Sample stability:
|
Serum
|
EDTA
|
Units: mg/L
Reference ranges:
|
age < 3 months |
0 - 10 |
|
age: 3 months to 15 years |
0 - 8 |
|
adults |
0 - 5 |
Uncertainty of Measurement : 0.2 mg/L at a concentration of 1.4 mg/L, 7% at concentrations of 4 mg/L and higher.
Principle: Immunoturbidometric assay
Reagents: Roche Tina-quant C-Reactive Protein IV
Analyser: Cobas c702
CRP is a protein produced by the liver. Its production is regulated by cytokines. The plasma CRP level also is partly genetically determined.
CRP as a marker of inflammation
In unwell patients CRP is useful as a marker of severity of inflammation (for example infections, autoimmune diseases, trauma and malignancies).
In almost all clinical settings it is a more sensitive and specific marker than ESR. It also follows the time course of inflammation more closely, with rise within 4-8 hr of tissue damage and more rapid fall on resolution (half-life about 19 hr). It is also not affected by other factors such as high fibrinogen (pregnancy), haematocrit, or monoclonal bands.
Monitoring of the acute phase response should be done at an interval of at least 24 hours between CRP tests, to observe a significant change in results.
ESR, however, is preferred over CRP in the following conditions:
- SLE and variants
- Rheumatoid arthritis
- Other connective tissue diseases including ankylosing spondylitis, reactive arthritis, Sjogren's syndrome, systemic sclerosis, antiphospholipid syndrome
- Acute rheumatic fever and endocarditis monitoring
Usually only ESR or CRP is required. There is no need to request both. The only known evidence-based exception is for assessment of periprosthetic joint infections of the hip and knee (Guideline published by the American Academy of Orthopaedic Surgeons in 2010, which recommended both ESR and CRP).
CRP as a cardiovascular risk marker
In well patients CRP has some utility as a CVD risk marker. In this context it is called high sensitivity or hsCRP as t he levels measured are usually below 5mg/L.
At LabPlus the CRP assay can measure down to 0.6 mg/L: results lower than this are reported as "less than 0.6 mg/L".
Recent guideline documents recommend use of hsCRP currently for cardiovascular risk assessment only in patients where it will influence evidence-based treatment decisions , e.g. those who fall near the threshold for drug treatment. Measurement is not recommended for:
- routine CVD risk screening of the general population
- for those already known to be at high risk, or
- for monitoring
As an example, the Canadian guidelines suggest it may be helpful in certain patients at intermediate (10-19% five year) risk, specifically men >50yr and women >60yr with LDL <3.5 mmol/L. In this group, patients with a CRP level >2mg/L have been shown to benefit from statin therapy (Jupiter trial).
NZGG Guidelines see
http://www.nzgg.org.nz/guidelines/0035/CVD_Risk_Full.pdf keyword "CRP")
Canadian Guidelines see
Drug Interference by carboxypenicillins
Ticarcillin (Claventin) and probably other carboxypenicillins cause negative interference in the CRP assay (Roche) used at Labplus. This may cause falsely low CRP results.
Associate Professor Rohan Ameratunga , Immunopathologist: Ext 22106 Locator 93-5724
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427