Special Consideration for Children
Most assays can be performed on small sample volumes for children. Special containers for collecting blood from finger pricks may be obtained from the laboratory. Please phone the laboratory for advice about sample requirements.
Finger-prick or venous sample?
Many assays can be analysed from finger prick samples rather than formal venepunctures. These are easier for the clinician to obtain and probably kinder for the child when only small quantities of blood are required. Finger prick samples are routinely used for estimation of Haemoglobin A1c in diabetic children and in children in whom it is impossible to obtain blood by other means. The process of massaging the pulp of the finger to increase the flow of blood results in a degree of tissue damage and the consequent release of extra vascular tissue fluid and cellular contents which invalidates the estimation of plasma electrolytes and enzymes eg AST & LDH.
Reference ranges, as quoted on result forms, usually refer to adult populations. The ranges for many analytes differ during childhood and adolescence. These are usually printed on the report form provided that the age and sex of the child was given on the request form.
Creatinine reflects the mass of muscle and will therefore increase as a child grows; normal neonates have creatinine concentrations of about 20-30 mmol/L and these values increase to 70-120 mmol/L in the late 'teens in proportion to muscle development.
Alkaline phosphatase reflects bone growth. It has therefore relatively high concentration during the first year of life and then falls until the growth spurt during puberty. High concentrations will also occur after bony fractures (and during pregnancy).
Immunoglobulins change throughout childhood according to age and sex.
Proteins increase by approximately 10% from infancy to adulthood.
Neonatal screening & investigation of inborn errors of metabolism
See Biochemical Genetics section.
Acute poisoning is clearly an emergency situation requiring hospital care. Confirmation of more long- standing poisoning may be performed on a random urine sample (20-40 mL). Please discuss such requests with the laboratory in advance.