Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (644 page)

   Considerations

The maternal alloantibodies to red cell antigens that cause HDFN may be produced because of prior exposure to blood due to transfusion or pregnancy. When alloimmunization occurs due to pregnancy, it is usually at the time of delivery or late in the pregnancy. Thus, it is unlikely that HDFN would occur during the first pregnancy if the patient has no history of transfusion of blood products.

Rh PROPHYLAXIS

Prior to the use of RhIg, anti-D was the most common cause of HDFN as the D antigen is very immunogenic. If appropriately used, RhIg can prevent almost all cases of alloimmunization to the D antigen in Rh-negative pregnant patients. However, if the patient has already been immunized to the D antigen and made the anti-D alloantibody, administration of RhIg does not provide any benefit and is not indicated. Generally, a single 300-μg vial of RhIg (which will cover 30 mL of fetal whole blood or 15 mL of fetal red cells) is given prophylactically at 28 weeks if the patient is D negative. A subsequent dose is then administered shortly after (but must be within 72 hours of) delivery if the neonate is D positive. The amount of RhIg to be given after delivery is determined by testing the mother’s blood for the presence of fetal red cells. Often the initial screening test for maternal–fetal hemorrhage is the rosette test, which is performed by adding anti-D to maternal blood, followed by indicator D-positive red cells. This results in “rosettes” or agglutination of red cells surrounding the D-positive fetal red cells. The rosette test will be positive if the volume of fetal blood in maternal circulation is >30 mL. If the rosette test is negative, one vial of RhIg is administered to cover the small amount of fetal blood in the maternal circulation that may be present. If the rosette test is positive, the amount of fetal red cells in the maternal circulation can be quantitated using flow cytometry or the Kleihauer-Betke (acid/elution) test. The Kleihauer-Betke is performed by treating maternal red cells on a thin slide smear with acid and then counterstaining the slide. Fetal hemoglobin is resistant to acid treatment so maternal cells will appear as “ghosts” while fetal cells will be pink. Usually, 2,000 cells are counted, and the percentage of fetal red cells is determined and multiplied by the maternal blood volume to determine the volume of fetal blood in the maternal circulation. The maternal blood volume can be calculated using the mother’s height and weight or alternatively 5,000 mL is occasionally used as an estimate of the blood volume of postpartum women. Alternatively, flow cytometry can also be used to determine the amount of fetal–maternal hemorrhage. The amount of RhIg to be given to the mother is then determined using the estimated volume of fetal blood in circulation that must be covered by RhIg. The volume of fetal–maternal hemorrhage is then divided by 30 mL (that each 300 μg vial of RhIg will cover) to determine the number of vials necessary. The result of the calculation is rounded to the closest whole number and then one additional vial is added to allow for an error in the estimation/calculation. Additional doses of RhIg may also be necessary in Rh-negative women if the patient has any events that may have introduced fetal blood into the maternal circulation such as trauma, version, abortion, or amniocentesis (please refer to the suggested reading for additional discussion).

CONCLUSION

Over the last 100 years, there have been significant advances in the field of transfusion medicine. All of the major blood groups have been identified and techniques for serologic testing have been developed. Today, almost all hospitals have blood banks that are able to provide blood products to patients who require them. Although transfusion can be life saving, there are significant risks associated with blood product transfusion. Thus, blood products should only be transfused if necessary.

Suggested Readings

Roback J, Grossman B, Harris T, et al., eds.
Technical Manual
, 17th ed. Bethesda, MD: AABB Press; 2011.

Simon T, Snyder E, Solheim B, et al., eds.
Rossi’s Principles of Transfusion Medicine
, 4th ed. Bethesda, MD: Blackwell Publishing; 2009.

SECTION
12

LAB TESTS

Chapter
16

Laboratory Tests

Lokinendi V. Rao and Liberto Pechet

1,5-Anhydroglucitol (1,5-AG)

11-Deoxycortisol

17α-Hydroxyprogesterone

17-Ketosteroids, Urine (17-KS)

5,10-Methylenetetrahydrofolate Reductase (MTHFR) Molecular Assay

5-Hydroxyindoleacetic Acid (5-HIAA) Urine

5′-Nucleotidase (5′-ribonucleotidephosphohydrolase, 5′-NT)

Acetaminophen (
N
-Acetyl-
p
- Aminophenol; APAP)

Acetylsalicylic Acid

Acid Phosphatase

ACTH Stimulation (Cosyntropin) Test

Activated Clotting Time (ACT)

Activated Protein C Resistance (APCR)

Adiponectin

Adrenocorticotropic Hormone (ACTH)

Allergen Tests, Specific Immunoglobulin E (IgE)

Albumin, Serum

Alcohols (Volatiles, Solvents)

Aldosterone

Alkaline Phosphatase (ALP)

Alpha
1
-Antitrypsin (AAT, Alpha-1 Trypsin Inhibitor, Alpha-1 Proteinase Inhibitor)

α-Fetoprotein (AFP) Tumor Marker, Serum

Aminotransferases (AST, ALT)

Ammonia (Blood NH
3
, NH
₃
, NH
₄
)

Amniocentesis

Amphetamines

Amylase

Amylase, Urine (Amylase/Creatinine Clearance Ratio [ALCR])

Androstenedione, Serum

Angiotensin II

Angiotensin-Converting Enzyme (ACE, Kinase II)

Anion Gap (AG)

Antiarrhythmic Drugs

Antibiotics

Anticardiolipin Antibodies (ACAs)

Anticoagulants, Circulating

Anticoagulation DNA Panel

Anticonvulsants

Antidepressants

Antidiuretic Hormone

Antihypertensives

Anti-inflammatories

Antineoplastics

Antimitochondrial Antibodies

Anti–Smooth Muscle Antibodies (ASM)

Anti-parietal Cell Antibodies (APC)

Antineutrophil Cytoplasmic Antibody (ANCA)

Antinuclear Antibody (ANA)

Antipsychotics

AntiSperm Autoantibodies– Immunobead Binding Test

Antithrombin (AT)

Apolipoproteins (Apo) A-1 and B

Benzodiazepines

Beta-2 Microglobulin, Serum, Urine, Cerebrospinal Fluid

Bicarbonate (HCO
3−
), Blood

Bilirubin; Total, Direct, and Indirect

Bleeding Time (BT)

Blood Gas, pH

Blood Urea Nitrogen (BUN)

Bone Marrow Analysis

Brain Natriuretic Peptide (BNP)

Bronchodilators

β-Trace Protein

BUN-to-Creatinine Ratio

Calcitonin

Calcium, Ionized

Calcium, Total

Calcium, Urine

Calprotectin, Stool

Cancer Antigen 15-3 (CA 15-3)

Cancer Antigen 19-9 (CA 19-9)

Cancer Antigen 27.29 (CA 27.29)

Cancer Antigen-125 (CA-125), Serum

Cannabis Sativa

Carbon Dioxide, Total

Carboxyhemoglobin (Carbon Monoxide, COHB, HBCO)

Carcinoembryonic Antigen (CEA)

Cardiovascular Drugs (See Digoxin)

Catecholamines, Serum

Cell Count, Body Fluid Analysis

Cerebrospinal Fluid (CSF)

Other Body Fluids: Pleural, Pericardial, and Peritoneal Spaces

Ceruloplasmin

Chloride

Chloride, Urine

Cholesterol, High-Density Lipoprotein (HDL)

Cholesterol, Low-Density Lipoprotein (LDL)

Cholesterol, Total, Serum

Cholinesterase (Pseudocholinesterase) and Dibucaine Inhibition

Chorionic Villus Sampling

Chromogranin A, Plasma

Clot Retraction

Clotting Factors

Clotting Time (Lee-White Clotting Time)

Cobalt

Cocaine

Cold Agglutinins

Combined First-Trimester and Second- Trimester Screening (Integrated/ Sequential Screening)