The filter paper used for specimen collection may vary, but a common system has a sheet of filter paper with 5 half inch circles, each of which must be filled. Normally each circle is filled by applying a large drop of blood once to the center of the circle.
Categories of failure:
(1) timing
(2) collection of the blood onto the filter paper
(3) storage and transportation
(4) therapeutic interventions
The specimens are usually collected before the neonate is discharged from the hospital. With a trend towards shorter admissions, infants may be discharged within 48 hours of delivery. Some metabolic conditions require a period of time before sufficient target material accumulates to be detected. A neonate discharged before this time period has passed must have a second specimen collected from 48 hours to 10 days after delivery.
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Condition
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Time Period for Specimen After Delivery
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hypothyroidism
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> 24 hours
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phenylketonuria
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>= 48 hours
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homocystinuria
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>= 48 hours
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Specimen collection onto filter paper:
(1) no blood specimen collected
(2) not all required circles filled
(3) circles not completely filled
(4) too much blood is applied (supersaturated)
(5) blood appears to be scratched or abraded
(6) specimen appears diluted
(7) specimen appears discolored or contaminated
(8) specimen shows serum rings
(9) specimen is smeared, layered or clotted
(10) specimen applied to both sides of the filter paper
(11) hemolysis from excessive pressure (squeezing, milking) during collection
Storage and transportation:
(1) not dried adequately (3-4 hours with card lying flat)
(2) storage in direct sunlight or next to heat
(3) storage in humid environment, including a sealed plastic bag
(4) delayed transport to testing laboratory (should be shipped within 24 hours of collection and received by 10 days after collection)
(5) improperly stacking multiple filter papers
Therapeutic interventions:
(1) blood transfusion
(2) dialysis
