The MRCPCH Theory and Science paper is the exam that most paediatric trainees find hardest. It tests the scientific knowledge underpinning child health — not clinical management but the mechanisms beneath it. Candidates with strong clinical skills but weaker science foundations consistently struggle because the TAS rewards a different kind of knowledge from what daily clinical practice develops.
The exam contains 95 best-of-five SBA questions in two and a half hours, with three diets per year.
Why TAS is difficult
The content spans seven distinct scientific disciplines — pharmacology, genetics, physiology, pathology, immunology, microbiology, and biochemistry — plus statistics, ethics, and research methods. Covering all of these at the required depth is a substantial undertaking, particularly for trainees who have not engaged with basic sciences since medical school.
The questions may use clinical stems, but the tested construct is always the underlying science. A TAS question about a child with cystic fibrosis asks about the CFTR gene mutation type (genetics), the chloride channel dysfunction (physiology), or the pharmacokinetics of ivacaftor (pharmacology) — not how to manage the child's respiratory exacerbation (which would be an FOP question).
Topic weighting
Pharmacology accounts for approximately 14 per cent — drug mechanisms of action (receptor pharmacology, enzyme inhibition, ion channel modulation), pharmacokinetic principles (absorption, distribution, metabolism, excretion — particularly how these differ in neonates and children versus adults), drug interactions (cytochrome P450 system), and adverse drug reactions (type A dose-dependent versus type B idiosyncratic, Rawlins-Thompson classification).
Genetics and genomics account for 14 per cent — inheritance patterns (autosomal dominant, autosomal recessive, X-linked, mitochondrial, trinucleotide repeat), chromosomal disorders (trisomy 21, Turner syndrome, Klinefelter syndrome), single gene disorders relevant to paediatrics (cystic fibrosis, sickle cell disease, Duchenne muscular dystrophy, PKU), genetic testing modalities (karyotype, FISH, microarray, exome sequencing, gene panels), and the principles of genetic counselling.
Physiology accounts for 12 per cent — cardiovascular (fetal circulation and transitional physiology, oxygen-haemoglobin dissociation curve, cardiac output determinants), respiratory (surfactant physiology, lung development, ventilation-perfusion matching), renal (GFR maturation, tubular function, acid-base regulation), and neurophysiology (pain pathways, neuromuscular junction, cerebrospinal fluid physiology).
Pathology accounts for 10 per cent — inflammation (acute versus chronic, mediators), neoplasia (oncogenes, tumour suppressors, staging principles), and organ-specific pathology mechanisms. Immunology and microbiology account for 10 per cent — innate versus adaptive immunity, immunoglobulin classes, complement system, T-cell and B-cell function, primary immunodeficiency classification, and microbiology of common paediatric infections.
Statistics and evidence-based medicine account for 8 per cent — sensitivity, specificity, positive and negative predictive values, NNT and NNH, confidence intervals, p-values, types of bias, study design hierarchy, and the ability to critically appraise a study abstract. Ethics, law, and professionalism account for 6 per cent — consent in children (Gillick competence, Fraser guidelines), safeguarding legislation, confidentiality, and research ethics.
Revision strategy
Three to four months. Start with pharmacology and genetics — they are the two largest domains (14 per cent each) and the areas where most candidates have the greatest knowledge gaps from clinical practice. Use paediatric pharmacology resources alongside question bank practice, not adult pharmacology textbooks — paediatric pharmacokinetics differ significantly from adult pharmacokinetics (different volumes of distribution, different hepatic enzyme maturation, different renal clearance rates).
Month two should cover physiology, pathology, and immunology. Month three should cover biochemistry, microbiology, statistics, and ethics. Dedicate specific sessions to statistics — NNT calculations and study design interpretation are reliably tested and reliably failed by candidates who deprioritise them.
iatroX's MRCPCH TAS bank contains over 1,500 questions mapped to the sciences curriculum. Pharmacology, genetics, and physiology are weighted to match the exam. The adaptive algorithm ensures that statistics and ethics — topics that candidates naturally deprioritise — receive proportional attention. All included at £29 per month or £99 per year.