Master the board step 3

Master the Boards: USMLE Step 3
Screening Test Diagnostic Significance Next Step in Management
FIRST TRIMESTER ROUTINE TESTS
Anemia,
blood
disorders
Blood type, Rh,
and antibody
Genitourinary
screening
Immunization
status
Infection:
Syphilis
CBC
Type and screen
Direct and
indirect
Coombs
Cervical PAP
smear
Urinalysis/
Urine culture
Rubella antibody
Hepatitis B
surface
antigen
• Anemia = Hb < 10 g/dL (normal:
10–12 g/dL). The most reliable
indicator of true anemia is MCV.
• Most common cause of anemia is
iron deficiency.
• WBC > 16,000/mm 3 is abnormal.
• In pregnancy, caused by ↑ levels
of hepcidin, which inhibits iron
transport. Pregnancy ↑ iron
demand, but hepcidin prevents
absorption.
• Rh negative mothers may
become sensitized (anti-D Ab) →
risk of erythroblastosis fetalis in
the next pregnancy.
• Indirect Coombs test (or atypical
antibody test [AAT]) detects
atypical RBC Ab’s.
• Detects cervical dysplasia or
malignancy.
• UA: Screen for underlying renal
disease and infection.
• UCx: Screen for asymptomatic
bacteriuria (ASB).
• (−) Rubella IgG Ab’s means ↑ risk
of primary rubella infection.
• (+) HBsAg: Indicates risk for
vertical transmission of HBV
VDRL or RPR Confirm (+) VDRL/RPR with
treponema-specific tests (MHATP
or FTA).
PO = oral; IM = intramuscular; Ab’s = antibodies; Hb = hemoglobin
• ↓ hemoglobin ↓ MCV: Give
iron. Test for thalassemia if
anemia does not improve.
• ↓ hemoglobin ↑ MCV
↑RDW: Give folate.
• Thrombocytopenia
(< 150,000/ mm 3 ): Correlate
clinically for ITP or HELLP
syndrome.
• Give RhoGAM to Rh negative
mothers at 28 weeks after first
rescreening for absence of anti-D
antibodies.
• Give RhoGAM in Rh negative
mothers after any procedure
(CVS, amniocentesis) and after
delivery.
• See Gynecology section for
management.
• Always treat ASB in pregnancy to
prevent pyelonephritis (30% risk
when untreated).
• Rx: Nitrofurantoin (before
30 weeks), cephalosporins,
amoxicillin
• Do not give Rubella immunization
in pregnancy.
• Immunize seronegative patients
after delivery.
• (+) HBsAg: Order HBVe antigen.
• (+) HBeAg signifies a highly
infectious state.
• (+) confirmatory test: Treat with
intramuscular penicillin.
• Penicillin allergic: Desensitize and
then treat with penicillin.
(continued next page)
418