Metabolic & Genetics — free preview
Question 1 of 2
Reference values
Typical paediatric values. A real laboratory quotes its own ranges, and several of these move with age.
Vital signs by age
| Age | Heart rate | Respiratory rate | Systolic BP — hypotension below |
|---|---|---|---|
| Term newborn | 110–160 | 30–40 | 60 mmHg |
| 1–12 months | 110–160 | 30–40 | 70 mmHg |
| 1–2 years | 100–150 | 25–35 | 70 + (2 × age) mmHg |
| 2–5 years | 95–140 | 25–30 | 70 + (2 × age) mmHg |
| 5–12 years | 80–120 | 20–25 | 70 + (2 × age) mmHg |
| Over 12 years | 60–100 | 15–20 | 90 mmHg |
Other bedside measures
| Measure | Reference | Note |
|---|---|---|
| Temperature | 36.5–37.5 °C | 38.0 or above is fever |
| Oxygen saturation | 94–100 percent in air | under 92 in air needs oxygen and admission |
| Capillary refill | under 2 seconds | 3 seconds or more suggests shock |
| Heart rate | see the table above | age dependent |
| Respiratory rate | see the table above | age dependent |
| Blood pressure | see the table above for the hypotension floor | hypertension: systolic over roughly 105 mmHg at 1–2 y, 112 at 2–5 y, 118 at 5–12 y, 130 over 12 y |
| Ejection fraction | 55–70 percent | under 40 percent is systolic failure |
| Valve gradient (echo) | mean gradient under 25 mmHg is mild; 25–40 moderate; above 40 severe | for aortic stenosis – the peak instantaneous gradient reads higher than the mean, so check which one is quoted |
| Troponin | below the assay cut-off in a well child | a rise means myocardial injury, most often myocarditis in this age group |
Arterial blood gas
| Measure | Reference | Note |
|---|---|---|
| pH | 7.35–7.45 | |
| PaCO2 | 35–45 mmHg (4.7–6.0 kPa) | the respiratory term |
| PaO2 | 80–100 mmHg (10.6–13.3 kPa) | breathing room air |
| Bicarbonate | 22–26 mmol/L | the metabolic term |
| Base excess | −2 to +2 mmol/L | |
| Lactate | under 2 mmol/L | over 4 marks shock |
| A–a gradient | under 10–15 mmHg in air | a normal gradient means the lungs are not the problem |
Lung function and body fluids
| Measure | Reference | Note |
|---|---|---|
| FEV1 / FVC | FEV1 80 percent or more of predicted; ratio above 0.85 in children | asthma severity is graded on FEV1 off treatment: 80+ mild, 60–80 moderate, under 60 severe |
| Bronchodilator reversibility | a rise of 12 percent or more in FEV1 | this is what makes obstruction reversible, and it is the asthma test |
| Pleural fluid – exudate | protein above 30 g/L (3 g/dL), or fluid to serum protein above 0.5; LDH ratio above 0.6 | pH 7.2 or below, glucose under 2.2 mmol/L, or frank pus means it needs a drain |
| Dehydration | 5 percent mild, 10 percent moderate, 15 percent severe | estimated clinically – each 1 percent is 10 mL/kg of deficit |
Haematology
| Measure | Reference | Age note |
|---|---|---|
| Haemoglobin | see age note | newborn 14–22 g/dL; physiological nadir 9.5–13.5 at 6–9 weeks; 6 months to 6 years 10.5–14; 6–12 years 11.5–15.5 |
| White cells | see age note | newborn 9–30 ×109/L; 1 year 6–18; 4–10 years 4–13.5; adolescent 4.5–11 |
| Neutrophils | neutropenia under 1.5 ×109/L, severe under 0.5 | |
| Lymphocytes | see age note | the lymphocyte and neutrophil lines CROSS twice: lymphocytes predominate from about 1 week to 4 years, neutrophils either side of that |
| Eosinophils | under 0.5 ×109/L, or under 5 percent | |
| Platelets | 150–450 ×109/L | |
| MCV | lower limit roughly 70 + age in years (fL) | to about 12 years |
| ESR | under 10–20 mm/h | |
| CRP | under 5–10 mg/L | laboratory dependent |
Anaemia and coagulation tests
| Measure | Reference | Note |
|---|---|---|
| Ferritin | 15–150 µg/L (ng/mL) | a low value proves iron deficiency, but it is an acute phase protein, so a normal one during infection or inflammation does not exclude it |
| Serum iron / transferrin saturation | saturation under 16 percent suggests iron deficiency | iron is low in both iron deficiency and anaemia of chronic disease; the iron binding capacity is high in the first and low in the second |
| Reticulocyte count | 0.5–1.5 percent | high means the marrow is responding, as in haemolysis or blood loss; low with anaemia means the marrow is the problem |
| Haematocrit | newborn 45–65, child 33–43 percent | above 65 percent in a newborn is polycythaemia |
| Prothrombin time / APTT | PT 11–14 s, APTT 25–38 s | an isolated long APTT with normal platelets suggests haemophilia; both prolonged suggests vitamin K deficiency, liver disease or consumption |
| Factor VIII / IX activity | 50–150 percent of normal | severe disease is under 1 percent, moderate 1–5, mild 5–40 |
| Fibrinogen | 1.5–4.0 g/L | falls in consumption; it is also an acute phase protein, so a normal value during sepsis may already represent a fall |
| D-dimer | raised in consumption and in thrombosis | infection and inflammation raise it too, so a high value is not specific |
| Haemoglobin electrophoresis | HbA2 under 3.5 percent, HbF under 2 percent beyond infancy | HbA2 above 3.5 percent identifies beta thalassaemia trait; it is falsely lowered by coexisting iron deficiency |
| Haptoglobin / LDH | haptoglobin falls and LDH rises in haemolysis; LDH roughly under 300 U/L in a well child | read them beside the reticulocyte count and the bilirubin. LDH is also a bulk-of-disease marker in leukaemia and lymphoma and rises in tumour lysis |
| Direct antiglobulin test | negative in a healthy child | a positive test means antibody is bound to the red cells, which separates immune haemolysis from every other kind |
Electrolytes and renal
| Measure | Reference | Note |
|---|---|---|
| Sodium | 135–145 mmol/L | |
| Potassium | 3.5–5.0 mmol/L | up to 6.0 in the newborn |
| Chloride | 98–107 mmol/L | |
| Bicarbonate | 22–26 mmol/L | same value as on the gas |
| Urea | 2.5–6.5 mmol/L (7–18 mg/dL) | |
| Creatinine | infant 15–35, child 25–60, adolescent 50–90 µmol/L | rises with muscle mass, so an adult range over-reads a child |
| Glucose | 3.5–5.5 mmol/L (63–99 mg/dL) | newborn above 2.6 mmol/L |
| Urine sodium / chloride | under 20 mmol/L means the loss is not renal | a high urine chloride points to the kidney or a diuretic |
Liver, bone and metabolic
| Measure | Reference | Note |
|---|---|---|
| ALT / AST | 10–40 / 10–45 U/L | |
| GGT | 5–35 U/L | up to 200 in the first months of life |
| Alkaline phosphatase | child 100–400 U/L, higher in the growth spurt | an adult range makes normal childhood bone turnover look like disease |
| Bilirubin (total) | under 17 µmol/L (1 mg/dL) beyond the newborn period | |
| Conjugated bilirubin | under 17 µmol/L, or under 20 percent of total | above this is always pathological |
| Albumin | 35–50 g/L | |
| Cholesterol / triglycerides | total cholesterol under 4.4 mmol/L, triglycerides under 1.5 mmol/L | both rise steeply in nephrotic syndrome, in proportion to the albumin loss |
| Total protein | 60–80 g/L | albumin plus globulin – a low total with a low albumin points to loss rather than to synthesis |
| INR / prothrombin time | INR 0.8–1.2 | the earliest measure of failing liver synthesis, and it does not correct with vitamin K once the liver is the problem |
| Creatine kinase | under 200 U/L | thousands mean muscle: a Duchenne CK runs 10 000 to 20 000 from infancy |
| Ammonia | newborn under 110, child under 50 µmol/L | |
| Calcium / magnesium / phosphate | 2.2–2.7 / 0.7–1.0 / 1.2–2.0 mmol/L | phosphate runs higher in infancy, to about 2.6 |
| Lipase or amylase | three times the upper limit defines pancreatitis | |
| Sweat chloride | under 30 normal, 30–59 intermediate, 60 or more diagnostic | |
| Caeruloplasmin | 0.2–0.6 g/L | low in Wilson disease, and it is an acute phase protein, so a normal level during inflammation does not exclude it |
| Parathyroid hormone | 1.6–7.5 pmol/L | rises early in chronic kidney disease, before calcium or phosphate move |
| Antistreptolysin O titre | under 200 IU/mL in most children | peaks 3–6 weeks after a streptococcal throat infection; a single raised value shows exposure, not active disease |
| Malaria parasitaemia | any level is abnormal | above 2 percent counts as severe in a non-immune child, and above 10 percent is an indication for exchange transfusion in some protocols |
Endocrine and hormones
| Measure | Reference | Note |
|---|---|---|
| Thyroid stimulating hormone | 0.5–5.0 mIU/L beyond the newborn period | it surges to 20 or more in the first days of life, so a newborn screen is read against its own threshold and not against this range |
| Free T4 | 12–22 pmol/L | a low free T4 with a high TSH is primary hypothyroidism; a low free T4 with a low or normal TSH points to the pituitary |
| Cortisol | morning 140–500 nmol/L | the value only means something beside the time and the clinical state: under 100 during hypoglycaemia or shock is inappropriately low |
| ACTH | 2–11 pmol/L (10–50 ng/L) | high with a low cortisol is adrenal failure; high with a high cortisol points above the adrenal |
| 17-hydroxyprogesterone | under 10 nmol/L after the first few days | grossly raised in 21-hydroxylase deficiency, and the newborn screening analyte for congenital adrenal hyperplasia |
| Growth hormone / IGF-1 | a random growth hormone is uninterpretable; peak over 7 µg/L on provocation is normal | IGF-1 is read against age and pubertal stage, and is low in malnutrition as well as in deficiency |
| LH / FSH | prepubertal under 0.3 IU/L | an LH above 0.3 with a pubertal response to stimulation means the axis has switched on, which is what separates central from peripheral puberty |
| Testosterone / oestradiol | prepubertal testosterone under 0.5 nmol/L, oestradiol under 20 pmol/L | |
| HbA1c | under 42 mmol/mol (6.0 percent) | 48 mmol/mol (6.5 percent) or more is diagnostic of diabetes; it is unreliable when red cell survival is shortened |
| Insulin / C-peptide | should be undetectable when glucose is low | any measurable insulin during a hypoglycaemic episode is abnormal and is the whole diagnosis in hyperinsulinism |
| Ketones (blood) | under 0.6 mmol/L | 3.0 or more with acidosis defines ketoacidosis; absent ketones during hypoglycaemia is the abnormal finding, not a reassuring one |
| 25-hydroxyvitamin D | sufficient above 50, deficient below 25 nmol/L | this is the storage form and the one to measure; the active 1,25 form can be normal or high in nutritional rickets |
| Plasma metanephrines | any clear elevation is abnormal | the screening test for a catecholamine-secreting tumour; caffeine and several drugs raise it falsely |
| Renin / aldosterone | both read against sodium intake and posture | renin rises in salt-losing states and is suppressed when mineralocorticoid excess is driving the blood pressure |
Metabolic screening
| Measure | Reference | Note |
|---|---|---|
| Anion gap | 8–16 mmol/L | sodium minus chloride and bicarbonate. Above 16 means an unmeasured acid: lactate, ketones, an organic acid or a toxin |
| Uric acid | 0.12–0.35 mmol/L (2–6 mg/dL) in children | high in tumour lysis, renal failure and several inborn errors; low in molybdenum cofactor deficiency |
| Plasma phenylalanine | under 120 µmol/L | the newborn screening analyte; treatment is started above about 360 µmol/L and the level guides dietary control |
| Plasma amino acids / urine organic acids | qualitative | the PATTERN names the disorder rather than any single value, and the sample must be taken during the acute illness to be interpretable |
Tumour markers
| Marker | Reference | Note |
|---|---|---|
| Alpha-fetoprotein | adult and child under 10 ng/mL (under 8 kU/L) | very high at birth and falls to the adult range by about 8 months, so a neonatal value must be read against age; raised in hepatoblastoma, yolk sac tumour and germ cell tumours |
| Urinary catecholamines | homovanillic and vanillylmandelic acid, reported against urinary creatinine | raised in about nine in ten neuroblastomas, which is why the urine test comes before any biopsy |
Immunology and coeliac serology
| Measure | Reference | Note |
|---|---|---|
| Total IgA | see age note | 1–3 years 0.2–1.0, 4–6 years 0.3–1.3, school age 0.5–2.0, adult 0.8–3.0 g/L. Selective IgA deficiency is under 0.07 g/L |
| IgG / IgM | IgG 5–16 g/L, IgM 0.5–2.0 g/L beyond infancy | IgG falls to a physiological trough at 3–6 months as maternal antibody clears |
| Tissue transglutaminase IgA | negative under 7 U/mL; 10x the upper limit supports coeliac disease | it is an IgA antibody, so it reads falsely negative when total IgA is low – always check the total IgA beside it |
| C3 / C4 | C3 0.75–1.65 g/L, C4 0.14–0.54 g/L | a low C3 that recovers by 8–12 weeks is post-infectious nephritis; one that stays low beyond that points to C3 glomerulopathy or membranoproliferative disease, and a low C4 alongside it suggests lupus |
Cerebrospinal fluid
| Measure | Newborn | Child |
|---|---|---|
| White cells | 0–20 /mm3 | 0–5 /mm3 |
| Protein | 0.4–1.2 g/L | 0.15–0.45 g/L |
| Glucose | at least 60 percent of the blood glucose | at least 60 percent of the blood glucose |
| Bacterial pattern | hundreds to thousands of neutrophils, high protein, low glucose | same |
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What this deck covers
Metabolic and Genetic Disorders – Exam Review Set 1 in 50 board-style clinical cases with worked explanations. Each case gives you a clinical vignette, four options, the correct answer, and an explanation of why each of the other three is wrong, with the guideline or textbook it follows named on the answer.
Board-style teaching questions for paediatricians and trainees preparing for paediatric board, MRCPCH and licensing examinations. Written from published guidelines and standard paediatric textbooks, with the source named on every answer.
The 50 cases, in order
- Different doors, same room
- One cause, many faces
- Measure the enzyme itself
- A clean result that proves little
- Where the gene sits
- The outsider on this list
- Look in the cupboard
- Nothing to feel in the belly
- Dark on standing
- Too little cholesterol
- Give back what is missing
- A long gap to cover
- The number that goes up
- Forty-five, and perfectly well
- Big baby, big tongue
- What the Y changes
- Ask how they are related
- What the drug takes with it
- The vessel, not the lens
- A boy with a webbed neck
- Very sociable with a heart murmur
- Floppy first, then always hungry
- Only the mothers pass it on
- What the short father passes on
- Younger in every generation
- Big ears and a long face
- A carrier mother’s children
- Cousins asking about risk
- Overlapping fingers at birth
- Cleft, extra digits and scalp defects
- Blue on feeding, pink on crying
- One small side of the face
- A tumour on the optic pathway
- Tremor with a bad liver
- Small jaw, strong glasses
- Severe pain and a soft belly
- Twisted hair and seizures
- Cataracts, floppy and rickets
- Diabetes, deafness and failing sight
- Strokes at twelve with deafness
- Fits, rash and no hair
- Both alleles speaking at once
- Planning the next pregnancy
- No speech and happy laughter
- A small jaw and a blocked airway
- Fingers, weight and the dark
- Floppy with a huge heart
- Floppy from the first day
- Off the diet and expecting
- Forty-six, not forty-seven
Diagnoses and management options tested
Across the fifty cases you are asked to choose between options such as: Incomplete penetrance, That the urine screen is definitive, Magnesium containing antacids, Trisomy 13, A twin pregnancy, Annual ultrasound of the ovaries, A clot, arterial or venous, A trinucleotide repeat expansion, Anticipation, Autosomal recessive conditions, Down syndrome, The fibrillin gene on chromosome 15, Wilson, A mitochondrial disorder.
Clinical pearls from this deck
- Two affected parents with unaffected children is not a paternity question. It is usually two different genes reaching the same outcome.
- When one gene reaches three organs, the referral that found it is never the whole assessment.
- Stop the lactose on suspicion and send the enzyme afterwards. The screen tells you to act; only the enzyme tells you what it is.
- A normal enzyme result excludes an enzyme, not a family of diseases. Ask which enzyme was measured before you accept any reassurance.
- Remember the arm, not just the number. Getting it wrong turns a one in four recessive conversation into an X-linked one.
- Optic atrophy in a child with diabetes is not retinopathy until someone has thought about Wolfram.
Work through the deck once for recognition, then again a week later to test yourself — each question gives the answer and explains why every other option fails.
More from this system: all metabolic & genetics case decks · pediatric reference values.
