Laboratory results: normal ranges

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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.


Haematology results

Normal haemoglobin concentration peripheral venous blood

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.

Platelet count starts out about 230 X 109/l and steadily increases in childhood to adult values say 150-690 X 109/l with another fall over age 60. In women platelet count falls before menstruation.

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.[1][2]


Biochemistry results

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.

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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.

Typical adult reference ranges for common clinical biochemistry assays in UK
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

Immunology results

Infectious diseases

Hepatitis B

Interpretation of blood test results

Quick reference
Positive Result Interpretation
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
Selected Hepatitis B Serology Interpretations
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.