Neonatal screen - dried blood spot

Last updated: Friday, 19, March, 2004

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Item Process
Specimen

Blood absorbed onto special paper at 4 days of age, or at discharge (if earlier than 4 days).

Method

Diseases commonly screened for include:

Phenylketonuria: phenylalanine (Guthrie bacterial inhibition assay, fluorometry,mass spectrometry);
Hypothyroidism: TSH (immunoassay);
Cystic Fibrosis: trypsin(ogen) (immunoassay), mutation genotyping (molecular genetics: PCR based identification);
Galactosaemia: galactose-1-phosphate, galactose (fluorometry).

Reference Interval

Varies with method.

Cut off value is set at an appropriate figure to avoid false negatives.

Application

Population screening for severe, treatable diseases (usually phenylketonuria, hypothyroidism, cystic fibrosis, galactosaemia).

Interpretation

Positive results require follow-up for definitive diagnosis.

False negatives are very rare.

Hypothyroidism due to hypopituitarism is not detected by a TSH screen, but the clinician is usually alerted to this possibility by clinical signs of intracranial disease.

Reference

Brown ARD. Clin Biochem Revs 1985; 6: 3-13.