SN7 SHORT NOTE 5M ★ High-yield

Describe the principles of biochemical screening with examples in the newborn and in pregnancy.

Biochemistry · 1st Professional — Pre-Clinical

Definition

Screening = the presumptive identification of unrecognised disease in apparently healthy individuals, by tests that can be applied rapidly and cheaply to large numbers.

Criteria for a Screening Programme (wilson and Jungner)

The condition should be an important health problem
Its natural history must be understood, with a recognisable latent or early symptomatic stage
A suitable test must exist — simple, safe, acceptable, sensitive and specific
An accepted treatment must be available, and early treatment must improve the outcome
Facilities for diagnosis and treatment must be available
The programme must be cost-effective and continuing, not a one-off

CLINICAL PEARL

The most important criterion is that early treatment changes the outcome. Detecting a disease earlier is worthless, and may be harmful, if nothing useful can be done sooner. This is the argument at the centre of the controversy over PSA screening.

Biochemical Screening in the Newborn

Condition	Test	Why it matters
Congenital hypothyroidism	TSH on day 3–5	Treatment within 2 weeks prevents retardation entirely
Phenylketonuria	Guthrie test or tandem MS, after 48–72 h of milk	Diet prevents irreversible mental retardation
Congenital adrenal hyperplasia	17-hydroxyprogesterone	Prevents salt-wasting crisis and death
G6PD deficiency	Fluorescent spot test	Avoids drug-induced haemolysis and kernicterus
Galactosaemia	GALT assay	Diet prevents liver damage, cataract and sepsis
Sickle cell disease	Haemoglobin electrophoresis or HPLC	Penicillin prophylaxis reduces mortality
Biotinidase deficiency	Enzyme assay	Biotin prevents deafness and optic atrophy

Tandem mass spectrometry detects over 30 disorders from one dried blood spot — the modern basis of expanded newborn screening
India screens for congenital hypothyroidism, CAH and G6PD deficiency in many centres, though coverage remains incomplete

Antenatal Biochemical Screening

Test	Timing	Detects
Double marker — free β-hCG, PAPP-A	11–13 weeks	Down syndrome, trisomy 18
Triple marker — AFP, hCG, unconjugated oestriol	15–20 weeks	Down syndrome, neural tube defects
Quadruple marker — adds inhibin A	15–20 weeks	Better detection rate
Cell-free fetal DNA	From 10 weeks	Non-invasive; very high detection rate
Oral glucose tolerance test	24–28 weeks	Gestational diabetes

Raised AFP suggests a neural tube defect; low AFP with low oestriol and high hCG suggests Down syndrome
Screening tests give a risk, not a diagnosis — a positive result requires confirmation by amniocentesis or chorionic villus sampling

Screening in Adults

Diabetes — fasting glucose or HbA1c in those over 30 or with risk factors; important given India's burden
Dyslipidaemia — lipid profile for cardiovascular risk assessment
Chronic kidney disease — urine albumin:creatinine ratio in diabetics and hypertensives
Anaemia — haemoglobin in women and children
Thyroid — TSH in pregnancy and in the elderly

Applied Aspects

One book of nineteen in the KAVACH series · mbbsadda.in

All questions in Clinical & Applied Biochemistry

Every Biochemistry chapter →