Laboratory results: normal ranges
At present ganfyd has very little specific data on the reference ranges or normal values for particular tests, nor any links to sites with such information. Indeed you are well advised to ask your own local laboratory providing the analysis for guidance. However the so called normal range may not be anything of the kind. It may well be a confidence interval or the more standard mean ±(2 x standard deviation) as well as occasionally the range found in medical students or laboratory co-workers assumed to be normal.
If you want to understand the science behind reference ranges see interpreting test results. This page is for more subjective discussion.
From birth to 2 months there is a fall in erythrocyte count and a rapid loss of fetal haemoglobin. Erythrocyte count gradually increases to about 2 years and then stays stable until about 8 years until a rapid increase to about age 15 where values settle to adult values with a sex difference. As shown in the figure, there is a fall in haemoglobin concentration to a minimum about age 6 months and an increase as adolescence sets in, with increasingly marked male and female differences. There is minimum change in haemoglobin in healthy men and women after menstruation ceases. Haemoglobin concentration in capillary (cutaneous) blood is greater than venous blood.
Delaying tying the umbilical cord until after placental expulsion increases a neonate's Hb by about 2.6g/dl. Haemoglobin concentration normally falls in pregnancy but anaemia is important to treat in pregnancy!
Reticulocyte count falls from birth to a low at about 2 weeks, increases to about 4 months then falls through life. There is a sex difference.
The variations with white blood cells in the blood with age are even more complex. At birth there is a high neutrophil count, typically in the range 15 to 45 X 109/l which falls rapidly in first 2 days. Absolute lymphocyte count exceeds the neutrophil count from about 6 weeks to 4 years. Monocyte absolute count steadily decreases with age until the teens. Eosinophils have a day time variation with maximum about midnight and two minima in early morning and late afternoon, and a perhaps not unexpected seasonal fluctuation or with menstrual cycle (maximum at menstruation, minimum at ovulation). Black Africans have lower white cell counts as their leucocytes tend to marginate more than Causacian races.
- ↑ Bain B, Seed M, Godsland I. Normal values for peripheral blood white cell counts in women of four different ethnic origins. Journal of clinical pathology. 1984 Feb; 37(2):188-93.
- ↑ Bain BJ. Ethnic and sex differences in the total and differential white cell count and platelet count. Journal of clinical pathology. 1996 Aug; 49(8):664-6.
Regrettably different manufacturers often have varying specifications for both equipment and analytical methods. This may be due to requirements or practice in a country where the assay was developed and can extend to the problematical area of intellectual property rights meaning that cross validation is difficult. Sometimes there can be clinically significant variation in the range of results reported, both within the so called normal range but also relevant to the interpretation of abnormal results. While most would agree that common reference ranges set for specific tests so far as is practicable would be good practice, we are still far from this ideal. Hopefully the laboratory near you is working to at least BS EN ISO 15189 Medical laboratories. Particular requirements for quality and competence, the present international standard through something similar to CPA (Clinical Pathology Accreditation (UK) Ltd) accreditation in the UK.
- Dartford and Gravesham's Chemical Pathology Handbook which has reference ranges relevant to practice in most if not all the UK
- Leeds Hospitals Biochemistry information including reference ranges
Typical Reference Ranges
Even in this table of common reference ranges which many practicing doctors effectively know by heart you might recognise some issues such as creatinine is such a strong function of age and other variables that its interpretation is best done by other means and that a potassium level in the normal reference range could be toxic for someone with digoxin levels at the higher end of its normal therapeutic range.
|Assay||Venous blood reference range||Comment|
|Sodium (Na+)||135-148 mmol/l||Levels down to 130mmol/l likely to clinically insignificant, levels above 150 mmol/l more likely to be significant|
|Potassium (K+)||3.5 - 5.0 mmol/l||With diuretics (potassium losing/sparing respectively) many function well with levels down to 3.0 and up to 5.5 mmol/l but cardiotoxicity tends to occur just outside this range, or even within this range if patient on drugs or has other electrolyte disturbance|
|Creatinine||- µmol/l||use eGFR !|
|Albumin||35-55 g/l||Also look at total protein !|
|Total Bilirubin||3-20 µmol/l|
|Alanine aminotransferase||0-45 IU/l|
|Aspartate aminotransferase||0-50 IU/l|
|Alkaline phosphatase||90-300 IU/l||Main origins bone and liver|
Interpretation of blood test results
|HBsAg||Active Hepatitis B infection. Detectable during incubation period, acute hepatitis and chronic carrier state. Patient is considered infectious. Persistence beyond 6 months indicates chronic infection.|
|Anti-HBs||Marker of recovery and immunity. Detectable 1-3 months after HBsAg disappears. In the absence of anti-HBc, indicates immunisation with HBV vaccine or passively acquired antibody via hepatitis B immune globulin.|
|Anti-HBc IgM||Consistent with current or recent HBV infection. Antibody may persist 4-6 months after acute stage. Occasionally present in chronic active hepatitis. Routinely performed on HBsAg positive samples|
|Anti-HBc||Detects both IgG and IgM. Indicates current or past HBV infection. May be present during the “window” period when HBsAg has disappeared, but anti-HBs is not yet detectable. May persist longer than anti-HBs and be the only marker for past HBV infection. Not associated with recovery or immunity.|
|HBeAg||Suggestive of high degree of infectivity. Persistence beyond 10 weeks suggests chronic liver disease.|
|Anti-HBe||Anti-HBe appears prior to loss of HBsAg and signals reduced level of infectious virus. Suggests early convalescence or past infection with HBV, but may also be seen in HBV chronic carrier state|
|Interpretation||HBsAg||Anti-HBcIgM||Hbe Ag||Anti- HBe||Anti-HBc||Anti-HBs|
|No evidence of HBV infection||neg||neg||neg||neg||neg||neg|
|Acute HBV infection||pos||pos||pos||pos||pos||neg|
|Recent HBV infection – early convalescence||neg||pos||neg||pos||neg|
|Previous HBV infection||neg||neg||neg||pos/neg||pos||pos|
|HBV vaccine response||neg||neg||neg||pos||neg||pos|
|Chronic HBV (if HBsAg pos for > 6 months) - low infectivity||pos||neg||neg||pos||pos||neg|
|Chronic HBV (if HBsAg pos for > 6 months) - intermediate infectivity||pos||neg||neg||neg||pos||neg|
|Chronic HBV (if HBsAg pos for > 6 months) - high infectivity||pos||neg||pos||neg||pos||neg|
This article is a work in progress. Please feel free to contribute to it.