Table Of ContentCLINICAL
CHEMISTRY
MADE EASY
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CLINICAL
CHEMISTRY
MADE EASY
Jeremy Hughes
MAFRCPEPhD
Wellcome TrustSeniorResearchFellowinClinical Scienceand
HonoraryConsultant PhysicianattheRoyalInfirmary Edinburgh,
MRC CentreforInflammationResearch,The Queen’sMedical
ResearchInstitute, Edinburgh, UK
Ashley Jefferson
MDMRCP
Clinical AssociateProfessor,Division ofNephrology,University of
Washington,Seattle,USA
Foreword by
John Iredale
DMFRCPFMedSci
Professor ofMedicine, UniversityofEdinburgh
Edinburgh London NewYork Oxford Philadelphia StLouis Sydney Toronto 2008
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Foreword
Thefunctionsofcellsaregovernedbythelawsofchemistryandphys-
ics, and biochemical reactions underlie the fundamental processes of
life. For these reasons, it is no surprise that in many countries a high
school chemistry qualification is a prerequisite for undergraduate
admission to medical school. Medical students become exposed to
biochemistry during their early training and many joke about the
impenetrability of the subject. Indeed one classmate of mine, a witty
songwriter, penned the classic ‘Don’t cry for me biochemistry, the
truth is I never learnt you’, to be sung to the tune of ‘Don’t cry for
me Argentina’, from the then hit Lloyd Webber musical ‘Evita’. Of
course,thislevitydisguisesthefactthatmedicalgraduatesinvariably
acquireagoodworkingknowledge ofbiochemicalprocess.
Having acquired a grounding in biochemistry, as clinical students
andjuniordoctorswearethenconfrontedwiththechallengeofassim-
ilatingthatknowledgewiththepracticeofmedicineandexploitingit
in clinical practice. Nowhereis that assimilation more direct than the
fieldofclinical chemistry.However,the expandingcontentofunder-
graduate syllabuses means that the time and opportunity to make
this synthesis is becoming eroded. Moreover, the integration of pre-
clinical biochemistry with the approach to clinical problems is not
always straightforward. For example, understanding the Henderson–
Hasselbalch equation and the principles underlying pH balance and
bufferingmayseemstraightforwardinabstract,butgroupingthepat-
terns of changes in pH and accompanying alterations in the PO and
2
PCO inthe bloodgasesofabreathless patientcanseem dauntingto
2
themedicalstudentandjuniordoctor.Theapproachtoclinicalchem-
istryinrealclinicalsituationsrequiresknowledge,experienceandan
integratedandclinicallyrelevantmodel.Itispreciselythisintegrated
model which Jeremy Hughes and Ashley Jefferson have brought
together inthistext.
The use of appropriate clinical context throughout the book illus-
trates how clinical chemistry tests can be deployed to rapidly obtain
information critical for the management of sick patients.This area of
medicineisnowofessentialimportancegiventhechangesinthepro-
cess of care delivery in hospitals. Junior doctors are frequently called
to see sick patients with whom they are unfamiliar, and for whom a
rapid appraisal of clinical need and diagnosis will be required. The
Foreword
armamentariumofclinicalchemistrytestsisinvaluableinthissetting
– frequently simple investigations, such as blood gas measurements,
can rapidly provide information essential to diagnosis and manage-
ment.Farfrombeingasettingneglectedbytheauthors,clearandcon-
cise guidance to the use and interpretation of tests in the emergency
setting is a particular strength of this volume. An additional area of
focusistheroleofdrugsininfluencingtheresultsofclinicalchemistry
tests and as possible causes of abnormalities in routine tests under-
takeninboththecommunityandhospitalsettings.Withtheincreasing
numberofelderlypatientswhoarealltoofrequentlyexposedtopoly-
pharmacy,thisareaalsowillassumeagreaterandgreaterimportance
inthediagnosisandeffectivemanagementofourpatientpopulation.
Thisconciseandhighlyreadabletextprovidesexactlytheinforma-
tion that senior clinical students and junior doctors need to request,
arrange and interpret clinical chemistry tests effectively, and in so
doing enhance clinical care. It is the kind of book I wish had been
available when I was a student and should be valuable to trainees
across all specialities. There is no longer any excuse for biochemistry
and clinical chemistry to be a neglected or ‘tearful’ partner in the
curriculum.
JohnIredale
Edinburgh2007
viii
Preface
Clinicians are unable to provide adequate medical care in isolation.
Theyaredependentuponnumerouslaboratorydisciplinestoassistin
the management of patients with varied medical problems. Depart-
ments of Clinical Chemistry and related departments such as Micro-
biologyandClinicalImmunologyplayaveryimportantroleinpatient
care.Theyprovidecriticallyimportantinformationthatmaybeeither
diagnostic,asinthelevelsofcardiacenzymes,orfacilitatetheaccurate
monitoringofconditionssuchassystemicinflammationorhepaticfail-
ure.Althoughmanyofthesetestsmaybeinterpretedinisolation,itis
usuallyimportanttoexamineany‘trends’thatareevident,e.g.deterio-
rationinrenalfunction,overallcontrolofdiabetesmellitus.
Itisimperative to realisethattheuseofsimple clinical acumenand
skillisacriticallyimportantfacetofpatientcare.Itisalwaysinadequate
toinvestigateapatientbysimply‘orderingafewtests’.Althoughthere
is unquestionably a role for routine screening tests in certain patient
populations,itisusefultorequestandinterpretpertinentinvestigations
in the clinical context of the individual patient. Indeed, significant
errors in clinical management may ensue if data derived from labora-
toryinvestigationsareacteduponwithoutanadequateclinicalassess-
mentofthepatient.
Junior clinical staff are typically the first point of contact for ward
staff who are concerned about the condition of inpatients during the
night or at the weekend. Often, junior doctors will be required to
assess and treat patients ‘out of hours’, despite the fact that they
may not be directly involved in their routine medical care. The key
tosuccessinthesecircumstancesis:
1. Gettogripswiththeacuteproblem,pertinentmedicalbackground
andcurrentdrugtreatment.
2. Examinethepatientbrieflywithparticularemphasisupontherel-
evantphysiological system.
3. If the diagnosis is not apparent then make a differential diagnosis
andinstituteteststhatwillenableyoutomakeadefinitivediagno-
sis.Thismayincludeclinicalchemistry,haematological,radiologi-
calandcardiological investigations.
4. Reconsider the clinical situation when the results ofinvestigations
becomeavailableandintegratealloftheavailabledata.Itmaywell
benecessarytoinstitute appropriatetherapyatthis point.
