C-Reactive Protein: New ApplicationsDr Job Ubbink, D.Sc (Pret), MRCPath (Lond)Consultant: Chemical Pathology

Presentation Outline

• Physiological function of CRP• CRP and ESR: Applications in Rheumatoid

Arthritis• High sensitivity CRP measurements in chronic

disease risk assessment– Coronary heart disease

– Rheumatoid Arthritis

• Serum Amyloid A: New inflammatory marker

CRP: Physiological Function

• Structure• Binds to repeating bacterial polysaccharides and

activates classical complement pathway.• C4 and C3 fragments deposit on bacteria• Adherence and phagocytosis by leucocytes

Presentation Outline

• Physiological function of CRP• CRP and ESR: Applications in Rheumatoid

Arthritis• High sensitivity CRP measurements in chronic

disease risk assessment– Coronary heart disease

– Rheumathoid Arthritis

• Serum Amyloid A: New inflammatory marker

CRP and Rheumatoid Arthritis

• CRP used to:– Establish if inflammation is present

– Monitor course of disease in patients with a known disease process

• New suggested applications:– Determine risk of future disease

CRP: A fundamental role in RA?

• Complement activation• CRP binds also to:

– Phosphatidylcholine

– Chromatin

– Small nuclear RNP particles

• Scavenger function: cutaneous lesions• Detrimental in ischaemia or autoimmunity?

CRP vs ESR

• ESR– Non-specific index of inflammation primarily reflecting

the concentration of fibrinogen and immunoglobulins in plasma

• CRP– Acute phase protein

CRP vs ESR

• ESR used in– Disease Activity Score (DAS)

(DAS = 0.54 (RI)½ + 0.065(swollen joint count) + 0.33 (lognESR) + 0.024)

– American College of Rheumatology 20% improvement score

• CRP considered equally acceptable by ACR• Nomogram relating CRP to ESR

Paulus et al: J Rheumatol; 1999: 26: p2324-31

CRP vs ESR

Paulus et al: J Rheumatol; 1999: 26: p2324-31

CRP vs ESR: Septic arthritis

0

20

40

60

80

100

120

2 3 5 7 9 10 12 14 17 19 23 29

Days

CRP (mg/L)ESR (mm/h)

Data from: Kallio et al: Ped. Inf. Disease J. 1997; 16: 411-13

CRP vs ESR: RA

Study Outline– Arthritis Centre: Kansas – Retrospective study

– Demographic, clinical ESR, CRP, other protein measurements on 774 patients with RA.

– Stepwise multiple regression to determine relationships between variables

F Wolfe: J Rheumatol 1997; 24: 1477-85

CRP vs ESR: RA• Results

– CRP and ESR correlated: r = 0.60

– Relation to other serum proteins:

F Wolfe: J Rheumatol 1997; 24: 1477-85

ProteinProtein % Variation % Variation explained: CRPexplained: CRP

% Variation % Variation explained: ESRexplained: ESR

IgAIgA 1.11.1 9.79.7

IgGIgG 0.60.6 7.37.3

IgMIgM 0.30.3 3.13.1

RFRF 1.21.2 7.77.7

CRP vs ESR: RA• Results

– CRP and ESR correlated: r = 0.60

– Relation to clinical parameters:

F Wolfe: J Rheumatol 1997; 24: 1477-85

ParameterParameter % Variation % Variation explained: CRPexplained: CRP

% Variation % Variation explained: ESRexplained: ESR

Disease ActivityDisease Activity 11.111.1 9.89.8

Grip strengthGrip strength 9.29.2 6.56.5

Joint CountJoint Count 7.87.8 4.84.8

DepressionDepression 4.14.1 2.82.8

CRP vs ESR: RA

• Conclusion– Acute phase is better monitored by CRP– ESR measures acute phase less well, but also

measures elements of chronicity and severity that is not measured by CRP.

F Wolfe: J Rheumatol 1997; 24: 1477-85

Presentation Outline

• Physiological function of CRP• CRP and ESR: Applications in Rheumatoid

Arthritis• High sensitivity CRP measurements in chronic

disease risk assessment– Coronary heart disease

– Rheumathoid Arthritis

• Serum Amyloid A: New inflammatory marker

CRP vs hs-CRP

• Standard CRP tests measure serum CRP concentrations reliably > 10 μg/L

• Hs-CRP measure CRP reliably within the normal range

Presentation Outline

• Physiological function of CRP• CRP and ESR: Applications in Rheumatoid

Arthritis• High sensitivity CRP measurements in chronic

disease risk assessment– Coronary heart disease

– Rheumatoid Arthritis

• Serum Amyloid A: New inflammatory marker

hsCRP: Predictive role in RA?

Background– Clinical rheumatoid arthritis is preceded by an

immunological process

– Rheumatoid factor and other marker antibodies of RA appear in serum before clinical symptoms develop

– Serum CRP: possible inflammatory component in the pre-rheumatoid process?

– Investigated by: Aho et al, J Rheumatol 2000; 27: 1136-1138

hsCRP: Predictive role in RA?

Study Outline– Case control study nested within a Finnish cohort of 19 072

adults

– Baseline examination: 1973 – 1977

– Serum stored at -20○C

– By 1989, 124 individuals had developed RA

– Three controls, matched for age, sex and municipality, were selected for each case

– CRP measured by sensitive immunoassay

Aho et al: J Rheumatol 2000; 27: 1136 - 8

hsCRP: Predictive role in RA?

Results

Aho et al: J Rheumatol 2000; 27: 1136 - 8

QuintileQuintile Cases (n)Cases (n) Controls (n)Controls (n) Odds RatioOdds Ratio 95% CI95% CI

11 2525 7474 1.001.00

22 2121 6969 0.890.89 0.45-1.760.45-1.76

33 3030 7878 1.111.11 0.59-2.080.59-2.08

44 2424 7070 0.990.99 0.51-1.910.51-1.91

55 2424 7474 0.940.94 0.49-1.870.49-1.87

hsCRP: Predictive role in RA?

Comments– Mean time period between sampling and clinical expression

of disease: 5y.

– Putative asymptomatic synovitis preceding clinical disease too mild to be reflected in CRP? (authors)

– Short duration of pre-clinical phase? (authors)

– Sample storage conditions inappropriate? (Ubbink)

– Type 2 statistical error due to inadequate sample sizes? (Ubbink)

Aho et al: J Rheumatol 2000; 27: 1136 - 8

Hs CRP: Clinical Utility

‘A single plasma CRP estimation in an individual subject has a high risk of misclassification and cannot accurately determine whether they are at future risk of atherosclerotic events”

Campbell et al: Ann Clin Biochem 2002; 39: 85 -88

Intra-individual variation of CRP

Intra-individual variation of hsCRP(Healthy individuals followed for 6 months)

De Maat et al: Arterioscler. Thromb. Vasc. Biol. 1996; 16: 1156-62

Intra-individual variation of hsCRP(Stable angina pectoris patients followed for 6 months)

Hs CRP: Clinical Utility

‘In order to reduce the intra-individual variation sufficiently, each subject is likely to require blood samples collected on at least 10 occasions”

Campbell et al: Ann Clin Biochem 2002; 39: 85 -88

Hs CRP: Clinical Utility

‘The task for researchers will be to find another marker for the same, presumably inflammatory, processes that are causing plasma CRP to be elevated. This marker must be capable of being measured with adequate analytical precision and should not have the large intra-individual variation as shown by plasma CRP.”

Campbell et al: Ann Clin Biochem 2002; 39: 85 -88

Presentation Outline

• Physiological function of CRP• CRP and ESR: Applications in Rheumatoid

Arthritis• High sensitivity CRP measurements in chronic

disease risk assessment– Coronary heart disease

– Rheumatoid Arthritis

• Serum Amyloid A: New inflammatory marker

Serum Amyloid A: Inflammatory marker to replace CRP?

• 2 acute phase SAA genes in humans (SAA1, SAA2)

• SAA normally carried as part of HDL-3• Circulating precursor of amyloid deposits in

secondary amyloidosis• Studies suggest that SAA is a more sensitive

marker of disease activity

SAA in assessment of early inflammatory arthritis

G Cunnane et al: J Rheumatol 2000; 27:58-63

SAA in assessment of early inflammatory arthritis

Measure of Measure of disease activitydisease activity

Variation (%) in clinical expression explained by:Variation (%) in clinical expression explained by:

SAASAA CRPCRP ESRESR

Ritchie IndexRitchie Index 21.121.1 10.910.9 4.04.0

Swollen joint Swollen joint countcount

17.617.6 11.611.6 4.04.0

G Cunnane et al: J Rheumatol 2000; 27:58-63

SAA in assessment of early inflammatory arthritis

“Although SAA is a nonspecific marker of inflammation and must be interpreted in the context of the full clinical picture, our observations suggest that an early diagnosis of RA may be made in patients presenting with synovitis and very high SAA levels”

G Cunnane et al: J Rheumatol 2000; 27:58-63

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