Laboratory reference values

Published on 29/05/2015 by admin

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Last modified 22/04/2025

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Appendix 4 Laboratory reference values

The reference values and ranges for these blood tests are given in the system of international units (SI) and are based on guidelines from the Royal College of Pathologists of Australasia. They may vary from laboratory to laboratory. When paediatric reference ranges may differ from adult ranges they are indicated by an asterisk (^∗). Further information and resources can be found at the online manual of the Royal College of Pathologists of Australasia at http://www.rcpamanual.edu.au/.

Markers of inflammation: ESR and CRP

Comparison between ESR and CRP

• Both investigations are markers of inflammation and there tends to be a broad correlation between them.

• The CRP levels rise faster than the ESR.

• The levels are similar after 24 hours or so.

• CRP levels fall faster than the ESR.

• CRP levels (unlike ESR) are not affected by pregnancy.

• ESR may be very high with a normal CRP in giant cell arteritis/polymyalgia rheumatica.

• CRP costs more.

Relative values (mm/hour) of typical examples of erythrocyte sedimentation rate (ESR) readings

There is a lag phase of 24–48 hours between the onset of inflammatory stimulation and the production of inflammatory proteins that increase in the ESR. There is also a delay in the fall of the ESR after resolution of the inflammation because the fibrinogen levels can remain elevated for 6 days or so after acute tissue damage—this can take 4–8 weeks to return to normal.

A normal value of < 20 mm/hour generally excludes inflammation. The OCP can push the level to 20–25 mm/hour.

Normal values of ESR—reference interval

Child
	2–15 mm/hour
Adult male
17–50 years	1–10 mm/hour
> 50 years	2–15 mm/hour
Adult female
17–50 years	3–12 mm/hour
> 50 years	5–20 mm/hour

C-reactive protein levels (normal value < 10 mg/L)

MARKED ELEVATION > 40 mg/L	NORMAL TO MILD ELEVATION
Bacterial infection Abscess Crohn’s disease Active rheumatic disease: – rheumatic fever Connective tissue disorders: – rheumatoid arthritis – vasculitis Malignant disease Trauma/tissue injury

Viral infection

Ulcerative colitis

Atherosclerosis

Steroid/oestrogen therapy

Interpretation of iron studies

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