bronchitis or pneumonia. Typically, viral pneumonias do not result in values above 5 mg/dL Malignant tumors Increasing levels of CRP imply a poor prognosis and frequently suggest metastalic spread. Burns CRP

 

Calculations

1. Interpolate ∆A of the diluted test specimen on the

calibration curve and obtain the RF concentration ‘C’

of the diluted test specimen.

2. Multiply the RF concentration ‘C’ with the dilution

factor (F) of the test specimen for obtaining the

concentration of RF in the neat test specimen.

Concentration of RF in the neat test specimen in IU/mL

= C × F

(where ‘F’ is the dilution factor of the test specimen, i.e.

10 for 1:10 dilution of test specimen and so on).

Specific Performance Characteristics

Measuring Range

The QUANTIA-RF reagent has been designed to measure

RF concentrations in the range 7.5–120 IU/mL and is linear

between the measuring range.

Detection Limit/Analytical Sensitivity

Detection limit: 7.5 IU/mL.

The detection limit represents the lowest measurable

RF concentrations that can be distinguished from zero.

Prozone Limit

No prozone effect was observed up to a concentration of

1250 IU/mL of RF.

Interference

No interference was observed with:

Interference factor No interference up to

Glucose 500 mg/dL

Albumin 10 g/dL

Bilirubin 50 mg/dL

Hemoglobin 500 mg/dL

Triglycerides 1000 mg/dL

Reference Values

The reference values of RF in normal population are <10

IU/mL.

Each laboratory should define its own reference range

for relevant population.

Remarks

1. Usage of well-calibrated equipment and accessories

and procedures is critical for achieving correct

results.

2. When ∆A obtained for the test specimen is greater

than the ∆A of the standard with highest concentration

then, it indicates that the concentration of IgA in the

test specimen is beyond the measuring range of the

QUANTIA-RF assay. Such specimens should be rerun

with further dilutions.

3. Markedly lipemic, hemolyzed, and contaminated

serum samples could produce non-specific values.

4. Use of plasma rather than serum can lead to nonspecific values.

5. Do not read results beyond 4 minutes.

6. Rheumatoid factors are not exclusively found in

rheumatoid arthritis but sometimes in syphilis,

systemic lupus erythromatosus, hepatitis and hypergammaglobulinemia also.

7. It is recommended that results of the tests should be

correlated with clinical findings to arrive at the final

diagnosis.

8. QUANTIA-RF assay is sensitive to the presence of IgM

IgA with heterogenous specificity.

C-REACTIVE PROTEIN

C-Reactive protein (CRP) is an abnormal serum glucoprotein produced by the liver during acute inflammation

or infections. CRP is synthesized by the liver under

regulatory control of cytokines. Interleukins 1b and 6 and

tumor necrosis factors are the most important regulators

of CRP synthesis. The intact CRP molecule is a pentameric

protein with identical subunit arranged in a doughnut

shaped polymer.

The function of CRP is felt to be related to its role in

the innate immune system. Similar to IgG it activates

complement, binds to Fc receptor and acts as an opsonin

for various pathogens. Interaction of CRP with Fc receptors leads to the generation of proinflammatory cytokines

that enhance inflammatory response. Unlike IgG, which

specifically recognize distinct antigenic epitopes, CRP

recognizes altered self and foreign molecules based

on pattern of recognition. This recognition provides an

early defense and leads to a proinflammatory signal and

activation of the humoral immune response. CRP binds to

apoptotic cells, protects the cells from assembly of terminal

complement components and sustains an antiflammatory

innate immune response.

All acute inflammatory process (infectious and noninfectious) and certain malignant conditions result in

rise in serum CRP, as a non-specific phenomenon. CRP

production is a non-specific response to disease and it can

never on its own be used as a diagnostic test. However,

if the CRP results are interpreted in the light of clinical

information on the patient it can provide exceptionally

useful information.

Diagnostic Immunology 721

Levels of CRP increase very rapidly in response to

trauma, inflammation and infection and decrease very

rapidly with the resolution of the condition. An activated

CRP is always associated with pathological changes. Hence,

determination of CRP is of great value in diagnosis, treatment

and monitoring of inflammatory condition. Measurement of

CRP may be helpful to know whether the patient is getting

better, or if there are any complications arising.

CRP Measurements Help in Diagnosis and Management

Rheumatology The rheumatic diseases exhibit joint or soft tissue symptoms such as back pain, and myalgia.

However, such symptoms may also be due to psychogenic factors. The elevation of acute

phase proteins confirms the presence of organic disease but a value within the reference range

does not exclude a mild local disease. In condition like ankylosing spondylitis, serum CRP may

be elevated before the onset of clinical symptoms

Adult rheumatoid arthritis Increased CRP levels are found in more than 90% of adults with this condition and in established

disease, levels relate to severity. Values of up to 5 mg/dL are associated with mild inflammation

and values around 10 mg/dL indicate more severe disease. Certainly CRP levels correlate more

closely with radiologically determined joint damage than other serological test. Typically, if

a patient responds to a particular drug the fall in CRP precedes the improvement in clinical

symptoms by about 6 weeks and the radiological improvement by about 6 months

Ankylosing Spondylitis Back pain is a very common clinical symptom and an elevated CRP is a strong indication of

organic disease such as ankylosing spondylitis

Polymyalgia Rheumatica CRP concentration is markedly raised. If untreated 30% of patients will develop cranial arteritis

with a serious risk of eyesight. CRP rapidly falls to normal as the disease responds to therapy

with corticosteroids

Connective tissue diseases SLE, polymyositis, systemic sclerosis, in these cases acute phase response is minimal even

in active disease. Hence, CRP levels can be used to distinguish these conditions from other

rheumatic diseases

Infections Bacterial infections are associated with some of the highest CRP levels and its measurement is a

sensitive marker for bacterial sepsis. Gram-negative bacteria generally elicit more reproducible

responses than gram-positive bacteria, with modest responses to parasitic infestations and

minor responses to viruses and fungi. CRP measurement is useful in detecting infections

where clinical and microbiological diagnosis is difficult but where infection is suspected. CRP

levels relate to the extent and intensity of sepsis and successful treatment leads to decline in

levels within about 3 days

Pediatric fever In children, although fever is most often due to viral infection, this is difficult to distinguish

from bacterial sepsis such as otitis media, bronchitis, tonsillitis, and cystitis, and antibiotics are

often prescribed unnecessarily. It has been shown that, in children who have been ill for more

than 12 hours, a CRP level of greater than 4 mg/dL had a diagnostic sensitivity of 79%, and a

specificity of 90% for the diagnosis of bacterial infections

Adults postoperative surgery Surgery of all types induces inflammation and an acute phase response roughly in proportion

to the extent of tissue damage. In uncomplicated cases CRP rises above 1 mg/dL by about

6 hours, reaches a peak rarely greater than 15 mg/dL at about 48 hours, and declines

thereafter to baseline values by 7–10 days. Postoperative complications such as infections,

tissue necrosis, hematoma, and thrombosis, depending upon when they occur, will maintain

a raised CRP level after 48 hours, or result in a secondary increase. In many cases the raised

CRP precedes the clinical diagnosis of the complication pathology by up to 24 hours. In such

situations, single values are of little value and serial monitoring is essential

Appendicitis Using a cut off of 1 mg/dL it has been reported that CRP has clinical sensitivity for this condition

of 68.2% and a specificity of 75.1%

Meningitis Some studies using serum CRP have described almost perfect discrimination between bacterial

and viral meningitis in children. Bacterial meningitis is associated with higher CRP levels than

aseptic or viral meningitis. Appropriate therapy for bacterial and tuberculous meningitis causes

fall in CRP levels, and hence, this simple test can be used to monitor response to treatment with

many advantages over repeated lumbar punctures especially in children

Contd...

722 Concise Book of Medical Laboratory Technology: Methods and Interpretations Pulmonary infection Pneumonia can be difficult in the elderly where the febrile response may be lost. A CRP level

above 10 mg/dL provides a very strong indication of bacterial infection such as purulent

bronchitis or pneumonia. Typically, viral pneumonias do not result in values above 5 mg/dL

Malignant tumors Increasing levels of CRP imply a poor prognosis and frequently suggest metastalic spread.

Burns CRP levels increase significantly in patients with extensive burns. A second peak of CRP later

implies superadded infection as a late complication of burns

Myocardial infarctions Peak CRP levels occur about 50 hours after the onset of pain in myocardial infarction, and

correlate well with peak serum levels of cardiac isoenzymes such as CKMB. In patients who

recover uneventfully the CRP levels fall rapidly towards normal. However, complications such

as persistent cardiac dysfuntion further infarction, intercurrent infection, thromboembolism,

are associated with either persistently raised CRP levels or secondary increase after initial

decrease. Angina without infarction does not stimulate CRP production. Routine assays of CRP

in patients with chest pain may thus assist in diagnosis, and management of complications

Immunocompromised Fever in patients with leukemia and neutropenia can be caused by infection, the underlying

patients in acute leukemia disease process, administration of blood products, and cytotoxic therapy.