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The test is used in several settings: 1. In Rh– mothers to determine if they have been exposed to Rh+ fetal blood. If they have, it is used to determine the dose of Rh immune globulin needed by the exposed mother to prevent future episodes of hydrops fetalis; 2. in pregnant women who have experienced traumatic injury, it is used to identify the presence of fetomaternal hemorrhage; 3. in amniocentesis, to determine whether any blood found to be present is maternal or fetal in origin. A sample of maternal blood is obtained from a vein and treated with acid. Maternal blood cells develop a pale, ghostly appearance when exposed to acid; fetal cells do not. The number of fetal cells identified microscopically per a specified number of low-power fields is used to estimate the mL of fetal bleeding into the maternal circulation.
SpecimenWhole blood (1 mL) collected in a lavender-top (EDTA) tube. Freshly prepared blood smears are also acceptable. Cord blood may be requested for use as a positive control.
This procedure is contraindicated for
- Assist in the diagnosis of certain types of anemia
- Calculating dosage of RhoGAM
- Determine whether FMH was a potential cause of death in stillborn delivery
- Screening postpartum maternal blood for the presence of FMH
Positive findings in:
- Fetal-maternal hemorrhage (related to leakage of fetal RBCs into maternal circulation)
- Hereditary persistence of fetal hemoglobin (the test does not differentiate fetal hemoglobin from neonate and adult)
Specimens must be obtained before transfusion.
Nursing Implications and Procedure
- Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
- Patient Teaching: Inform the patient this test can assist in identifying how much medication should be given after delivery.
- Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
- Obtain a history of the patient’s hematopoietic and reproductive systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
- Note any recent procedures that can interfere with test results.
- Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
- Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
- Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
- Note that there are no food, fluid, or medication restrictions unless by medical direction.
- Potential complications: N/A
- Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
- Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
- Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
- Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
- Promptly transport the specimen to the laboratory for processing and analysis. Sample must be less than 6 hr old.
- Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
- Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
- Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
- Related tests include amniotic fluid analysis, blood group and type, hemoglobin electrophoresis, and US biophysical profile obstetric.
- Refer to the Hematopoietic and Reproductive systems tables at the end of the book for related tests by body system.