What is the Difference Between Conjugated and Unconjugated Bilirubin?

Bilirubin is a biochemical parameter of your liver function test. Your doctor uses this tool to diagnose liver disease.
In the human body, bilirubin is a waste product of your hemoglobin produced during the red blood cells breakdown in the spleen.

Although bilirubin does not have a specific function, it is generally a component of bile juice. It is also called a bile pigment, which is yellow in color.

There are two forms of bilirubin in our blood.

One is unconjugated bilirubin, which forms during the breakdown of red blood cells, and the other is conjugated, which starts during metabolism in the liver.

The unconjugated bilirubin is a catabolic product of red blood cells. This non-conjugated compound is also known as indirect bilirubin.

Some possible reasons or diseases associated with unconjugated hyperbilirubinemia –

1. Hemolytic anemia
2. Neonatal Jaundice
3. Genetic factors
4. Drug induced unconjugated hyperbilirubinemia

On the other hands, Conjugated bilirubin is generally formed after the glucuronidation of the unconjugated bilirubin.
The conjugation process occurs in your liver and converts your unconjugated bilirubin into conjugated bilirubin. This type of glucuronidation compound is also known as direct bilirubin.
In simple words, direct bilirubin means conjugated bilirubin.

The elevated conjugated bilirubin indicates Conjugated hyperbilirubinemia.

This condition is most commonly seen in cholestatic liver disease.

Cholestatic is a medical condition where the flow of bile juice gets reduced or stopped. You may have this cholestatic liver disease in two forms – Intrahepatic and extrahepatic obstruction.

In this article, we will discuss bilirubin, metabolism of bilirubin, normal range of bilirubin, and its clinical relevance. Further, we will also know the difference between conjugated and unconjugated bilirubin.

1. WhatistheDifferenceBetweenConjugatedand
UnconjugatedBilirubin?
PostedBySUMITSHARMA
Contents
❖Introduction
❖Whatisbilirubininabloodtest?
❖Howisbilirubinformedfromthebreakdownofhaemoglobin?
❖Whatisunconjugatedbilirubin?Whatdoesahighlevelofunconjugatedbilirubinindicate?
1.HaemolyticJaundice
2.NeonatalJaundice
3.Geneticfactors

2. 4.Drug-inducedunconjugatedhyperbilirubinemia
❖Whatisconjugatedbilirubin?Whatcauseshigh-levelconjugatedbilirubin?
1.Intrahepaticbiliaryductobstruction
2.ExtrahepaticBiliaryDuctObstruction
❖Whattriggerscholestasisofpregnancy?
❖WhatisthedifferencebetweenConjugatedandUnconjugatedBilirubin?
❖Howtocalculateconjugatedandunconjugatedbilirubin?
❖Conclusion
❖FAQ
Q1.Whatistheroleofbilirubin?
Q2.Whatformofbilirubinisfoundinblood?
Q3.Whatisthedifferencebetweendirectandconjugatedbilirubin?
Q4.WhatisthedifferencebetweenConjugatedandUnconjugatedHyperbilirubinemia?
Q5.Whatarethe3typesofjaundice?
Q6.Isjaundicefromconjugatedorunconjugatedbilirubin?

3. Introduction
Areyoucurioustoknowthedifferencebetweenconjugatedandunconjugated
bilirubin?
Wheneveryouhavealiverproblem,yourdoctorsuggestsaliverfunctiontest.You
musthavefoundconjugatedandunconjugatedbilirubinlevelsinyourreport.
Unconjugatedbilirubinisatoxicproductthatformsaftertheexpiryofredblood
cellsinthespleen.Whereasconjugatedbilirubinisanon-toxicproductthat
producesduringmetabolismintheliver.
Thisbilirubintestisessentialinclinicalpracticetodiagnoseliverdisease(suchas
Jaundice)andotherhealthproblems.
Inthisarticle,wewilldiscussbilirubin,metabolismofbilirubin,normalrangeof
bilirubin,anditsclinicalrelevance.Further,wewillalsoknowthedifference
betweenconjugatedandunconjugatedbilirubin.
Let’sgetstarted.
Whatisbilirubininabloodtest?
Bilirubinisabiochemicalparameterofyourliverfunctiontest.Yourdoctoruses
thistooltodiagnoseliverdisease.
Inthehumanbody,bilirubinisawasteproductofyourhemoglobinproduced
duringtheredbloodcellsbreakdowninthespleen.
Althoughbilirubindoesnothaveaspecificfunction,itisgenerallyacomponentof
bilejuice.Itisalsocalledabilepigment,whichisyellowincolor.
Therearetwoformsofbilirubininourblood.
Oneisunconjugatedbilirubin,whichformsduringthebreakdownofredblood
cells,andtheotherisconjugated,whichstartsduringmetabolismintheliver.

4. Howisbilirubinformedfromthebreakdownof
haemoglobin?
Yourredbloodcell’s(RBCs)averagelifespanis120days.After120days,RBCs
havetobedestroyed.
Thesecellsgotoyourspleen.Here,thespleenactsasalymphaticorganthatplays
avitalroleindestroyingoldRBCsbyphagocytosis.That’swhythespleenisalso
knownasthe“GraveyardofRBC“.
Generally,Redbloodcellscontainhaemoglobin.Itgetsbreakdowninto“heme”
and“globin”.
This“heme”convertsitintobiliverdinandtheneventuallyconvertsitinto
bilirubinwiththehelpbiliverdinreductaseenzyme.

5. Thisbilirubinisverytoxicandlipid-soluble(orwater-insoluble).Thistypeof
bilirubiniscalledunconjugatedbilirubin.
Yourbodydoesnotwanttostayunconjugatedbilirubininyourbloodforlong.
So,itgetsmetabolisedinyourliverandformsawater-solublecompound–
conjugatedbilirubinsothatitcanexcretequicklyfromyourbody.
Therefore,onceunconjugatedbilirubinentersyourblood,itgetsattachedto
albumin,whichflowsinyourblood.
Here,albuminactsasatransporterthathelpsyourunconjugatedbilirubinmove
towardstheliver.
Assoonasunconjugatedbilirubinentersyourliver,itstartsmetabolizingit.
Eventually,itconvertstheunconjugatedbilirubinintoconjugatedbilirubinby
conjugationprocess(especiallyglucuronidationreactionwithUGT).
Thisconjugatedbilirubinislesstoxic,morepolarandwater-soluble.Conjugated
bilirubinisalsoanexcretorysubstancethatcomesoutwithyourbileandtravels
throughthebileduct.
Finally,itreachesthesmallintestine(duodenum).Thenitgoestothelarge
intestine,oxidisedbysomebacteriathatconvertintourobilinogen.
Urobilinogenisafinalbilirubinproductthatexcretesfromthebodythroughurine
andfaces.

6. Whatisunconjugatedbilirubin?Whatdoesahighlevel
ofunconjugatedbilirubinindicate?
Theunconjugatedbilirubinisacatabolicproductofredbloodcells.This
non-conjugatedcompoundisalsoknownasindirectbilirubin.
So,indirectbilirubinmeansunconjugatedbilirubin.
Yourbloodtestreportshowsanindirectbilirubinnormalrangeof0.2to0.8
mg/dL,whichmayvaryfromlabtolab.
IfyougetyourLFTdone,youseeahighunconjugatedbilirubin(UCB)level
abovethereferencerange.ThisiscalledUnconjugatedHyperbilirubinemia.
YoumayhavehighUCBbythesethreepossiblemechanisms–

7. ●Overproductionofbilirubin
●DecreasehepaticuptakeofUCB
●Decreaseconjugationintheliver
Somepossiblereasonsordiseasesassociatedwithunconjugated
hyperbilirubinemia–
1.HaemolyticJaundice
Hemolyticanemiaisthemostcommoncauseoftheincreasedproductionof
bilirubin.
Inthistypeofanemia,youmayhaveexcessdestructionofRBCsthatcausehigh
unconjugatedbilirubinintheblood.TheliverisunabletoconjugatethishighUCB
quickly.
Duetothis,UCBgetsincreasedinyourbloodanddepositedinyourskinand
sclera,reflectingyellowishincolour.Youcanseethisclassicalclinicalsignif
serumbilirubinlevelsexceed3mg/dl.
ThistypeofhemolyticJaundiceisalsocalledPre-HepaticJaundicebecausethere
isnodirectinvolvementofthelivertocauseJaundice.
IfyouhaveJaundiceduetohemolysis,youshouldalsogowithsomeother
laboratorytestslikeHb(haemoglobin),LDH(Lactatedehydrogenase),and
haptoglobin(haptoglobinisaproteinthatbindsonfreehaemoglobin).
Youwouldseesomeimbalanceofbiochemicalparametersinyourreport–
●DecreaseHb
●IncreaseLDH

8. ●Increasehaptoglobin
2.NeonatalJaundice
YoumusthaveseenJaundiceinanew-bornbaby.
Whenachildisborn,itsliveristiny,andittakestimetomaturethelivercells.
Becauseoftheunmaturedliver,itdoesnotoccurconjugationprocess.Thiscauses
highunconjugatedbilirubininnew-bornthatleadstoJaundice.Thisisknownas
NeonatalJaundice.
AlthoughneonatalJaundiceisnotlife-threatening.Ifnottreatedwell,itcanbe
fatal.
SinceUCBistoxicandlipidsoluble.So,alipid-solublecompoundcancrossthe
blood-brainbarrier,whichleadstobraindamage.
ThisiscalledBilirubinInducedEncephalopathy(orkernicterus).
Sometimeswhenyoubreastfeedyourchild,itmayalsoincreasethelevelof
bilirubin;thisiscalledMaternalMilkJaundice.
Moreover,itmayalsocauseJaundiceifyoudon’tbreastfeedyourbabybecause
lactationfailuremayalsocauseJaundice.
3.Geneticfactors
Somegeneticfactorsarealsoresponsibleforincreasingthelevelofunconjugated
bilirubin.
Supposesomeonehasamutationinageneoflivercells.Inthatcase,thatperson
mayhavehighunconjugatedbilirubinintheblood.Itismostspecificwith
variationinUDP-glucuronosyltransferase1A1(UGT1A1)genethatcauses–

9. ●Gilbertsyndrome,and
●Crigler-NajjarsyndromestypeIorII
Theseraregeneticdisordersreducetheconjugationprocessofunconjugated
bilirubinandleadtohyperbilirubinemia.
4.Drug-inducedunconjugatedhyperbilirubinemia
Youmayhaveunconjugatedhyperbilirubinemiaifyouareoncertainmedicines
like–
●Aspirin(NSAIDs)andsulphonamides(antibiotic)
Thefreeunconjugatedbilirubinisgenerallyattachedtoalbumininyourblood.
Supposeyoutakeahighdoseofaspirinorsulphonamidemedicines;these
medicinescompetewithalbumin.
So,Aspirinandsulphonamidegetdetachedfromtheunconjugatedbilirubinfrom
albuminandattachedtothealbuminitself.Duetothis,thisfreeunconjugated
bilirubin(orunboundbilirubin)getsincreasedinyourblood.
Thishighunconjugatedbilirubinmaydamageyourbrain(orkernicterus).Itcanbe
seenmostlyinchildrenthatcausesReyeSyndrome,mainlyduetoAspirin.
●Novobiocin(antibiotic)
Novobiocinisanantibioticthathasthepotentialtocauseunconjugated
hyperbilirubinemiabyinterferinginbilirubinconjugation.
ThismedicineinhibitstheconjugationenzymeUDP-glucuronosyltransferase
(UGT).

10. ●Proteaseinhibitors(antiretroviraldrugs)
ProteaseinhibitorsareantiretroviraldrugsthatareusedinthetreatmentofHIV
infection.Butthesemedicinesarehighlyassociatedwithincreasedunconjugated
bilirubininyourblood.
TheyalsoinhibittheconjugationenzymeUDP-glucuronosyltransferase(UGT),
whichleadstoJaundice.
Someexamplesofproteaseinhibitorsincludeindinavir,saquinavir,ritonavir,etc.
Whatisconjugatedbilirubin?Whatcauseshigh-level
conjugatedbilirubin?
Conjugatedbilirubinisgenerallyformedaftertheglucuronidationofthe
unconjugatedbilirubin.

11. Theconjugationprocessoccursinyourliverandconvertsyourunconjugated
bilirubinintoconjugatedbilirubin.Thistypeofglucuronidationcompoundisalso
knownasdirectbilirubin.
Insimplewords,directbilirubinmeansconjugatedbilirubin.
Yourbloodtestreportshowsthedirectbilirubinnormalrangeof0.0to0.3mg/dL,
whichmayvaryfromlabtolab.
Supposeyoufindthedirectbilirubinabovethereferencerange,suchashigherthan
2mg/dLormorethan20%oftotalbilirubin.Inthatcase,elevatedconjugated
bilirubinindicatesConjugatedhyperbilirubinemia.
Thisconditionismostcommonlyseenincholestaticliverdisease.
Cholestaticisamedicalconditionwheretheflowofbilejuicegetsreducedor
stopped.Youmayhavethischolestaticliverdiseaseintwoforms–Intrahepatic
andextrahepaticobstruction.
Let’sdiscussthisindetail–
1.Intrahepaticbiliaryductobstruction
Whenbilejuicegetsprepared,ittravelsinnarrowbiliarytubesinsideyourliver.
ThenetworkofthesetinythintubesisknownasIntrahepaticBiliaryDuct.
Ifyougetimpairmentoranyobstructioninthesetinytubes,itwillincreaseboth
conjugatedandunconjugatedbilirubin.Inthiscondition,itcannotexcretebilirubin
fromthebileduct.ThisconditioniscalledIntrahepaticBiliaryDuctObstruction
(IHBDO).
Sometimes,itisalsocalledIntrahepaticJaundice.
Theleadingcauseofintrahepaticductobstructionishepatocellular(orliver)
injury.Thisliverinjurymaybedueto–

12. ●Autoimmunediseasessuchasprimarybiliarycholangitis(inflammationof
theintrahepaticbileduct)
●Viralhepatitis
●Alcoholichepatitis
Itcouldbeduetosepsisandexposuretobacterialinfection.Thesethingsactivate
yourimmunesystem,releasingcytokinesandinterleukins(suchasIL-1,IL-6,and
alphaTNF).
Theseinflammatorychemicalsgotoyourbileductandmakeitshrink,restricting
theflowofbile.Asaresult,conjugatedbilirubinwillnotdraintothebileduct,and
itgoesbacktoyourbloodstream.Moreover,italsohamperstheconjugation
processinyourliver.
Eventually,itwillincreasetheconjugatedandunconjugatedbilirubinlevelsin
yourblood.
Apartfromelevatedbilirubin,youwillalsonoticeahighlevelofALP(Alkaline
phosphatase)andGGT(gamma-glutamyltransferase).
Bilejuiceisamixtureofvariouscomponents.Amongthesecomponents,thereare
bilesaltslikeCholateandchenodeoxycholate.
InIntrahepaticJaundice,thelevelofbilejuiceincreases,leadingtoelevated
bilirubinandbilesaltsinyourblood.Duetothis,youmayhaveexperiencedthe
followingsignandsymptoms–
●Pruritusoritchingduetohighlevelsofbilesalts
●Yellowisheyescleraandskinduetoanelevatedlevelofbilirubin
●Lossofappetiteduetoimpairedmetabolism

13. ●Lemonyellowtoapplegreenskinduetobiliverdiniflongstanding
intrahepaticJaundice
2.ExtrahepaticBiliaryDuctObstruction
Whenbilejuiceleavestheliver,ittravelsinthewidebileducttoreachthesmall
intestine.ThesebileductsthatpresentoutsidetheliverarecalledExtrahepatic
BiliaryDuct.
Supposeyougetanyfibrosisorobstructionintheseexternalbileducts,leadingto
inflammationandswelling.
Thisinflammationcausesblockageandreducestheflowofbilejuice.Inthis
condition,yourbilejuicecannottravelinthebileduct.Asaresult,itincreasesthe
levelofconjugatedbilirubin.

14. Youwillnothaveaprobleminyourconjugationprocessbecauseyourlivercells
workwell.Duetoobstructionofthebileduct,youwillhaveconjugated
hyperbilirubinemia.
ThistypeofblockageintheexternalbileductoftheliveriscalledExtrahepatic
BiliaryDuctObstruction(EHBDO).
ItisalsoknownasExtrahepaticJaundice.Theleadingcauseofextrahepatic
Jaundiceis
●Choledocholithiasis(stoneinthebileduct)
●Benignbileductstrictures
●Cholangiocarcinoma(cancerinthebileduct)
ThelaboratoryLFTreportshowsahighlevelofdirectbilirubin,ALPandGGT.

15. Alsoread,SGOTandSGPTInLiverFunctionTest
Whattriggerscholestasisofpregnancy?
Youmusthaveseenanitchingprobleminpregnantwomenthatusuallyoccursin
latepregnancy.Thisitchingprobleminpregnancyindicatesaliverproblem,andit
iscalledIntrahepaticCholestasisofPregnancy(ICP).
Inthelastpregnancystage,pregnancyhormones(suchasestrogenand
progesterone)areattheirpeak.
Thehighsurgeofestrogenstopsbileflowintothebileduct.Asaresult,youwill
haveconjugatedandunconjugatedhyperbilirubinemia.

16. Thiselevatedbilirubingetsdepositedinyourskin,andyoumayhavepruritus(or
itchingproblem).
SomekeymarkerscanalsobeseeninICPconditions,likeelevatedALPandGGT.
WhatisthedifferencebetweenConjugatedand
UnconjugatedBilirubin?
Here,Ihavecomparedthesetwoformsofbilirubininthetablebelow.Youcansee
thesignificantdifferencebetweenconjugatedandunconjugatedbilirubin.
Features Unconjugated
bilirubin
Conjugatedbilirubin
DescriptionDoesnothave
conjugation
Conjugationoccurs
AnothernameIndirectbilirubinDirectbilirubin
SolubilityLipidsoluble Watersoluble
Typeof
compound
Non-polar Morepolar
Toxicity Toxic Non-toxic
ProteincarrierBindwithalbuminfor
transportation
Doesnotbindwith
anyprotein
Normalrangein
adult
0.2to0.8mg/dL0.0to0.3mg/dL

17. High
concentrationin
blood
Unconjugated
hyperbilirubinemia
Conjugated
hyperbilirubinemia
Clinical
relevance
Normalurinecolour
duringunconjugated
hyperbilirubinemia
Darkurineindicates
conjugated
hyperbilirubinemia
Classical
indicators
Scleralicterusand
yellowishskin
Pruritus,scleralicterus
andyellowishskin
Otherlab
parameters
AST,ALTandALP
levelsarenormalin
unconjugated
hyperbilirubinemia
VeryhighALPand
GGTlevelin
conjugated
hyperbilirubinemia
Howtocalculateconjugatedandunconjugated
bilirubin?
Ifyousumtheconjugatedandunconjugatedbilirubin,itwouldbeyourtotal
bilirubin.
Itmeansthetotalbilirubinisacombinationofconjugatedandunconjugated
bilirubin.
Totalbilirubin=conjugated(ordirect)bilirubin+unconjugated(orindirect)
bilirubin
=0.0to0.3mg/dL+0.2to0.8mg/dL
=0.2to1.1mg/dL
Thenormalrangeoftotalbilirubinis0.2–1.1mg/dlforadults.Youcancalculate
yourotherbilirubinparametersbythisformula.Forexample,

18. ●Ifyougethighindirectbilirubinaftersubtractingtotalbilirubinfromdirect
bilirubin,itindicatesPrehepaticjaundice.
Indirectbilirubin=(totalbilirubinminusdirectbilirubinlevel)
=2.5–0.3=2.2mg/dl
●Ifyougetanelevateddirectbilirubinlevelaftersubtractingtotalbilirubin
fromindirectbilirubin,itindicatesPost-hepaticJaundice.
Directbilirubin=(totalbilirubinminusindirectbilirubinlevel)
=4–1=3mg/dl
●Ifyoufindelevatedbothindirectanddirectbilirubinthatrepresentshigher
totalbilirubin.ItindicatesIntrahepaticjaundice.
Totalbilirubin=directbilirubin+indirectbilirubin
=1.1+2.1mg/dl
=3.2mg/dl
Conclusion
Bilirubinisanaturalby-productofredbloodcellswithyellowishpigment.Itis
consideredawasteproduct,anditseliminationisessential.
Wehaveseentwotypesofbilirubin–conjugatedandunconjugated.
Clinically,youwillhaveamedicalconditionifabilirubinleveliselevated.For
example–

19. ●ExcessunconjugatedbilirubinindicatesPre-HepaticJaundice
●ExcessconjugatedbilirubinindicatesEHBDOorPostHepaticJaundice
●ExcessofbothconjugatedandunconjugatedbilirubinindicatesIHBDOor
IntrahepaticJaundice
IfyoufindanyimbalanceofbilirubininyourLFTreport,youmustconsultyour
doctor.Yourdoctorwillclinicallycorrelatetheimbalancedbilirubinwithyour
symptoms.
Itwasaninformativepostaboutconjugatedandunconjugatedbilirubin.
Havequestions?
Letmeknowinthecommentsbelow.Iwilltrymybesttoanswerallofthem.
FAQ
Q1.Whatistheroleofbilirubin?
Whenyourredbloodcellsgetexpire,itproducesbilirubin.Simply,bilirubinisa
wasteproductofyourhaemoglobin.Although,bilirubindoesnothaveaspecific
roleinyourbody.Somestudiessuggestthatitactsasanantioxidantinthehuman
body.
Q2.Whatformofbilirubinisfoundinblood?
Therearetwoformsofbilirubininourblood–

20. ●Unconjugated(indirect)bilirubin–boundwithalbuminprotein
●Conjugated(direct)bilirubin–formedintheliveraftermetabolism
Q3.Whatisthedifferencebetweendirectandconjugatedbilirubin?
Directbilirubinisalsoknownasconjugatedbilirubin.Thistypeofbilirubinforms
afterconjugationwithglucuronicacidinyourliver.
Q4.WhatisthedifferencebetweenConjugatedandUnconjugated
Hyperbilirubinemia?
Anexcessamountofconjugatedbilirubininyourbloodiscalledconjugated
hyperbilirubinemia.Thisindicatespost-hepaticjaundice.Whiletheelevated
unconjugatedbilirubininyourbloodiscalledunconjugatedhyperbilirubinemia.
Thismeansprehepaticjaundice.
Q5.Whatarethe3typesofjaundice?
Youmayhavejaundiceinthreeforms–
●Pre-hepaticjaundice(duetohaemolysis)
●Intrahepaticjaundice(duetohepatocellularinjury)
●PosthepaticJaundice(duetoinflammationorobstructioninthebileduct)
Q6.Isjaundicefromconjugatedorunconjugatedbilirubin?

21. Youmayhaveanimbalanceofbilirubinindifferenttypesofjaundice,like–
●Pre-hepaticjaundice–elevationofunconjugatedbilirubin
●Intrahepaticjaundice–elevationofconjugatedandunconjugatedbilirubin
●Posthepaticjaundice–elevationofconjugatedbilirubin
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