7.3 Rh Phenotyping and Clinical Significance
Key Takeaways
- Modern D reagents are IgM monoclonal or IgM/IgG blends. High-protein reagents need an Rh control; a positive control invalidates the D type.
- Chronically transfused patients, especially with sickle cell disease, should receive C, c, E, e, and K matched red cells when feasible so they do not add Rh and Kell antibodies to the problem list.
- Give D-neg red cells to D-neg women of childbearing potential. Platelets can carry residual red cells — prefer D-neg platelets or give RhIG after D+ platelets.
- Anti-G is separated from anti-C+D by adsorption with r' (dCe) and R0 (Dce) cells. A D-neg pregnant patient who has anti-G but not anti-D still needs RhIG.
- Unexpected anti-D in a D+ patient is partial D (or passive RhIG/IVIG) until proven otherwise. Mixed-field D after transfusion is not a new inherited type.
7.3 Rh Phenotyping and Clinical Significance
Quick Answer: Type D with IgM monoclonal or IgM/IgG blend reagents. High-protein anti-D can false-positive; you need an Rh control. Do not phenotype recently transfused patients and believe it. Chronically transfused patients, especially sickle cell, should get C, c, E, e, and K matched red cells when you can. RhIG indications start here; full dosing lives in the HDFN chapter. D-neg women of childbearing potential get D-neg RBC, and D-neg platelets when possible — platelets carry residual RBC, so give RhIG if a D+ platelet is issued. Exam classics: anti-G versus anti-C+D (adsorption) and unexpected anti-D in a D+ patient = partial D.
Section 7.1 gave you haplotypes. Section 7.2 gave you weak versus partial D. This section is the bench and the blood order. II.B.3 still owns it; transfusion-practice chapters will reuse every rule.
Reagents, controls, and who you must not type
Current D reagents are low-protein monoclonal IgM (immediate-spin direct agglutination) or IgM/IgG blends (IS plus the option to take the same tube to AHG for weak D). IgM clones differ in which partial D they see. That is a feature: patient reagents may miss DVI so the patient is managed as D-neg; donor reagents must detect DVI so the unit is labeled D+. Do not “fix” a DVI patient by switching to a donor clone and relabeling them D+.
High-protein anti-D — older human polyclonal reagents in albumin or other potentiators — can agglutinate DAT-positive cells even when D is absent. Those reagents require an Rh control: the same diluent without anti-D. A positive control invalidates the D type. Repeat with a low-protein monoclonal, wash the cells, check the DAT, and do not report D+ off a sticky high-protein tube. Run a control whenever the sample is DAT-positive, when the patient types AB, D+ with a reagent that needs it, or whenever the SOP says the diluent can cause spontaneous agglutination.
Recently transfused patients circulate donor red cells. A D type, and especially a C/c/E/e phenotype, can be mixed-field or frankly the donor’s type. Do not call a newly mixed-field D a genetic change. Use a pretransfusion type, reticulocyte separation if the SOP allows it, or molecular RH typing on white-cell or buccal DNA (Chapter 5). The same warning applies after HPC transplant: the forward type can migrate toward the donor over weeks.
C, c, E, and e reagents are monoclonal or polyclonal and are read by the manufacturer’s phase. Enzyme-treated cells type stronger for Rh and can help a weak e, but they also enhance cold autoantibodies — do not create an e+ you cannot defend.
D typing discrepancies you will be handed
Work them in this order:
- Clerical and reagent. Wrong sample, expired clone, under-centrifuged tube.
- Mixed field. Recent D+ or D− transfusion, fetomaternal bleed, transplant. History first.
- Weak or discrepant D between two reagents. Partial D or weak D. Do not average the grades. Follow Section 7.2: protect as D-neg, genotype if the patient is a candidate.
- DAT-positive / control-positive. Invalid D with high-protein or AHG reagents. Clean the cells or switch reagents.
- Historical D+ now D−, or the reverse. Look for transplant, massive transfusion, or a prior mis-type on a partial D clone.
Do not report a D type you cannot defend, and do not issue D+ red cells to a woman of childbearing potential while the discrepancy is open.
Who gets phenotype-matched blood
Chronically transfused patients, especially sickle cell disease and to a lesser extent thalassemia, form Rh and Kell antibodies at a rate that wrecks later support. Standard U.S. practice is to issue red cells matched at least for C, c, E, e, and K (and ABO/D, obviously). Many programs add Duffy, Kidd, and S once an antibody appears, or up front if a genotype is already on file. African-ancestry patients are enriched for partial D, partial C, and partial e; a serologic match can still allow alloanti-D or alloanti-e. When the antibody ID looks like anti-e in an e+ sickle-cell patient, think partial e and send RHCE genotyping, do not just call it warm auto and give least-incompatible e+ units forever.
Extended matching is not required for a one-time orthopedic transfusion in a patient with a negative antibody screen. Do not spend C−E−K− units on that case; those units belong to the sickle-cell service.
RhIG preview — indications, not the full dose math
Rh immune globulin prevents anti-D formation in a D-neg person exposed to D+ red cells. Classic obstetric indications, with dosing reserved for the HDFN chapter:
- Antepartum, about 28 weeks, when the mother is D-neg and has not already made immune anti-D.
- Postpartum, within 72 hours, if the infant is D+ or weak D+.
- After miscarriage, abortion, ectopic, amniocentesis, CVS, version, abdominal trauma, or stillbirth when the fetus could be D+.
RhIG is not indicated if the mother already has immune anti-D. It is still indicated if she has anti-C, anti-E, or anti-G without anti-D — those antibodies do not protect her from making anti-D. Antepartum RhIG will make the antibody screen positive; that passive anti-D is not a reason to skip the postpartum dose when the infant is D+. Full vial math, Kleihauer–Betke, and rosette testing belong in the HDFN chapter. Here you only need the trigger list and the anti-G exception.
Women of childbearing potential, red cells, and platelets
A D-neg woman who can still become pregnant receives D-neg red cells unless a massive-bleeding protocol has emptied that inventory and the medical director has accepted the immunization risk. The same woman should receive D-neg platelets when possible. Platelet units are not “red-cell free.” Apheresis and whole-blood platelets contain residual erythrocytes, enough to immunize. If a D+ platelet must be issued, give RhIG. One standard 300 µg vial covers far more red-cell volume than a platelet dose contains; you do not need a Kleihauer after a platelet. D-neg men and D-neg women who are not of childbearing potential may receive D+ platelets without RhIG when inventory demands it — local policy decides, but the exam’s protected person is the woman who can still carry a D+ fetus.
Plasma and cryoprecipitate do not carry a meaningful D-immunization risk. Do not waste RhIG on AB plasma.
Exam scenario: anti-G versus anti-C+D
A D-neg, C-neg patient (usually rr) has a serum that reacts with every C+ or D+ cell and misses rr cells. That pattern is anti-C+D, anti-G, anti-C+G, anti-D+G, or the full trio. You cannot tell from the panel alone.
Adsorption geometry uses the two cells that carry G with only one of the major antigens:
| Adsorbing cell | Antigens | Removes | Leaves behind |
|---|---|---|---|
| r' (dCe) | C+ G+ D− | anti-C and anti-G | anti-D |
| R0 (Dce) | D+ G+ C− | anti-D and anti-G | anti-C |
If r' cells remove all activity, there was no anti-D — the serum was anti-G ± anti-C. If activity remains after r' adsorption and that leftover reacts with D+ C− cells, anti-D is present. Repeat the logic with R0 cells to ask whether anti-C exists. Eluates off each adsorbing cell confirm what bound.
Why the BB exam cares: a prenatal patient with anti-G but not anti-D still needs RhIG and still needs the infant monitored, but the antibody you are titering for D-HDFN risk is not there. Treat her as if she had anti-C+D and you will skip RhIG and mis-counsel. Treat every G pattern as “she already has anti-D” and you make the same mistake.
Exam scenario: unexpected anti-D in a D+ person
A patient types D+ (sometimes weak, sometimes 3+) and the antibody ID is anti-D. Autocontrol may be negative. This is alloanti-D in a partial D until you prove otherwise. Manage as D-neg for red cells, offer RhIG if she is pregnant and the anti-D could still be passive, and send RHD genotyping. Differential to keep honest:
- Passive anti-D from recent RhIG or IVIG — history, low titer, declining.
- Autoanti-D — positive autocontrol / DAT, panagglutinin after warm autoadsorption may remain D-like.
- Anti-LW — can mimic anti-D; DTT-treated or cord-cell patterns differ; rare on BB stems.
Do not “correct” the D type to negative on paper and forget to tell the transfusion service. Do not issue D+ units because the analyzer printed D+.
Exam traps
- Reporting D+ off a positive Rh control.
- Phenotyping a patient who was transfused yesterday and treating the mixed field as genotype.
- Matching only D and K in a sickle-cell program and ignoring C, c, E, e.
- Withholding RhIG because anti-G “already covers D.”
- Giving D+ platelets to a D-neg woman of childbearing potential without RhIG.
- Calling unexpected anti-D in a D+ patient an autoantibody without considering partial D.
A hospital sickle-cell program is writing a prophylactic matching policy for patients who have not yet made an alloantibody. Which red-cell antigens should be matched in addition to ABO and D?
A D-neg, C-neg prenatal patient has serum that reacts with all D+ or C+ panel cells. After adsorption onto r' (dCe) cells, no activity remains toward D+ C− cells. What is the correct interpretation and RhIG decision?
A woman types D+ with a monoclonal blend. The antibody identification is anti-D, the autocontrol is negative, and she has no recent RhIG or IVIG. What is the best explanation?