RhIG to an Rh positive Patient? The Medical Splenectomy

Why Would an Rh-Positive Male Patient Receive RhIG?

The nursing floor just requested Rh immune globulin for an RhD-positive male patient.

Wait...what?

He obviously isn't getting RhIG to prevent RhD alloimmunization.

One possible explanation is immune thrombocytopenia (ITP).

What Is ITP?

Immune thrombocytopenia (ITP) is an autoimmune disorder in which the immune system targets the patient's own platelets, resulting in accelerated platelet clearance and, in some patients, impaired platelet production.

The spleen plays an important role in this process. Antibody-coated platelets are recognized by macrophages through Fc receptors and removed from circulation, producing thrombocytopenia.

Treatment depends on the platelet count, bleeding, clinical circumstances, and whether the disease is newly diagnosed, persistent, or chronic.

Corticosteroids remain an important initial treatment in adults who require therapy. IVIG can also be used when a rapid increase in platelet count is needed or in selected clinical situations. Current treatment options for persistent or chronic disease also include thrombopoietin-receptor agonists, rituximab, and splenectomy. (hematology.org)

But there is another, somewhat unusual way to temporarily increase the platelet count:

IV Anti-D Immune Globulin

Certain Rh(D) immune globulin products can be administered intravenously to RhD-positive patients with ITP.

Yes—the same basic antibody specificity we normally associate with preventing RhD alloimmunization can be deliberately given to a person whose own red cells express the D antigen.

For ITP treatment, FDA-approved examples include WinRho SDF and Rhophylac. This use is restricted to appropriate RhD-positive, nonsplenectomized patients, although the exact approved patient populations differ between the products.

This is sometimes informally referred to as a “medical splenectomy.”

No spleen is actually being removed, of course. Instead, the goal is to temporarily redirect splenic macrophage activity away from antibody-coated platelets.

How Does It Work?

The anti-D in IV RhIG binds to the patient's RhD-positive red blood cells, coating them with IgG.

Those antibody-coated RBCs are then recognized by macrophages of the reticuloendothelial system, particularly in the spleen.

The exact mechanism is not completely understood, but the traditional model is that clearance of the anti-D-coated RBCs occupies or alters Fc-receptor-mediated macrophage activity. The antibody-coated RBCs are preferentially removed while antibody-coated platelets are temporarily spared.

The end result can be a rise in the circulating platelet count.

WinRho's prescribing information specifically describes this as preferential removal of anti-D-coated RBC complexes by the reticuloendothelial system, resulting in Fc-receptor blockade and sparing of antibody-coated platelets.

There's a Catch: Hemolysis

If you're intentionally coating someone's RBCs with anti-D and sending them toward the spleen, there is an obvious consequence:

You're going to lose some red cells.

A fall in hemoglobin after IV anti-D therapy is expected. In pooled WinRho clinical studies, the average hemoglobin decrease was approximately 1.2 g/dL within seven days of treatment.

This is why the patient's hemoglobin and evidence of hemolysis matter before and after treatment.

But hemolysis isn't always mild.

Both WinRho and Rhophylac carry a boxed warning for intravascular hemolysis when used to treat ITP. Severe reactions have resulted in clinically significant anemia, acute kidney injury or renal failure, disseminated intravascular coagulation, multiorgan failure, and death. Patients receiving IV anti-D for ITP therefore require close monitoring after administration.

WinRho specifically should not be used in patients with autoimmune hemolytic anemia, pre-existing hemolysis, or a high risk for hemolysis. Its labeling also recommends alternative treatment when the hemoglobin is below 8 g/dL and dose reduction when it is below 10 g/dL.

Why Does the Patient Need a Spleen?

The mechanism depends heavily on splenic clearance of anti-D-coated RBCs.

If the patient has already undergone splenectomy, this strategy doesn't work reliably enough to justify its use. Accordingly, the FDA-approved ITP indications for both WinRho and Rhophylac specify nonsplenectomized patients.

And obviously, an RhD-negative patient doesn't have enough D antigen on their RBCs for the anti-D to produce the intended effect.

So the seemingly backward requirement makes sense:

For RhIG to treat ITP, you actually want the patient to be RhD-positive.

What If the Patient Needs an RBC Transfusion?

Here's another blood-bank consideration.

If an ITP patient develops significant anemia after receiving IV anti-D and requires RBC transfusion, the WinRho prescribing information recommends RhD-negative RBCs so that additional D-positive cells aren't introduced into an environment containing a large amount of circulating anti-D and ongoing hemolysis.

That can produce the unusual-looking situation where an RhD-positive patient is deliberately being transfused RhD-negative RBCs.

Is IV Anti-D Still Commonly Used for ITP?

It exists, and it remains an FDA-approved treatment, but it occupies a much smaller place in modern ITP management than it once did.

ASH guidelines favor corticosteroids as initial treatment for adults who require therapy. In children with newly diagnosed ITP and no or minor bleeding, observation is preferred; when treatment is needed for non-life-threatening mucosal bleeding, corticosteroids are generally preferred, while IVIG or anti-D can be alternatives in selected circumstances.

The potential for serious hemolysis is an important limitation of IV anti-D therapy, and modern ITP treatment now includes several additional options that weren't available when anti-D first entered widespread use.

Still, if an RhD-positive male patient with a spleen suddenly has an order for IV RhIG, the order may not be a mistake.

Someone may be treating his ITP.

And somewhere in the blood bank, a technologist is staring at the order thinking:

"You want me to give WHAT to WHO?"

Why Would the ER Order FFP for a Patient With a Swollen Tongue?

You get a call from the Emergency Department:

“We need plasma now. The patient's tongue and face are swelling and we're worried about the airway.”

The patient has no blood type on file.

You may be thinking: Why the hell are we giving plasma? They aren't bleeding. Their INR isn't elevated. They're not in massive transfusion.

Depending on your institution's emergency plasma policy, you may end up thawing group AB plasma or another plasma product approved by your facility for emergency use before the patient's ABO type is known.

So what exactly is happening?

One possibility is ACE inhibitor-induced angioedema.

And in severe cases, fresh frozen plasma has historically been used as an unusual rescue treatment.

ACE Inhibitors and Angioedema

Angiotensin-converting enzyme inhibitors—such as lisinopril, enalapril, ramipril, and others—are widely used to treat hypertension, heart failure, and other cardiovascular conditions.

One uncommon but potentially life-threatening adverse effect is angioedema, particularly involving the lips, tongue, face, pharynx, and larynx.

Importantly, this is usually not an allergic, histamine-mediated reaction.

It is primarily a bradykinin-mediated reaction.

ACE inhibitor-associated angioedema can occur at essentially any point during therapy; FDA labeling for ACE inhibitors specifically warns that angioedema may develop at any time during treatment.

What Does ACE Normally Do?

Angiotensin-converting enzyme has more than one job.

Most people learn ACE as the enzyme that converts:

Angiotensin I → Angiotensin II

That explains why inhibiting ACE lowers blood pressure.

But ACE is also known as kininase II, because it helps degrade bradykinin.

Bradykinin is not an enzyme. It is a small vasoactive peptide.

Among other effects, bradykinin causes:

vasodilation
increased vascular permeability
movement of fluid from the intravascular space into surrounding tissues

Normally, ACE helps break bradykinin down.

Give someone an ACE inhibitor and that degradation pathway becomes less effective. In susceptible individuals, excessive bradykinin activity can develop and produce profound localized tissue edema.

Why Does the Tongue Swell?

Bradykinin increases vascular permeability.

Fluid moves from the vasculature into the interstitial tissues, producing the characteristic nonpitting swelling of angioedema.

When that swelling involves an arm or a lip, it may be uncomfortable.

When it involves the tongue, floor of the mouth, hypopharynx, or larynx, it can become a completely different problem.

The airway can progressively narrow until the patient can no longer ventilate adequately.

Patients with anterior tongue swelling, voice changes, drooling, respiratory distress, or deeper airway involvement are at greater risk of needing airway intervention. ACE inhibitor-associated upper-airway angioedema can therefore become a true airway emergency.

And once the airway is badly distorted by edema, intubation may become considerably more difficult.

That means the most important treatment in severe ACE inhibitor angioedema is not a bag of plasma.

It is recognizing a threatened airway early and securing it when necessary.

Why Don't Benadryl, Steroids, and Epinephrine Fix It?

This is where ACE inhibitor angioedema differs from classic allergic angioedema.

In anaphylaxis or other mast-cell-mediated reactions, histamine is an important driver. Epinephrine, antihistamines, and corticosteroids therefore make physiologic sense.

ACE inhibitor angioedema is different.

The principal mediator is bradykinin, not histamine.

As a result, antihistamines and corticosteroids generally do not directly reverse the underlying mechanism, and epinephrine may also have limited effect on the edema itself.

A published case series of patients with progressive ACE inhibitor angioedema described patients who continued to worsen despite epinephrine, antihistamines, and corticosteroids before receiving FFP.

Those medications may still be given initially when the cause of angioedema is uncertain—because anaphylaxis is obviously something you do not want to miss—but lack of response can be another clue that the process is bradykinin-mediated.

And IVIG is not a standard treatment for ACE inhibitor angioedema, so I would remove that from the old version entirely.

So Why Would FFP Help?

Now we finally get back to the blood bank.

Fresh frozen plasma contains a huge collection of normal human plasma proteins and enzymes.

Among them is angiotensin-converting enzyme—kininase II.

Remember what the patient's ACE inhibitor has done:

ACE activity ↓ → bradykinin degradation ↓ → bradykinin activity ↑ → vascular permeability ↑ → angioedema

The proposed reasoning behind FFP is therefore surprisingly straightforward.

By transfusing donor plasma, you introduce functional ACE and other plasma enzymes capable of metabolizing bradykinin.

That may temporarily restore enough bradykinin-degrading capacity to reduce the excessive bradykinin activity and allow the edema to begin resolving.

There are published reports of striking improvement after FFP administration. A seven-patient case series described progressive ACE inhibitor-associated angioedema that improved in temporal association with FFP after conventional treatments had failed. Earlier reports likewise described improvement in otherwise resistant, life-threatening ACE inhibitor angioedema and proposed replacement of kininase II as the mechanism.

That's why you may occasionally receive the bizarre-sounding request:

“I need plasma for angioedema.”

They aren't trying to replace coagulation factors.

They're essentially trying to replace bradykinin-degrading activity.

Does FFP Definitely Work?

Here's where things get less satisfying.

No.

The evidence for FFP in ACE inhibitor angioedema is largely composed of case reports and case series rather than large randomized controlled trials.

That creates a major problem when interpreting reports of rapid improvement: ACE inhibitor angioedema often eventually resolves on its own, so improvement shortly after plasma administration does not necessarily prove that the plasma caused the improvement.

The seven-patient series, for example, showed a temporal association between FFP and improvement—but it was not a randomized trial with an untreated control group.

FFP is also not uniformly effective. Differences in ACE activity between donor plasma units have even been proposed as one possible explanation for variable responses.

And there is an additional wrinkle:

Plasma doesn't contain only enzymes that destroy bradykinin.

It also contains components of the kallikrein-kinin system from which bradykinin can be generated.

Rare cases of worsening angioedema after FFP have therefore been reported.

So FFP should not be thought of as the transfusion-medicine equivalent of naloxone:

Give plasma → bradykinin disappears → problem solved.

The biology is considerably messier than that.

What About Icatibant and Other Bradykinin-Targeted Drugs?

Several medications developed for hereditary angioedema target the same pathway and have therefore been investigated for ACE inhibitor angioedema.

Icatibant, for example, blocks the bradykinin B2 receptor.

An early randomized trial suggested faster resolution with icatibant, but a subsequent larger multicenter randomized controlled trial involving 121 patients found no improvement over placebo in time to discharge or symptom relief.

C1 esterase inhibitor concentrates, kallikrein inhibitors, and other approaches have also been studied or used off-label, but the evidence for ACE inhibitor-associated angioedema has been considerably less definitive than it is for hereditary angioedema.

The FDA-approved indications for drugs such as icatibant and ecallantide are for hereditary angioedema, not ACE inhibitor-induced angioedema.

That is one reason FFP can still occasionally appear in emergency treatment protocols despite the limited evidence: it is widely available in hospitals and has a plausible mechanism of action.

Plasma Isn't Harmless Either

It's also important not to treat FFP like a benign drug simply because the blood bank has a freezer full of it.

Plasma transfusion carries the same important risks it carries in any other setting, including:

allergic and anaphylactic reactions
transfusion-associated circulatory overload (TACO)
transfusion-related acute lung injury (TRALI)
ABO-related hemolysis if incompatible plasma is transfused
citrate-related complications
infectious risk, although modern donor screening and testing make transmission uncommon

FDA plasma labeling continues to list these transfusion-associated risks.

That matters particularly in a patient whose respiratory status may already be precarious.

What Blood Type of Plasma Do You Give?

Historically, the obvious emergency choice for a patient whose ABO type is unknown was group AB plasma, because AB plasma contains neither anti-A nor anti-B.

So the original scenario of thawing AB FFP is perfectly plausible.

However, modern emergency plasma practice is somewhat more flexible.

Some institutions use appropriately selected group A plasma with low-titer anti-B when the recipient's ABO type is not yet known, particularly because group AB plasma is relatively scarce. Current FDA-approved emergency plasma products even include both AB and low-titer group A options for use before the patient's ABO type has been determined.

Exactly what your blood bank issues will depend on its validated emergency plasma policy.

The Blood Bank Perspective

ACE inhibitor angioedema is one of those conditions that can generate a blood-product request that initially makes absolutely no sense.

The patient isn't hemorrhaging.

They don't necessarily have a coagulopathy.

They don't need factor replacement.

They're receiving plasma because something in the plasma itself may function as a drug.

Donor plasma contains functional ACE and other components of the bradykinin metabolism system. By restoring some bradykinin-degrading activity, FFP may help terminate severe ACE inhibitor-associated angioedema in selected patients.

But the important qualifiers are:

FFP is an off-label rescue therapy.

The clinical evidence is limited.

Response is not guaranteed.

Plasma itself carries meaningful transfusion risks.

And most importantly:

If the tongue and upper airway are rapidly swelling, plasma is not a substitute for airway management.

The weird unit of AB plasma you're rapidly thawing in the blood bank may help.

But the anesthesiologist standing beside the patient with an airway cart may be considerably more important.

Why Would an RhD-Positive Baby Type as RhD-Negative?

An intrauterine transfusion can certainly complicate neonatal blood typing, particularly when donor red cells make up a substantial portion of the circulating RBC population. But there is also a rare immunohematologic explanation for an apparently D-negative newborn:

The Blocked D Phenomenon

The blocked D phenomenon can occur in a D-positive fetus or newborn affected by maternal anti-D. Maternal IgG anti-D crosses the placenta and binds to D antigen on the fetal red blood cells. When enough D antigen sites are occupied, the bound maternal antibody can interfere with the ability of routine anti-D typing reagents to react with the cells.

The result can be a false-negative or unexpectedly weak RhD type, even though the infant is genetically D-positive. This phenomenon is rare and is most often described in the setting of RhD-associated hemolytic disease of the fetus and newborn (HDFN).

A useful clue is the combination of:

an RhD-negative mother with known anti-D,
a newborn who unexpectedly types D-negative or gives discrepant D typing,
evidence of HDFN, and
a strongly positive direct antiglobulin test (DAT).

In reported cases of blocked D, the newborn's RBCs are typically heavily coated with maternal IgG anti-D and therefore demonstrate a positive DAT.

Why Does the D Typing Become Negative?

The infant's D antigen has not disappeared. Instead, maternal anti-D already bound to the neonatal RBCs can occupy or sterically interfere with D antigen sites, preventing the laboratory's anti-D reagent from producing the expected agglutination.

In other words:

The baby is D-positive, but the D antigen is temporarily being masked by maternal antibody.

An eluate prepared from the infant's RBCs may demonstrate anti-D, supporting the diagnosis of RhD-mediated HDFN.

A strongly positive DAT also complicates antiglobulin-phase testing. Tests that depend on adding anti-human globulin cannot simply be interpreted normally when the patient's RBCs are already coated with IgG.

Resolving the RhD Type

When blocked D is suspected, the laboratory may remove the antibody coating from the neonatal RBCs and then repeat D typing.

Several techniques have been reported, including gentle heat elution, acid elution, chloroquine-based methods, and glycine-EDTA treatment. After sufficient antibody removal, the DAT can be repeated and the RBCs retested with anti-D reagents. Published cases have demonstrated conversion from an apparently D-negative result before elution to clearly D-positive typing afterward.

The specific method used should follow the laboratory's validated procedure, since antibody-removal techniques differ in their ability to preserve red-cell antigens.

Where available, RHD genotyping can also help resolve an unexplained or unreliable serologic D result because it is not affected by antibody coating of the RBC surface.

Why Does It Matter?

Blocked D can create a confusing laboratory picture. An infant born to an RhD-negative mother with anti-D may appear to be RhD-negative even while showing clinical and laboratory evidence of immune hemolysis.

Recognizing the discrepancy is therefore important. Maternal antibody history, neonatal DAT results, hemoglobin, bilirubin, reticulocyte count, and other evidence of hemolysis should be considered together rather than relying on the initial RhD type alone.

When neonatal testing includes ABO/RhD typing and a DAT, unexpected results should be investigated before the RhD type is interpreted as definitive.

Importantly, blocked D itself is not an indication for exchange transfusion. Treatment is determined by the severity of HDFN—particularly the degree of anemia and hyperbilirubinemia. Severe disease may require phototherapy, RBC transfusion, or exchange transfusion. When anti-D is responsible, transfused red cells should lack the antigen corresponding to the maternal antibody and otherwise meet neonatal transfusion requirements.

Although blocked D is rare, it is an excellent example of why blood-bank results sometimes need to be interpreted in clinical and immunohematologic context rather than taken at face value.

Sickle Cells on a peripheral blood smear

Blood Banks are no stranger to patients with Sickle Cell Anemia. Many patients are chronically transfused, and many of us have been there for emergent Red Blood Cell exchanges due to acute chest, stroke, etc. What you might not have been a part of is a Sickle Cell patient experiencing Fat Embolism Syndrome.

What is a Fat Embolism?

A fat embolism is exactly as it sounds, it's fat or globules of fat that for one reason or another enter the bloodstream circulation and act as a embolism (vasculature occlusion caused by a clot or similar). While not common, fat embolisms are usually seen in trauma with orthopedic / long bone fractures, such as tibia, fibula, femur, pelvis, etc. It can also be seen in patients with pancreatitis.

Fat Embolism Syndrome in Sickle Cell patients

Certain populations of Sickle Cell patients may be at risk for Fat Embolisms as well.

Fat Embolism Syndrome describes a situation in which Bone Marrow Necrosis occurs as a result of the patients Sickle Cell Disease. The necrosis is not fully understood but it's hypothesized that the microvasculature in the bone marrow may become occluded, leading to cell damage and death. As the Bone Marrow is necrosed, it is thought that this could lead to fat emboli being released into circulation, causing occlusion of vessels. Another theory proposes that fat globules released into circulation get broken down into toxic metabolites leading to a pro-inflammatory state, as evidenced by increased levels of CRP, cytokines, and free fatty acids in serum. These metabolites can be responsible for many of the symptoms seen in Fat Embolism Syndrome.

Patients may have shortness of breath/respiratory distress, tachycardia, neurologic changes from confusion up to coma, petechial rash, pain, fever, hepatic damage (with resulting jaundice), decreased urine output, etc.

Interestingly, patient's with more severe homozygous Sickle Cell Disease (HgbSS) are less likely to experience Fat Embolism Syndrome. Heterozygous Sickle Cell Disease such as HgbSC or HbS/ß-Thalassemia has a higher likelihood of exhibiting Fat Embolism Syndrome propensity. The thought behind this is that with heterozygous Sickle Cell Disease, patients tend to have a higher baseline hematocrit, and thus have a higher blood viscosity than that of a HgbSS patient whose hematocrits tend to trend on the lower end. This increased viscosity can lead to decreased perfusion and thus more damage, causing increased necrosis. HgbSC patients tend to have increased inflammatory issues as well, compared to their HgbSS counterparts.

Fat Embolism Syndrome Treatment with Apheresis

The Apheresis department plays a role in helping to treat Fat Embolism Syndrome. Essentially, the first line treatment of Fat Embolism Syndrome caused by Bone Marrow Necrosis in Sickle Cell Disease is to perform a Red Blood Cell exchange. This helps to remove the sickled cells that may be assisting in causing occlusions along side of the fat globules, but based on density, should also remove a portion of the fat globules as well.

Additionally, there is reason to believe that following up with a plasma exchange could be beneficial in treating Fat Embolism Syndrome. In some patients, RBC exchange is not enough. This study explores this idea. Given that there may be a biochemical component to Fat Embolism Syndrome, such as the increased inflammatory mediators, cytokines, free fatty acids, toxic lipid metabolites, etc., it makes sense that plasmapheresis would be beneficial in removing these from the plasma.

Have you come across a patient with FES?

PFAS and the Blood Bank -- How are they related?

Don't bust out the Optia in hopes of therapeutic PFAS level reduction apheresis just yet... however...

What are PFAS?

Are PFAS the new asbestos? You may have heard the term "forever chemicals" before. This buzzword generally refers to PFAS or Per- and polyfluorinated alkyl substances. They are deemed to be "forever chemicals" due to their propensity to hang around in the environment for an extraordinarily long period of time, seemingly forever due to them containing a strong Carbon-Fluorine bond, which lends to their "immortality". They are easily able to leach into soil and nearby waters where they pose a health risk to life.

PFAS are found in all branches of industry from textiles, fire-fighting foam, furniture, packaging, non-stick surfaces, hydrophobic surfaces/materials, paper or cardboard coating, electronics, automotive, cables, tray liners, medical products, etc. The list goes on. We are certainly not free from PFAS exposure.

Exposure to PFAS is known to cause deleterious effects to living beings. Originally, they were thought to be relatively harmless, however, repeated exposure to PFAS raises concentrations within the body to a toxic level. As PFAS usage in materials increased, so did the knowledge that PFAS may be more harmful that originally thought.

PFAS exposure may cause:

Certain cancers, especially Kidney and Testicular.
Liver disease and liver damage (may be one of the reasons Non-Alcoholic Fatty Liver Disease is increasing in the population)
Thyroid disease and/or dysfunction.
Developmental defects in fetus
Fertility issues in women
Increase in pregnancy complications
Increased cholesterol levels
Ulcerative colitis
Immune system damage/dysregulation

Studies are looking into other toxic manifestations of PFAS exposure

Blood donors who have elevated serum PFAS levels are not excluded from donating blood. PFAS are everywhere, and no threshold has been given that poses an increased risk to recipients of donated blood products. Blood authorities such as AABB and FDA should continue to monitor the evidence on the possible health effects of PFASs and consider the possible implications of increased PFAS levels in blood donors.

Plasma Donation and PFAS

An interesting new study out of Australia has shown a meaningful reduction in serum PFAS levels after donation of whole blood or plasma. The study followed Australian firefighters who regularly come in contact with PFAS through their regular use of firefighting foam which harbors large concentrations of PFAS. It has been noted in the past from other studies that firefighters typically have a higher serum PFAS level than other populations.

Throughout the year of the study, significant reduction of serum PFAS levels were observed in the firefighters who donated blood and plasma. A greater reduction of PFAS levels was seen in those who donated strictly plasma, however blood donation significantly lowered levels as well.

This is certainly an interesting discovery, given the ubiquitous nature of PFAS and difficulty in removing them from our environment once they are already there. More studies are needed to further elucidate this effect. While removing PFAS from manufacturing as a whole is the best way to remedy the situation, this can certainly be a potential valid way for those in consistent high risk groups to lower their risk of experiencing toxic PFAS effects.

It is worth noting that there are no suggested limits or guidelines as far as PFAS levels in plasma go. For all intents and purposes, blood or plasma from donors regardless of PFAS level is currently accepted into blood bank inventory. It will be interesting to see how, if at all, this will be handled in the future. It is also probably unlikely that transfusing units of blood or FFP from donors with elevated PFAS levels will increase the recipients levels to a toxic level, but again, further studies can help flesh this out. Perhaps regular plasma donation for manufacturing/research purposes, rather than transfusion purposes would be the best route for these populations to take.

Perhaps in the future therapeutic plasma exchange will be an indication for toxic PFAS exposure? Who knows!

What is anti-LW?

Not to be confused with Lutheran or Lewis, Anti-LW antibodies, named after Karl Landsteiner and Alexander Wiener, are generally thought to be nuisance antibodies in the transfusion medicine world, with little impact on clinical outcomes to patients in regard to transfusion and Red Cell survival. However, their true identification is important for certain populations of people, such as pregnant women.

Anti-LW antibodies often manifest with an Anti-D pattern on antibody screen / panels. The reason for this is that LW glycoproteins are expressed at an increased rate on Rh positive Red Blood Cells. It is posited that the LW glycoprotein actually requires interaction with the Rh proteins to properly express itself on the Red Blood Cell. Thus Rh negative cells express little to no LW glycoprotein. As a result, RhD positive cells will usually react much stronger with an Anti-LW antibody. RhD negative cells will usually react much weaker or not at all depending on LW expression. So we can see that, even though LW and RhD antigens are not related from a genetic standpoint, they are phenotypically related in that they may produce apparent Anti-D reactivity.

The LW blood group system (also potentially known as ICAM4 or Intercellular Adhesion Molecule-4) consists of 3 known antigens -- LWa, LW(b), and LWab. LWa is extremely common (greater than 90% of most populations). LWb is a low frequency antigen, and LWab even less.

Most anti-LW antibodies are IgG in nature and generally exist as an autoantibody. They are not known to activate compliment. Allo-Anti-LW is extremely rare but has been known to occur in only a few patients, those who are Lwa(-)Lwb(-) are most at risk of developing an alloantibody.

Anti-Lw antibodies are often seen in certain populations where expression of Lw antigens is transiently suppressed. Some pregnant women and those with certain hematologic malignancies may suppress their Lw expression, this can cause a temporary Anti-Lw(a) or Anti-Lw(ab) to be produced. It has been observed that the antibody reactivity clears up once pregnancy or disease state has passed.

Allo Anti-Lw has been implicated in a single known potential instance of HDFN, which was relatively mild. Cases of autoanti-Lw do not result in hemolytic transfusion reactions. However, to obtain a compatible crossmatch, it may be necessary to transfuse Rh negative blood, given Lw expression is lower on Rh negative cells. Transfusion of RhD positive cells likely would not result in hemolysis or decreased RBC survival, but each transfusion center will have its own rules on how it deals with Anti-Lw transfusion.

Why is it important to differentiate between D and LW?

Anti-LW will usually present itself in an RhD positive patient with a positive autocontrol and positive Direct Antiglobulin Test (IgG/Coombs).

Knowing whether it is a real Anti-D vs Anti-LW is important for transfusion requirements, as well as for pregnant mothers. If someone has a partial D antigen, it is possible for them to create an Anti-D while still showing as RhD positive. Once the Anti-D is created, they must received RhD negative blood, because this is a real allo-Anti-D create in response to the immune system seeing epitopes of the RhD antigen not made by the recipient.

Likewise, it is important to know whether a pregnant mother has or does not have an Anti-D, as this can affect whether or not they receive RhD isoimmunization prophylaxis through the use of Rho(D) immune globulin, such as RhoGAM. Misidentifying an Anti-LW could lead to a mother not receiving this prophylaxis which could potentially result in RhD isoimmunization down the line causing HDFN is future offspring.

How do you differentiate between Anti-D and Anti-LW?

Most hospital Blood Banks are not going to have LWa/LWb,LWab antisera or similar. There are indeed some tests that a normal hospital Blood Bank may be able to perform to differentiate between D and LW.

For those hospitals at that perform DTT (Dithiothreitol) testing on Daratumumab (Anti-CD38) patients to "see underneath" the non-specific pan-agglutination that Anti-CD38 therapy causes, you already have a valid test in house! 0.2M DTT will denature the LW antigens but will NOT denature the RhD antigen. If LW is suspected, after DTT treatment of selected RhD positive cells, panel reactivity should be significantly reduced or outright removed. This is a sign that the LW antigens were disrupted.

Additionally, for those that do not perform DTT testing, but do receive umbilical cord blood for newborn testing, this can be used as a differentiator tool as well. Cord Blood exhibits high level of LW antigen expression regardless of RhD status. Thus, comparing to reactivity against adult RhD negative cells vs newborn RhD cells should show a difference. The adult cells should barely or not react at all, whereas the newborn RhD negative cells should still show quite a strong positive.