Clinical Chemistry

Maximal absorbance of bilirubin

Specimen requirements?

450nm

minimal blood contamination, protect from light

Degree of fetal hemolysis

whict test?

Amniotic fluid bilirubin

–> serial measurements ~ estimated GA

hCG methodology

= Glycoprotein –> a-subunit –> TSH,FSH.LH

–> beta-subunit–> immunoassay

false – hCGurine

Causes?

Dilute urine

Hook effect

–> confirm with hCGserum

false + hCGserum

Cause?

heterophile Ab interference

–>repeat on different analyzer/pretreat w heterophile binding reagent/run serial dilutions

low level “phantom” hCG

No a/w pregnancy or overt gestational trophoplastic disease – Causes & Rx

1. Pt w appropriately treated GTD

2. ~incidental, rare–> pituitary tm

Rx: none if no anatomic lesion is identified

hCG in normal pregnancy

Detectable – when?

Plateaus- when?

6-8 wks post conception ~ implantation

early 2nd trimester – plateaus @ 10,000 ( 800ng/ml)

*end of 1st trimester = 100,000 

hCG remains detectable for how long after?

1.delivery

2. spontaneous abortion

3.evacuation of uncomplicated molar pregnancy

1. 2wks –> triphasic

2. 4-6 wks

3. 10 wks

Female with abdominal pain / mild vaginal bleeding

hCGserum <66% in 48hrs

DDx

Ectopic1 / spontaneous abortion

115% –Normal rate of rise

15% of normal IUP–> abnormal rate of rise

Clinical: Uterine enlargement out of proportion for GA

vaginal bleeding, HTN, absence of fetal heart tones

hCG >> normal -Dx?

Complete mole–>risk of malignancy 20%(Partial–>5%)

hCGcomplete> hCGpartial

Clinical –> Complete”

Uterine choriocarcinomas and molar pregnancy

50% –> post normal term pregnancy

25% –>post histologically normal spontaneous abortion

25% –> molar pregnancy

Prenatal screening for Trisomy and neural tube defect

1.[hCG,AFP & unconj Estriol]1maternal serum~ 18wks (Sens=70%)

2.”Quad test” =1 + dimeric inhibin A –>stable in 2nd Trim (Sens=80%)

1affected by inaccurate GA estimation

3. “Integrated screen” PAPP-A&hCG 1st trim,AFP, uE & DAI 2nd trim

mild decrease in uE & hCG
diabetic mother

– decrease in uE & hCG

– increase in AFPmaternal

mothers who smoke

decrease AFP, hCG,uE

dx?

Trisomy 18 (Edward syndrome)

“Edward = 18 –> vampire”

increased AFP, MSAFP1

nml hCG

decreased uE – Dx?

Neural tube defect

1twin gestation

increased hCG

decreased AFP & uE

Dx?

Trisomy 21

Also–> elevated dimeric inhibin A

Principle plasma protein in the fetus

AFP

MSAFP–> ~ maternal weight, race, # of fetuses, maternal diabetes

Test for assessing the risk of preterm labor

Estriolserum/salivary –> increse prior to the onset of preterm labor

bacterial vaginosis

Fetal fibronectin, transvaginal cervical U/S

Fetal fibronectin

Positive and negative predictive value

Causes of false elevation

PPV = low , NPV = high

specimen collection<24hrs s/p cervical exam/intercourse

Best specimen for fetal lung maturity determination

Uncontaminated amniotic fluid

–> GA 34-37 wks

Lecithin/sphingomyelin ratio (normal 2:[email protected] wks)

problems in interpretation

DM –> phosphatidylglycerol –> more reliable

Meconium –> decreases L:S ratio

Blood –> normalizes L:S to 1.5

CV of L:S –> high

Fluorescence polarization assay–> rapid test w lower CV

Contaminated amniotic fluid

Tests of choice for determination of lung maturity

[Phosphatidylglycerol]–> first detected @ 36 wks

[disaturated phosphatidylcholine]=lecithin major component 

Lamellar body number density

Method of measurement

Surfactant lamellar bodies ~> size of platelets

=> cell counter platelet channel

>50,000/mL => lung maturity

Physiologic changes in pregnancy

– Triglycerides

-Albumin & total protein

-GFR

~40% increase

decreased<– hemodilution

increased<– increased BV

Insulin resistance in pregnancy

after mid-2nd trimester –> increased insulin resistance

<– hPL –> anti-insulin effects~GH

Na+ ,K+ & Ca2+ in pregnancy

Na+ & K+ ~ constant

Ca2+ –> falls slightly

 

 SLE flare1 vs. pregnancy induced hypertension2

Test for Dx?

Complement levels

1low , 2normal

Clean catch voided urine specimen

>100,000 col/mL

Pt: asymptomatic female – Dx & Rx & cause

Asymptomatic bacteriuria (E.coli)–> 10-20% of women Pregnancy–> 40% pyeloniphritis => Rx:AB
Most common cause of hypopituitarism in women of chilbearing age

Sheehan syndrome = postpartum pituitary apoplexy

<– severe blood loss @ delivery & pituitary enlargement a/w pregnancy

Most common thyroid disorder in pregnancy

Best test –>thyroid status?

Hypothyroidismin Pt w borderline thyroid function/available iodine Estrogen–> incr.TBG, hCG–>TSH-like stimulatory effect

=>increased demand

Most common cause of hyperthyroidism in pregnancy

DDX?

Syndrome of transient hyperthyroidism of hyperemesis gravidarum <– high levels of hCG ~ TSH-like effect

DDx: true hyperthyroidism

Recurrent Pregnancy loss

Endometrial biopsy: >2d discrepant with dates

Dx?

Luteal phase defect

Recurrent Pregnancy loss

when and what tests?

≥ 2 spontaneous abortions

parental karyoting (+abortus), endometrial bx / cultures (subclinical Ureaplasma/Chlamydia infection)

Thyroid function tests, lupus anticoagulants

Liver bx in pregnant woman: Widespread microvesicular steatosis, accentuated paracentrally (zone 3)

Paucity of inflammatory activity/ hepatocellular necrosis

Dx?

 

Acute fatty liver of pregnancy (rare), usually 3rd trim.

complicated by DIC, 30% fatality rate

Liver bx in pregnancy:

Pericentral (zone 3) region: dilated canaliculi containing bile plugs – Dx

Most characteristic lab finding?

Intrahepatic cholestasis

increased [Bile acids]serum

HbA1c in pregnancy

Alternative test?

hormonal changes cause greater short-term fluctuation in [glucose]

fructosamine : 2-3wks

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