Clinical biochemistry/normal values

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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
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