Clin Lab - Pediatrics Flashcards
What is an alkali denaturation test (Apt test) used for?
Differentiates maternal from newborn blood in blood fetal vomit/stool/aspiration
Does fetal Hgb denature in alkaline solutions?
NO
Does adult Hgb denature in alkaline solutions?
YES
Describe the make-up of adult hemoglobin (Hb A).
2 alpha & 2 beta chains
Describe the make-up of fetal hemoglobin (Hb A).
2 alpha & 2 gamma chains
Describe the alkali denaturation test (Apt test) process.
- Sample is mixed w/ 1% NaOH & color assessed
alkali denaturation test (Apt test) (+) test for adult hgb color
- yellow-brown color
- think tea/coca cola
alkali denaturation test (Apt test) (+) test for fetal hgb color
color–>pink
NOTE on newborn screening test
All states require a set of screening tests to look for congenital d/o
Major types of congenital newborn screenings?
- Congenital heart dz
- Hearing test
- Genetic d/o
What are the types genetic disorders screened in newborns?
- Errors of metabolism
- Hormone disorders
- Hemoglobinopathies
- Immune deficiencies
- other
Describe congenital heart dz screening.
Screens for critical congenital heart issues that cause hypoxemia & likely will need correction emergently or w/n 1st year of life
Examples of congenital heart dz?
- Tetralogy of Fallot
- Transposition of the great arteries
- Correction of the aorta
- Tricuspid or pulm atresia
When will hypoxemia likely become apparent?
O2 sats < 80%
What does the typical testing algorithm for congenital heart dz start with?
Test O2 sat using right hand & either foot
Why test the right hand & either foot?
Looking a perfusion (if coarctation we’re looking on above and below)
What is the timing go the newborn screenings?
- Initial screen >/= 24hrs after birth
- repeat screen at 1hr & 2hrs
Why is the initial new born screening measured >/= 24hrs after birth?
Babies can have normal transient hypoxemia
Positive screening test if any of the following are met:
- O2 < 90% in either extremity at any reading
- O2 90-94% in BOTH extremities on all 3 measurements
- O2 difference > 3% b/t extremities on all 3 measurements
If a newborn meets 1 of the criteria for a (+) screening for coarctation, does this mean they have it?
NO
If a (+) screening test for congenital heart dz, what happens next?
pediatric cardiology evaluation
- Need to also rule out causes of hypoxemia
What labs are done to rule out causes of hypoxemia?
- CXR
- CBC
- CMP
What imaging would look at the heart for a coarctation?
Echo
When should newborn tearing screening test be performed?
around 24hrs
What are the 2 types of hearing test for a newborn screening?
- Otoacoustic emissions (OAE)
- Automated auditory brainstem response (AABR)
Describe Otoacoustic emissions (OAE).
microphone placed in the ear canal detects sound waves generated in cochlea
Describe an automated auditory brainstem response (AABR)
sensors placed on head and neck detect action potentials in auditory nerve
Which type of hearing test is used in high risk newborns?
Automated auditory brainstem response (AABR)
Describe the 2 step screening for hearing issues.
Initial screen
- If (-), no further eval; monitor periodically at well child checkups
- If (+), repeat screening test in a few hrs
–> If (-) on 2nd screen, assume (-) but monitor closely
–> If (+) on 2nd screen, refer to audiologist
What are inborn disorders looking for on newborn screening?
abnormal level(s) of metabolites/ hormones/immune markers
How is the sample for testing obtained for inborn d/o?
blood from heel stick applied to test papers & sent to state labs.
When is the sample obtained for inborn d/o? Why?
close to discharge to allow max accumulation of markers
If the inborn d/o test is (+), what’s next?
will need further testing
List types of inborn d/o.
- Errors of metabolism
- Congenital hormonal disorders
- Hemoglobinopathies
- Immunodeficiencies
- Other genetic disorders
What are the results of an error of metabolism?
- accumulation of intermediate substance
- product def or
- toxic metabolite
What is an example of a dz cause by an error of metabolism?
Maple syrup urine dz
Pathophys of maple syrup urine dz.
- enzyme def in pathway that breaks down BCAA (leucine, isoleucine, valine).
- toxic metabolites cause distinctive smell of maple syrup in cerumen, urine, sweat
Errors of metabolism NOTE
Rare but serious genetic disorders
List the 4 categories of errors of metabolism.
- AA d/o
- CHO d/o
- Organic acid d/o
- FA d/o
Examples of amino acid d/o
- Phenylketonuria (PKU)
- Maple syrup urine disease
- Homocystinuria
Testing for amino acid d/o
serum AA levels
Examples of CHO d/o
- Galactosemia
- Glycogen storage dz
Testing for CHO d/o
serum CHO levels
Examples of organic acid d/o
- Propionic acidemia
- Methylmalonic acidemia
Testing for organic acid d/o
serum levels
What tends to occur w/ organic acid d/o?
metabolic acidosis w/ presenting sign of tachypnea
Examples of FA d/o
acyl-CoA dehydrogenase deficiencies
Testing for FA d/o
serum levels
Describe genetic penetrance
It is the severity of the condition
- lower penetrance = takes longer for substance to accumulate
- higher penetrance = take less for substance to accumulate
Possible lab findings of acute decompensation w/ errors of metabolism
- metabolic acidosis
- Hyperammonemia
- abnl LFTs
- -cytopenias from bone marrow suppression
- hypoglycemia
- elevated LDH
- elevated CPK
Describe labs findings for metabolic acidosis when acute decomposition in errors of metabolism.
- organic acid d/o
- low CO2 & HAGMA (adding an acid) on BMP
- Order ABG to prove
Describe Hyperammonemia & S/Sx.
Result of ammonia (think encephalopathy)
- lethargy poor feeding
- irritable
- restless