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Rh immune globulin and fetomaternal hemorrhage

16 min

Skills you'll build3 skills
  • Determine postpartum Rh immune globulin eligibility from the laboratory results
  • Calculate fetomaternal hemorrhage volume from a Kleihauer-Betke count
  • Calculate the RhIG dose in whole syringes from the hemorrhage volume and product label

Try first

Try first

A D-negative patient received Rh immune globulin at 28 weeks, after a negative antibody screen drawn before the dose. At delivery at 39 weeks her screen shows a weak anti-D, and her baby is D-positive. What does the laboratory report about postpartum Rh immune globulin?

Keep going to see the reasoning.

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

Rh immune globulin candidates

Rh immune globulin supplies passive anti-D. It prevents a D-negative mother from forming her own anti-D. After delivery the laboratory answers three questions in order:1,2

  1. Is the mother at risk? A weak D type 1, 2 or 3 is managed as D-positive, and she needs no prophylaxis. An unresolved D variant is managed as at risk.
  2. Is her anti-D immune? Confirmed immune anti-D makes prophylaxis ineffective. Anti-D after an antenatal dose is often passive and can stay detectable for months. With passive or uncertain anti-D, she remains a candidate.
  3. Is the infant D-positive? A D-negative first result is followed by a weak D test. Only a negative result on both tests classifies the infant as D-negative. A blocked-D or indeterminate result is managed as D-positive.

Passive and immune anti-D are distinguished by the pre-dose screen and the dose history. Reaction strength and titer cannot separate them.3 The postpartum target is administration as soon as possible and within 72 hours.1,4

Measuring the bleed

A rosette screen detects D-positive fetal cells in a D-negative mother. A maternal D variant or a weakly expressed infant D makes it unsuitable, and a quantitative method is used from the start. A valid negative screen supports one standard dose.1

The Kleihauer-Betke test treats a maternal blood film with acid and then counterstains it. Fetal cells contain acid-resistant hemoglobin F and stay stained. Adult cells lose their hemoglobin and appear as pale ghosts. Maternal F cells raise the estimate falsely, and flow cytometry measures more precisely where it is available.1

A flow method's marker must fit the maternal and infant D results. HbF-based methods detect fetal cells independently of D expression and must account for maternal F cells. Anti-D methods avoid maternal F-cell interference in a D-negative mother. They require a reagent that detects the infant's D variant and a second marker that excludes autofluorescent neutrophils.6,7

Estimated fetal whole blood (mL) = percentage of fetal cells among the cells counted × 50, with the percentage entered as a number (2.6 for 2.6%). The factor 50 assumes a maternal blood volume of 5,000 mL, and maternal F cells or counting error can change the estimate.5

Calculating the dose

RhoGAM 300 µg (1,500 IU) syringes = D-positive red cells (mL) ÷ 15, or D-positive whole blood (mL) ÷ 30, before rounding. The label doses 20 µg per mL of red cells (20 × 15 = 300 µg), and the 30 mL whole-blood figure is the conventional equivalent of 15 mL of red cells.1,2 The fetal-cell count is imprecise, so the AABB calculation adds a margin:5

  1. Round the result to the nearest whole syringe. A fraction of .5 or more rounds up.
  2. Add one syringe.

The report states the estimated hemorrhage, the coverage of the product supplied and the number of whole syringes. The clinical service orders and gives the dose.2

Follow the bench demonstration

Sources for this step
References
  1. AABB. Association Bulletin #24-02: Use of Rh Immune Globulin and Considerations in the Setting of Supply Shortages and Limited Availability. July 15, 2024. Accessed September 27, 2026.
  2. Kedrion Biopharma Inc. RhoGAM Ultra-Filtered PLUS and MICRhoGAM Ultra-Filtered PLUS [prescribing information]. Revised July 2025. Accessed September 27, 2026.
  3. Regan F, Veale K, Robinson F, et al. Guideline for the investigation and management of red cell antibodies in pregnancy: a British Society for Haematology guideline. Transfus Med. 2025;35(1):3-23. doi:10.1111/tme.13098
  4. American College of Obstetricians and Gynecologists. Practice Bulletin No. 181: prevention of Rh D alloimmunization. Obstet Gynecol. 2017;130(2):e57-e70. Reaffirmed 2026. doi:10.1097/AOG.0000000000002232
  5. Bloch EM, Campbell-Lee S, McKenna DH Jr, Montemayor-Garcia C, Schwartz J, Shaz B, Storry J, eds. Technical Manual. 22nd ed. AABB; 2026.
  6. Porter L, Hazell M, Eggington J, et al. BSH guideline for the estimation of fetomaternal haemorrhage. Transfus Med. Published online June 12, 2026. doi:10.1111/tme.70076
  7. Mayo Clinic Laboratories. Fetomaternal Bleed, Flow Cytometry, Blood. Accessed October 27, 2026.

Watch one

Read each decision and its explanation.

A D-negative mother with a negative pre-delivery antibody screen and no anti-D has delivered a D-positive baby. Her rosette screen is positive. A Kleihauer-Betke test counts 45 fetal cells among 2,000 cells. The product supplied is a 300 µg (1,500 IU) syringe.

How many syringes does the laboratory report?

  1. Confirm the pathway. She is D-negative with no anti-D, the baby is D-positive, and the positive rosette screen requires a Kleihauer-Betke test.

    A dose is calculated only for a candidate, and a positive screen requires quantitation.

  2. Fetal cells: 45 ÷ 2,000 × 100 = 2.25%.

    The count gives fetal cells as a share of all cells counted.

  3. Fetal whole blood: 2.25 × 50 = 112.5 mL.

    The factor 50 represents a maternal blood volume of 5,000 mL.

  4. Syringes before rounding: 112.5 mL ÷ 30 mL = 3.75.

    One syringe covers 30 mL of fetal whole blood, the same as 15 mL of fetal red cells.

  5. Round 3.75 up to 4, then add one: 5 syringes.

    The AABB calculation rounds to the nearest whole syringe and adds one for the imprecision of the count.

  6. Report the estimated hemorrhage of 112.5 mL, the coverage of 30 mL of whole blood per syringe and 5 syringes.

    The clinical service orders and gives the dose from the product's label.

5 syringes of 300 µg. 45 ÷ 2,000 = 2.25%. 2.25 × 50 = 112.5 mL of fetal whole blood. 112.5 ÷ 30 = 3.75, rounded to 4, plus one syringe makes 5.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

An eligible D-negative mother has delivered a D-positive baby, and her rosette screen is positive. On her Kleihauer-Betke film, many cells stain at a density between the dark fetal cells and the pale ghosts. A hemoglobin study before this pregnancy found a raised hemoglobin F. Which test gives a count you can use for the dose?

Both readers see the same intermediate cells. Averaging two counts cannot separate maternal F cells from fetal cells.

Anti-D labels the baby's D-positive cells, and her F cells carry no D. The second marker excludes autofluorescent neutrophils from the count.

Her F cells contain hemoglobin F too, so this method must distinguish them from fetal cells. Anti-D counts only the baby's D-positive cells.

A rosette screen detects fetal D-positive cells and gives no count. Her screen is already positive, so the bleed needs a count.

Hint
  1. Ask what the intermediate cells contain.
  2. Look for a marker the baby's cells carry and the mother's cells lack.

Review Quantifying large hemorrhages

Problem 2 of 3 · Hints available

A patient's D typing is weakly reactive at the antiglobulin phase, and RHD genotyping reports weak D type 1. She has just delivered a D-positive baby. What does the laboratory report about Rh immune globulin?

People with weak D type 1 are not at risk of forming anti-D, so prophylaxis is not indicated. The genotype report and the laboratory's D-variant policy support the decision.

The genotype resolves the serologic weak D. People with weak D type 1 are managed as D-positive.

A rosette screen measures a fetal bleed in a D-negative mother. A maternal D variant makes it unreliable, and it does not determine eligibility for Rh immune globulin.

The genotype is already reported, and it determines eligibility for this delivery.

Hint
  1. Rh immune globulin prevents anti-D in a person who could form it.
  2. Find what the genotype report says about her risk of forming anti-D.

Review Laboratory eligibility and dose support

Problem 3 of 3 · On your own

An eligible D-negative mother has a raised hemoglobin F, so her fetal bleed is counted by flow cytometry with a validated anti-D method. It reports 3.9% fetal cells. Each syringe is 300 µg (1,500 IU). How many syringes does the laboratory report?

Show the answer

8 syringes

3.9 × 50 = 195 mL of fetal whole blood. 195 ÷ 30 = 6.5, rounded up to 7, plus one syringe makes 8.

Review Quantifying large hemorrhages

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • Maribel Tubbs, 33, MRN 5620194, delivered a baby girl 2 hours ago.
  • She is D-negative, her antibody screen before delivery was negative, and she received no Rh immune globulin in this pregnancy.
  • The baby's red cells are D-negative at immediate spin. The weak D test at the antiglobulin phase is 2+, with a nonreactive control.
  • The product on hand is a 300 µg (1,500 IU) syringe.
Decision 1 of 3

Is the mother a candidate for postpartum Rh immune globulin?

The weak D test is part of the infant's D typing. A 2+ weak D result with a valid control makes the baby D-positive.

The mother is D-negative with no anti-D, and the baby's D is weakly expressed. She is a candidate, and the fetal bleed is measured next.

The weak D result is valid today. Waiting a day uses up time toward the 72-hour target.

Review Laboratory eligibility and dose support

Decision 2 of 3

Which test measures the fetal bleed?

The rosette screen can miss weakly expressed fetal D. This baby's D reacted only in the weak D test, so the screen is unsuitable.

She has no anti-D. A maternal anti-D titer does not measure a fetal bleed.

Both detect fetal hemoglobin independently of D expression. Anti-D flow can miss a weak D population.

One standard dose is given only after a valid negative screen. A larger bleed needs more.

Review Quantifying large hemorrhages

Decision 3 of 3

The Kleihauer-Betke test counts 26 fetal cells among 2,000 cells. How many syringes does the laboratory report?

The calculation gives 2.17, which rounds to 2. One more syringe covers the imprecision of the count.

Did not add the extra syringe

The AABB calculation rounds to the nearest whole syringe and then adds one, because the fetal-cell count is imprecise. A calculation of 3.75 becomes 4 + 1 = 5. Stopping at 4 can leave part of the hemorrhage uncovered, and the patient can still form anti-D.

The 65 mL estimate is fetal whole blood. Dividing it by the 15 mL red-cell coverage nearly doubles the dose.

Confused fetal red-cell volume with fetal whole-blood volume

Percent fetal cells × 50 gives the fetal whole-blood volume in mL, and the fetal red-cell volume is about half of that. Dividing a whole-blood estimate by the 15 mL red-cell coverage doubles the dose, and dividing a red-cell estimate by the 30 mL whole-blood coverage halves it and leaves part of the hemorrhage uncovered.

One standard dose covers 30 mL of fetal whole blood. This bleed is 65 mL.

26 ÷ 2,000 × 100 = 1.3%. 1.3 × 50 = 65 mL of fetal whole blood. 65 ÷ 30 = 2.17, rounded to 2, plus one syringe makes 3.

Review Quantifying large hemorrhages

The baby's positive weak D test made the mother a candidate and made the rosette screen unsuitable. The dose of 3 syringes was calculated from the Kleihauer-Betke count.

For reference

Sources checked