total body water due to excessive intake, SIADH secondary to infection (pneumonia, meningitis) or IVH
After 4-5 days: Sodium loss due to immature tubular function in patients on diuresis
Factitious: Na is normal but appears low
Congenital adrenal hyperplasia
What is congenital adrenal hyperplasia
Most common cause is 21-hydroxylase (21-OH) deficiency → reduced cortisol / aldosterone → salt loss
+ accumulation of 17-OH progesterone and 17-OH pregnenolone → produce high levels of androgens
Identified on Gurthrie spot
What are the clinical features of congenital adrenal hyperplasia
Hyponatraemia/hyperkalaemia with volume depletion (lack of aldosterone) → salt-losing crisis
Hypoglycaemia (lack of cortisol)
Ambiguous genitalia in female neonates (not obvious in male neonates – present with salt-losing crisis)
Growth acceleration
What are the reasons for neonatal hyperbilirubinaemia in the first 10 days of life
High level of bilirubin synthesis (due to reduction in HbF)
Low rate of transport into the liver
Enhanced enterohepatic circulation
What is the risk of free bilirubin that is not bound to albumin
Free bilirubin crosses the BBB and can cause kernicterus (bilirubin encephalopathy)
Higher risk in premature babies who have lower albumin
What is the treatment for hyperbilirubinaemia
Phototherapy (>350 term, >120 prem)
Exchange transfusion (>450 term, >230 prem)
What are the causes of hyperbilirubinaemia in the first 24h
Haemolytic disease (ABO, rhesus, etc.)
G6PDD
Crigler-Najjar syndrome
What is the definition of prolonged jaundice
jaundice that lasts for >14 days in term babies and >21 days in pre-term babies
What are the causes of prolonged jaundice
Prenatal infection/sepsis/hepatitis
Hypothyroidism (screened at day 6-8)
Breast milk jaundice
What are the causes of conjugated hyperbilirubinaemia
Biliary atresia (MOST COMMON; 1: 17,000) - 20% are associated cardiac malformations, polysplenia, situs inversus
Choledochal cyst
Ascending cholangitis in TPN (Total Parenteral Nutrition) - thought to be lipids
Inherited metabolic diseases:
- 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)
What is the normal calcium and phosphate handling in infancy
Calcium and PO4 are laid down in the LAST trimester
After birth, all babies’ calcium will fall (lower than adults)
Phosphate is higher in babies as they are good at reabsorbing phosphate
Describe osteopenia of prematurity and its biochemical features
fraying, splaying and cupping of long bones
Calcium NORMAL
Phosphate is <1 mmol/L (often first sign)
ALP >1200 U/L (10 x adult ULN)
What is the treatment for osteopenia of prematurity
Phosphate/calcium supplements
1-alpha calcidol
What are the clinical features of Rickets
Frontal bossing
Bowlegs/knock knees
Muscular hypotonia
Tetany/hypocalcaemic seizure (emergency)
Hypocalcaemic cardiomyopathy
What are the genetic causes of rickets
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
