OFFICIAL CRAM TIME

What are the characteristics of delayed haemolytic transfusion reactions?

more common

haemolysis occuring > 24hours after transfusion

extravascular haemolysis in RE(reticular endothelial) system

after secondary exposure to antigen

What are the causative antibodies of delayed haemolytic transfusion reactions?

Anti-Jk^a, Rh, Kell, Duffy antibodies

What are the laboratory investigations of delayed haemolytic transfusion reactions?

DAT +

positive antibody ID

elution studies

spherocytes

decreased haptoglobulin

increased serum bilirubin

Describe the charactertics and cause TRALI.

Transfusion-related Acute Lung Injury

symptoms within 2-6 hours of transfusion completion

• fever, chills, respiratory problems, hypotension, hypoxemia > respiratory failure

What is the pathophysiolgy of TRALI?

PATHOPHYSIOLOGY:

• aby in donor plasma biind to HLA/HNA on recipients granulocytes > granulocyte activation

  • basement membrane destruction

  • increased permeability of pulmonary circulation

  • leakage of high-protein fluid into the lungs

  • > pulmonary oedema

Describe the characteristics of TACO?

Transfusion-Associated Circulatory Overload

withint 1-2 hours of transfusion

symptoms: dyspnoea, orthopnea, cyanosis, tachycardia, pulmonary oedema, hypertension

elderly, paediatric and anaemic patients

treatment: O2, diuretics

prevention: transfuse slowly

How is TRALI prevented?

Anti-HNA/HLA more common in women who have been pregnant

= only male plasma is collected

if woman has been previously pregnant > plasma but be tested neg

Compare and contrast TRALI and TACO

TACO: 1-2 hours of transfusion

TRALI: 2-6 hours of transfusion

Discuss the causes and prevention of transfusion-transmitted infections.

Causes: Donor, contamination

Treatment/further testing: antibiotics, culture and Gram stain

What is FNHTR?

Febrile Non-Haemolytic Transfusion Reactions

symptoms: increase temp after transfusion, chills, increase respiration headache

Treatment: Acetominophen

Prevention: Leukodepletion

What is the pathophysiology of FNHTR?

• cytokine released from dono leukocytes

• Anti-HLA/HNA abys in recipient bind and activate leukocytes in donor units

What is TA-GvHD?

Transfusion-Associated Graft vs Host Disease

VERY RARE

Symptoms: rash, fever, liver dysfunction > results in bone marrow aplasia

Diagnosis via HLA typing

What is the pathophysiology of TA-GvHD?

• immunocompetent T-lymphocytes in donor are transfused into shared HLA or immunocompromised recipient

• Donor lymphocytes engraft and proliferate in recipient BM
  Recipient HLA class II and/or minor histocompatibility Ags are present to donor lymphocytes > activation

• cytokines release and cytolytic activity

Explain why platelet transfusion is the leading cause of transfusion-transmitted bacterial infections?

Platelets are stored at RT

Discuss the steps taken in the laboratory in the investigation of a transfusion reaction

stop transfusion immediately

monitor vitals

maintain IV access

bacterial/viral > contact ARCBS

SEND

• transfusion reaction investigation request

• post-transfusion blood sample

• first post-transfusion urine sample

• remainder of bag being transfused/anything that was used

What are some of the adverse donation effects?

• Vasovagal

• haematoma

• allergy

• Fe deficiency

• apheresis (most common: Citrate toxicity)

What type of adverse tranfusion reactions are there?

Immune

• acute

• delayed

• allergic

• TRALI

• FNHTR

• TA-GvHD

Non Immune

• TACO

• infections

Define Acute haemolytic Transfusion reaction

• complement-mediated intravascular haemolysis

  • complement activate > C3a and C5a release > mast cell activation > histamine and serotonin release

  • FactorXIII activation > bradykinin production > vasodilation and increase EC permeability > hypotension

  • EC activation and damage > TF exposure > DIC

Usually ABO incompatabilities

What tests are performed for adverse transfusion reactions?

• IAT cross match

• Gram stain and culture

• ABO/Rh(D) group, aby screen DAT on pre and post transfusion samples

• HLA/HPA/HNA antibody testing (TRALI suspecting)

• Brain natriureic peptide (BNP)

  • decrease [TRALI] vs increase [TACO']

What are the characteristics of an infection via Hb transfusion?

bacterial, viral, parasitic

symptoms: fever, chills, vommiting

Bacteria sources: Donor or contamination

List the steps involved in pre-transfusion testing.

• maximise the benefit to the recipient while minimising risk

  • performed before administration of a blood component that could result in the transformation of antigen-antibody complexes.

STEPS:

• sample collection (request form, collection, appropriate sample)

• ABO and Rh(D) grouping

• Antibody Screen (ID if required too)

• Selection of appropriate donor

• Cross-match

• Tranfsufino

Explain the importance of the date/time of collection and phlebotomist signature on the sample tube and request form for TS samples.

date/time > location

name/contact details of requestor > obstetric hx

test/blood product required > known abys

diagnosis/indications for blood > transfusion hx

date/time required

Explain the scenarios where samples for TS testing are valid for 72 hours, and 7 days.

• patient not transfused or pregnant in the last 3 months > sample valid for 7 days from collection

• patient has been transfused, is/has been pregnant in the past 3 months > sample valid for 72h from collection — due to anamnestic (secondary) IR

Why do we perform an antibody screen, and how one is performed?

performed to detect clinically significant antibodies that may be present in the patient plasma.

• can cause haemolysis of corresponding antigen pos cells > HTR or HDNB

  • anti-a, anti-b and anti-ab is considered clinically significant

• use antibody screening cell panel

  • 2/3 cells from different donors that have known antigen expression

What are the characteristics of the cells used in an antibody screen?

• come from different group O donors

• combined must express:

  • C, c, D, E, e, M, N, S, s, K, k, Fy^a, Fy^b, Jk^a, Jk^b, Le^a and Le^b

• one should be R1R1 and the other should be R2R2

• homozygous pairing cells must be represented as those antigens demonstrate dosage

  • S, s, Fy^a, Fy^b, Jk^a, Jk^b

You perform an antibody screen there is no reaction with the three cells and the reactions are validated with AHG control cells. What is your interpretation of these results?

invalid test

• check sample

• check water bath is set @37°C

• perhaps didn't follow steps properly

Explain donor RBC selection in individuals with and without antibodies.

• should have same ABO and Rh(D) group as patient

• if recipient has EVER produced a clinically significant antibody, RBCs that do not express corresponding antigen should not be chosen > aka “antigen negative cells”

  • if not clinically sig antibody is present - use IAT cross-match compatible cells

Explain when it is appropriate to perform cross-matches by IS and IAT

cross match is done to ensure donor RBCs will not be destroyed when transfused into patient(recipient)

IS: confirms ABO compatibility only

• method used ONLY if recipient has NEVER had a clinically significant antibody detected in plasma

IAT: confirms ABO and other blood groups compat

• method used if clinically significant antibody has EVER been detected in the recipient plasma

What is blood is given during a transfusion emergency? Explain the protocol

O Rh(D) neg blood is initially given

• provide group specific blood asap

• complete pre-transfusion testing asap

  • 10min — ABO and Rh(D) group

  • 30min — aby screen and cross-match

Define Group and Screen (Group and Hold)

• ABO/RH(D) group and aby screen is performed prior to potential transfusion (i.e. elective surgery)

  • selection od unit and cross-match is performed when unit is requested

Why are donors in australia voluntary and unpaid?

maintain safe bloos supple and ensure donors have no ill effects from donation

What are the two types of donation and what can be produced from each?

Whole blood:

• all blood components are collected via antecubital vein

• separated to produce individual components

• 90 day cycle

Apheresis

• blood collected into apheresis machine

• blood is separated

• plasma/platelets are collected and RBCs returned to donor

• 2-4 week cycle

Describe the processing of whole blood for transfusion component production?

1. whole blood

2. centrifugation

3. separated into RBCs, Plasma and Platelets > maco-press blood separator — separates blood components into different bags

4. RBCs

   1. leukoreduced to minimise no of white cells present + decreases incidence of certain adverse transfusion reactions

   2. additive solution added

5. plasma is separated into plasma and Cryoprecipitate

6. buffy coat in initial centrifuged bag adds platelet additive solution (PAS). washes with pas are added to another bag > centrifuge > maco-press

What is the benefit of apheresis donation for component production?

can be performed on a more regular basis

components don’t require further processing

In which circumstances are transfusions appropriate, and inapproriate?

appropriate:

• blood loss

• anaemia [Hb] < 70g/L

• replacement of cells

• replacement of specific factors

inappropriate:

• undiagnosed or asymptomatic anaemia

• post-op Hb > 80g/L

• reversible short-term anaemia

• anaemia responsive to therapy

• improve general “well-being”

How much should 1 unit of RBCs increase an adult [Hb] by?

10g/L

How much should 1 unit of RBCs increase an adult [plt] by?

20-50 × 10^9/L

What is the shelf life of RBCs? Platelets? Fresh frozen plasma?Why is the platelet shelf life shorter?

RBCs: stored @2-6°C max 42 days.

• must be transfused within 30min of removal from storage

Platelets: stored @20-24°C max 5 days

• indications:

  • postop bleeding [plt] <50 × 10^9/L

  • thrombocytopenia if [plt] < 10 × 10^9/L

Fresh frozen plasma: stores @-25°C

• thawed and transfused within 5 days

• indications:

  • coagulopathies

  • bleeding patients who require factor replacement

  • warfarin OD

Cryoprecipitate: stored @-25°C

• indications:

  • decreased plasma

  • dysfibrinogenaemia

  • disseminated intravascular coagulation

What are the indications for FFP and Cryprecipitate administration?

• plasma exchange

• prevent bleeding

• stop bleeding

What is Apheresis

separation of cellular elements from plasma

• can be used therapeutically

  • plasma exchange i.e. treatment of immune conditions

  • RBC exchange i.e sickle cell disease

What does ISBT128 labelling stand for

Information Standard for Blood and Transplant

What are the main 3 coagulation factor concentrates?

Biostate:

• contains factor VIII and von Willebrand Factor

• Treatment for von Willebrand disease

Prothrominex-HT

• contains factors II, IX and X

• Treatment for warfarin reversal

Monofix:

• contains purified factor IX

• Treatment for Haemophilia B

Describe the pathophysiology of HDN.

1. antigen neg mother carries antigen pos child (father is antigen pos)

2. mother is exposed to baby’s RBC's (during delivery)

3. mothers immune system stimulates IR against foreign antigen (baby’s) > IgG antibody

4. during pregnancy- IgG aby crosses placenta + enters foetal circulation

   • maternal IgG aby binds to foetal RBCs

5. foetal RBCs coated in Aby are destroyed via foetal reticuloendothelial system

Which antibodies commonly cause HDN?

most common: Anti-D, Anti-K

but any from:

• Rhesus blood group

  • anti-c, C, e, E

• Kell blood group

  • Anti-k

• Duffy blood group

  • anti duffy a

Describe how an antibody titre is determined.

dilutions of plasma are reacted against cells with homozygous expression of antigen being tested

• titre is clinically sig if ≥32 or rises by 2 dilutions

Summarise the serological testing required during the antenatal and post-natal periods.

Mother:

• ABO/Rh(D) group, aby screen/ID (if not performed already)

• determine degree of foetomaternal haemorrhage (FMH) if Rh(D)neg mother is delivering Rh(D)pos baby

Foetus:

• if mother is Rh(D)neg or has a clinically significant antibody > ABO/Rh(D) group, elution studies, Hb, bilirubin

Explain how Rh(D)Ig is used in the prevention of HDN. Include the challenges faced in Rh(D)Ig administration.

Prophylactic Rh(D)Ig is isolated from plasma of Rh(D) neg individuals who produce anti-D. It can cross the placenta

given to Rh(D)neg mothers w/o immune production of anti-D

100IU of Rh(D)Ig protects against 1mL if foetal RBCs

• given 625IU @ 28 weeks

  • note: administer Rh(D)Ig after collection of sample for baby screen

• given 625IU @ 34 weeks

• given 625IU @ delivery

  • if newborn is Rh(D)+ve

Challenges:

• anti-D is highly immunogenic

• may cause HTR/HDNB

What is HDN and its charcteristics?

Haemolytic Disease of the Newborn

• HDNB, HDFNB (f=foetus)

characteristics:

• jaundice

• positive DAT

• maternal antibody

leads to:

• Kernicterus - bilirubin accumulation in the brain > brain damage

• Hydrops fetalis - oedema in the foetus > death from heart failure

What does HDN lead to?

leads to:

• Kernicterus - bilirubin accumulation in the brain > brain damage

• Hydrops fetalis - oedema in the foetus > death from heart failure

What antenatal and postnatal practice is done for HDN recognition?

First-trimester visit

• ABO/Rh(D) typing

  • re-rest at 28 weeks

• Antibody screening

  • neg > re-test at 28 weeks

  • pos >

    • perform Aby ID,

    • determine its clinical significance

    • paternal/foetal genotype/phenotype

    • aby titration

What test is done for foetal anaemia?

Middle cerebral artery (MCA) Doppler ultrasound

• non-invasive

• measures velocity of blood flow in middle cerebral artery

• increase blood flow > anaemia

How is foetomaternal haemorrhaging quantified?

Acid Elution Test (Kleihauer Test)

Flow cytometry

Explain Acid Elution Test.

• Adult haemoglobin (HbA) is sensitive to acid, foetal haemoglobin (HbF) is resistant to acid

• Expose blood film to acid

  • HbA denatures, HbF intact > stain w eosin/erythrosine

  • light pink/clear cells > HbA aka. ghost cells

How is the Kleihauer (Acid Elution Test) calculated?

Foetal RBCs(mL) = (HbF per FOV / HbA per FOV) x 2400

• ensure there are 100 HbA in 40x FOV

• based on the assumptions:

  • foetal RBCs are 22% larger than adult RBCs

  • only 92% of foetal RBCs are stained

  • maternal RBC volume is 1800mL

How to you calculate foetal RBCs via Flow cytometry

Foetal RBC(mL) + % foetal cells x 21.96

• based on assumptions:

  • foetal RBCs are 22% larger than adult RBCs

  • maternal RBCs volume is 1800mL

• more accurate, better reproducibility and less laborious than Kleihauer

What are the treatments for HDN?

Phototherapy: expose newborn to blue light (460nm)

• breaks down bilirubin

Exchange Transfusion: exchange foetal blood to remove aby and reaplce RBCs

• rarely performed as its performed in utero to allow foetal lungs to develop

What are the 2 methods of Rh(D)Ig administration?

Intramuscularyyly (IM)

• Rh(D) Immunoglobulin-VF

• 250IU and 625IU are available

Intravenously (IV)

• Rhophylac

• 1500IU

Explain the principle of the AHG test.

• used to detect

  • IgG antibodies bound to RBCs that are not detectable by other methods

  • Complement proteins bound to RBS due to antibody binding

• use anti-human IgG and/or anti-CD=3d antibodies to cross-link IgG or C3d already bound to RBCs > haemagglutination

Why is the wash step important when the AHG test is performed in tubes?

Removes IgG that is not bound to RBCs otherwise AHG reagent will bind to IgG that is free in the plasma > false negative result

When are AHG control cells added to the AHG test? Why?

add to every negative reaction

ensures that:

• AHG reagent was added to tubes

• make sure AHG reagent works

• you have correctly performed your washes

Explain the difference between the DAT and IAT. When are each of the tests used?

Direct anti-human globulin test DAT

• detects aby and/or c3d bound to patients RBCs in vivo

  • haemolytic transfusion reaction

  • haemolytic disease of the newborn

  • autoimmune haemolytic anaemia

Indirect anti-human globulin test (IAT)

• detects aby bound to RBCs in vitro

  • antibody screening and identification

  • cross-matching

  • phenotyping

Why are potentiators used in the AHG test?

decrease RBC ζ-potential or surface charge to enhance IgG aby binding/agglutination + decrease distance between adjacent RBCs > Low ionic strength saline (LISS)

Explain the mechanism of action for each of the potentiators.

Low Ionic Strength Saline (LISS)

• RBCs are diluted in 0.2% saline or Low ionic additive (LIA) is added

• Glycine is present > maintain iso-osotic conditions > cells don’t burst

• reduces ζ-potential by decreasing ionic strength

• increases aby uptake during sensitisation

• allows incubation time during AHG test shorter

Polyethylene glycol (PEG)

• speeds aby binding to RBCs via steric exclusion of water molecules

• conc aby around RBCs

• allows shortened incubation time in AHG test

• NB; addition of PEG > cannot centrifuge cells until addition of saline of wash

Albumin

• increases dielectric constant of the medium > decrease in ζ-potential

• used at 22-305

• more expensive

Enzymes

• modify antigens on RBC surface

• decrease ζ-potential by removing sialic acid residues

• enhance reactivity of some blood group antigens

• decrease reactivity of others

• performed in 2 stages:

  • Stage 1: incubate plasma, RBC and enzyme > centrifuge then read results

  • Stage 2: incubate RBCs and enzyme together > wash cells > incubate plasma with enzyme-treated cells > centrifuge and read results

Polybrene

• cationic ammonium polymer that causes reversible aggregation of RBCs

• added to aggregate cells > sodium citrate then added to neutralise polybrene

  • Aby present: agglutination

  • No Aby present: agglutination will disperse

When performing the AHG test using cards, why do the samples not require washing at any point of the test?

Buffer solution of high density is layed over the top of bead:

• traps plasma proteins > no washing

Describe the three phased of the AHG test by tube method, including what is detected at each phase.

RT: agglutination @RT - IgM : not clinically significant

37°C: Some IgG antibodies (anti-Rh, anti-K)

IgM reactive @ 37°C

AHG: IgG antibody

What are the benefits of performing haemagglutination reactions in cards?

• easy to use

• require no washing

• reagents already added

For haemagglutination reactions performed in cards, describe the appearance of each of the reaction grades when using the 0-4+ scale.

Describe how agglutination occurs.

Haemagglutination

1. Sensitisation: aby binds to antigen on the RBC surface

2. Agglutination: bound antibdy cross-links adjacent RBCs

What is meant by the term “dosage”?

how antibodies react to antigens which demonstrate dosage effect

i.e. Anti-Jk^a demonstrates dosage. It reacts stronger to cells which hall homozygous expression of Jk^a

Antigens of which blood groups are destroyed by enzyme treatment?

M, N, S, s, U (MNS blood group)

Fy^a and Fy^b (Duffy blood group)

Antigens of which blood groups are enhanced by enzyme treatment?

C, c, D, E, e (Rh blood grouping)

Found on chromosome 1

• RHD gene encodes D antigen

• RHCE gene encodes C, c, E, e antigens

  • C and c differ by 6 nucleotides

  • E and e differ by 1 nucleotide

K, k (Kell blood grouping)

Jk^a, Jk^b (Kidd blood grouping)

Why are Kidd antibodies so difficult to work with?

often weak, demonstrate dosage, found in combi with other aby’s

Anti-Jk^a, Anti-Jk^b

• IgG

• best detected @37°C via IAT

• unstable on storage

• common cause of HTR, rarely HDNB

Why is there a racial difference in Duffy phenotype distribution?

absence of Duffy antigens on RBCs > RBCs more resistant to invasion by a malarial parasite

positive selection pressure

Explain the inheritance of Rh antigens.

inherited as a haplotype

one set of RHD and RHCE gene from one parent, second set from other

i.e. DCe/dce (Fisher-Race nomenclature)

Why is the D antigen so immunogenic?

contains at least 30 different epitopes

Explain the difference between the FIsher-Race and Weiner nomenclatrue.

Fisher-Race:

haplotype written as a triplet of letters

note - d isused to represent “absence of D”

• DCe/dce

  • Genotype: DCe/dce

  • Phenotype: DCce

Weiner:

uses R/r and numbers/primes to represent haplotype/ genotype/phenotype

• R = D antigen

• r = absence of D antigen

• Ce = R1 or r’

• cE = R2 or r”

• ce = R0 or r

What is the class of each of the antibodies in the MNS blood group?

anti-M/N: IgM or IgG;not clinically sig unless reactive @37°C

anti-S/s: IgG; clinically sig as react @37°C

What does RHD and RCHE gene encode?

417 aa transmembrane

non-glycosylated proteins

Describe the characteristics of Rh antibodies.

Immune

usually IgG

dont bind complement

react optimally @RT

Detect using IAT (“Weak D Test”

How should Partial D be expressed?

Recipient: Rh(D) neg

Donor: Rh(D) pos

Describe Kell blood group system antigens.

2 antigens(proteins) : K and k (cellano)

• Antithetical pair expressed co-dominantly

• well developed at birth

• K is highly immunogenic

• K-k+ most frequent

Antibodies

• Anti-K

  • IgG

  • can cause HTR and HDNM

  • best detected @37°C via IAT

• Anti-k

  • very rare > difficult to find compatible blood

  • IgG

  • best detected @37°C via IAT

Describe Kell blood groups antibodies.

• Anti-K

  • IgG

  • can cause HTR and HDNM

  • best detected @37°C via IAT

• Anti-k

  • very rare > difficult to find compatible blood

  • IgG

  • best detected @37°C via IAT

Describe Kidd blood groups antigens.

2 main antigens: Jk^a, Jk^b

• protein

• antithetical pairs expressed c-dominantly

• well developed at birth

• poor immunogens

Describe MNS blood group antigens.

5 main antigens: M, N, S, s, U

• protein

• M/N expressed on glycophorin A (GPA)

  • furthest away from RBC membrane

• S/s and U expressed on glycophorin B (GPB)

  • closest to RBC membrane

Describe Duffy blood group antigens.

2 main antigens: Fy^a and Fy^b

• antithetical pairs expressed co-dominantly

• well developed at birth

What is a blood group, and what are the ISBT blood group requirements?

one or more RBC surface antigens controlled b an allelic gene.

ISTB requirements

• antigen must be inherited

• the gene encoding it must have been:

  • identified and sequenced,

  • chromosomal location must me known

• gene is different from other gene encoding antigens of existing blood group systems

• corresponding human alloantibody must be identified

What are the two main types of RBC antigen?

1. anti-a

2. anti-b

Explain the difference between an antigen and antibody

Antigen : produces and immune response (antibody) if recognised as foreign

Antibody : specific proteins produced in response to an antigen. only interact with specific part of the antigen before production

What are the two main subtypes of antibodies encountered in transfusion science? What are the kinetics of their production?

IgG & IgM

Kinetics :

• Primary Challenge

  • long lag time (5-7days)

  • IgM predominant

  • some IgG

  • Memory B cell development

• Secondary Challenge

  • Anamnestic Response

  • short lag time (2-3d)

  • IgG predominnat

  • some IgM

  • High Avidity

Define, and explain the characteristics of, naturally occurring and immune antibodies.

Present in plasma without any known immunisation

• not present at birth

IgG : ~12nm, monomer, react @37°C, “incomplete”

• e.g. Anti-Rh, Anti-Kell

IgM : ~30nm, penteramic, react @4°C, “complete”

• e.g. anti-A, anti-B

What is in in vivo consequence of antigen-antibody binding in the transfusion science context?

RBC is damaged:

• leads to complement activation > Antibody-dependent cell-mediated cytotoxicity (ADCC(lysis))

Haemolytic Transfusion Reaction (HTR)

Haemolytic Disease of the Newborn (MDNB)

Describe the mechanism of haemagglutination for IgG and IgM antibodies.

1. Sensitisation

2. Agglutination

IgG

1. Sensitisation > Aby binds to cells

2. Agglutination > Add anti-IgG to cross-link cells

IgM

1. Sensitisation > Abyb binds to cells

2. Agglutination > Bound aby cross-link cells

Describe the appearance of each of the reaction grades used in the 0-4+ haemmagglutination grading scale.

0 — no agglutinates

1+ — small agglutinates w red background

2+ — many medium-sized agglutinates

3+ — one or two large agglutinates

4+ one large agglutinate

Explain how ADCC is stimulated.

• Medianted by IgG

• aby-coated RBC binds to macrophage via Fc receptor > extravascular haemolysis

Which antigens and antibodies are produced on each of the ABO groups, and what is their distribution in the Australian population?

A : 39%

B : 11.5%

AB : 3.5%

O : 46%

Describe the production of the ABO antigens.

Type II precursor substance (CHO) + glycosyltransferase + —> H antigen

H antigen

• A or B antigen

Describe the characteristics of ABO antibodies.

• “Naturally occurring” - produced w/o priir exposure to antigen

• Usually IgM but can be IgG (Anti-a,B in O people is IgG)

• Bind complement

• React optimally @ RT

• Not detected until 3-6 months of age

Describe how an individual’s ABO group is determined

Forward Grouping

• react patients RBCs with known antiserum (anti-a or anti-b)

• identifies which antigens are present

Reverse Grouping

• react patients plasma with cells of known phenotype (A cells or B cells)

• identifies which antibodies are repesent in patient plasma

Draw a table describing which ABO groups are compatable