Reference ranges (reference intervals) for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemistry (also known as "clinical biochemistry", "chemical pathology" or "pure blood chemistry"), the area of pathology that is generally concerned with analysis of bodily fluids.
Blood test results should always be interpreted using the reference range provided by the laboratory that performed the test.
Interpretation A reference range is usually defined as the set of values 95 percent of the normal population falls within (that is, 95% prediction interval). It is determined by collecting data from vast numbers of laboratory tests.
Plasma or whole blood In this article, all values (except the ones listed below) denote blood plasma concentration, which is approximately 60–100% larger than the actual blood concentration if the amount inside red blood cells (RBCs) is negligible. The precise factor depends on hematocrit as well as amount inside RBCs. Exceptions are mainly those values that denote total blood concentration, and in this article they are: All values in Hematology – red blood cells (except hemoglobin in plasma) All values in Hematology – white blood cells Platelet count (Plt) A few values are for inside red blood cells only: Vitamin B9 (folic acid/folate) in red blood cells Mean corpuscular hemoglobin concentration (MCHC)
Units Mass concentration (g/dL or g/L) is the most common measurement unit in the United States. Is usually given with dL (decilitres) as the denominator in the United States, and usually with L (litres) in, for example, Sweden. Molar concentration (mol/L) is used to a higher degree in most of the rest of the world, including the United Kingdom and other parts of Europe and Australia and New Zealand. International units (IU) are based on measured biological activity or effect, or for some substances, a specified equivalent mass. Enzyme activity (kat) is commonly used for e.g. liver function tests like AST, ALT, LD and γ-GT in Sweden. Percentages and time-dependent units (mol/s) are used for calculated derived parameters, e.g. for beta cell function in homeostasis model assessment or thyroid's secretory capacity.
Arterial or venous If not otherwise specified, a reference range for a blood test is generally the venous range, as the standard process of obtaining a sample is by venipuncture. An exception is for acid–base and blood gases, which are generally given for arterial blood.
Still, the blood values are approximately equal between the arterial and venous sides for most substances, with the exception of acid–base, blood gases and drugs (used in therapeutic drug monitoring (TDM) assays). Arterial levels for drugs are generally higher than venous levels because of extraction while passing through tissues.
Usual or optimal Reference ranges are usually given as what are the usual (or normal) values found in the population, more specifically the prediction interval that 95% of the population fall into. This may also be called standard range. In contrast, optimal (health) range or therapeutic target is a reference range or limit that is based on concentrations or levels that are associated with optimal health or minimal risk of related complications and diseases. For most substances presented, the optimal levels are the ones normally found in the population as well. More specifically, optimal levels are generally close to a central tendency of the values found in the population. However, usual and optimal levels may differ substantially, most notably among vitamins and blood lipids, so these tables give limits on both standard and optimal (or target) ranges. In addition, some values, including troponin I and brain natriuretic peptide, are given as the estimated appropriate cutoffs to distinguish healthy people from people with specific conditions, which here are myocardial infarction and congestive heart failure, respectively, for the aforementioned substances.
Variability
References range may vary with age, sex, race, pregnancy, diet, use of prescribed or herbal drugs and stress. Reference ranges often depend on the analytical method used, for reasons such as inaccuracy, lack of standardisation, lack of certified reference material and differing antibody reactivity. Also, reference ranges may be inaccurate when the reference groups used to establish the ranges are small.
Sorted by concentration
By mass and molarity Smaller, narrower boxes indicate a more tight homeostatic regulation when measured as standard "usual" reference range.
Hormones predominate at the left part of the scale, shown with a red at ng/L or pmol/L, being in very low concentration. There appears to be the greatest cluster of substances in the yellow part (μg/L or nmol/L), becoming sparser in the green part (mg/L or μmol/L). However, there is another cluster containing many metabolic substances like cholesterol and glucose at the limit with the blue part (g/L or mmol/L).
The unit conversions of substance concentrations from the molar to the mass concentration scale above are made as follows: Numerically:
Measured directly in distance on the scales: , where distance is the direct (not logarithmic) distance in number of decades or "octaves" to the right the mass concentration is found. To translate from mass to molar concentration, the dividend (molar mass and the divisor (1000) in the division change places, or, alternatively, distance to right is changed to distance to left. Substances with a molar mass around 1000g/mol (e.g. thyroxine) are almost vertically aligned in the mass and molar images. Adrenocorticotropic hormone, on the other hand, with a molar mass of 4540,PROOPIOMELANOCORTIN; NCBI / POMC Retrieved on September 28, 2009 is 0.7 decades to the right in the mass image. Substances with molar mass below 1000g/mol (e.g. electrolytes and metabolites) would have "negative" distance, that is, masses deviating to the left. Many substances given in mass concentration are not given in molar amount because they haven't been added to the article.
The diagram above can also be used as an alternative way to convert any substance concentration (not only the normal or optimal ones) from molar to mass units and vice versa for those substances appearing in both scales, by measuring how much they are horizontally displaced from one another (representing the molar mass for that substance), and using the same distance from the concentration to be converted to determine the equivalent concentration in terms of the other unit. For example, on a certain monitor, the horizontal distance between the upper limits for parathyroid hormone in pmol/L and pg/mL may be 7 cm, with the mass concentration to the right. A molar concentration of, for example, 5 pmol/L would therefore correspond to a mass concentration located 7 cm to the right in the mass diagram, that is, approximately 45 pg/mL.
By units Units do not necessarily imply anything about molarity or mass.
A few substances are below this main interval, e.g. thyroid stimulating hormone, being measured in mU/L, or above, like rheumatoid factor and CA19-9, being measured in U/mL.
By enzyme activity
White blood cells
Sorted by category
Ions and trace metals
Included here are also related binding proteins, like ferritin and transferrin for iron, and ceruloplasmin for copper.
Test Lower limit Upper limit Unit* Comments Sodium (Na) 135, 137 145, 147 mmol/L or mEq/L See hyponatremia or hypernatremia 310,Derived from molar values using molar mass of 22.99 g•mol−1 320 330, 340 mg/dL Potassium (K) 3.5, 3.6 5.0, 5.1 mmol/L or mEq/L See hypokalemia or hyperkalemia 14Derived from molar values using molar mass of 39.10 g•mol−1 20 mg/dL Chloride (Cl) 95, 98, 100 105, 106, 110 mmol/L or mEq/L See hypochloremia or hyperchloremia 340Derived from molar values using molar mass of 35.45 g•mol−1 370 mg/dL Ionized calcium (Ca) 1.03, 1.10 1.23, 1.30 mmol/L See hypocalcaemia or hypercalcaemia 4.1,Derived from molar values using molar mass of 40.08 g•mol−1 4.4 4.9, 5.2 mg/dL Total calcium (Ca) 2.1,Derived from mass values using molar mass of 40.08 g•mol−1 2.2 2.5, 2.6, 2.8 mmol/L 8.4, 8.5 10.2, 10.5 mg/dL Total serum iron (TSI) – male 65, 76 176, 198 μg/dL See hypoferremia or the following: iron overload (hemochromatosis), iron poisoning, siderosis, hemosiderosis, hyperferremia 11.6,Diagnostic Chemicals Limited > Serum Iron-SL Assay July 15, 2005 13.6 30, 32, 35 μmol/L Total serum iron (TSI) – female 26, 50 170 μg/dL 4.6, 8.9 30.4 μmol/L Total serum iron (TSI) – newborns 100 250 μg/dL 18Derived from mass values using molar mass of 55.85 g•mol−1 45 μmol/L Total serum iron (TSI) – children 50 120 μg/dL 9 21 μmol/L Total iron-binding capacity (TIBC) 240, 262 450, 474 μg/dL 43, 47 81, 85 μmol/L Transferrin 190,Table 1. Page 133" Clinical Chemistry 45, No. 1, 1999 (stating 1.9–3.3 g/L) 194, 204 326, 330, 360 mg/dL 25Derived by dividing mass values with molar mass 45 μmol/L Transferrin saturation 20 50 % Ferritin – Males and postmenopausal females 12Ferritin by: Mark Levin, MD, Hematologist and Oncologist, Newark, NJ. Review provided by VeriMed Healthcare Network 300 Updated: Jan 02, 2016 ng/mL or μg/L 27Derived from mass values using molar mass of 450,000 g•mol−1 670 pmol/L Ferritin – premenopausal females 12 150 – 200 ng/mL or μg/L 27 330 – 440 pmol/L Ammonia 10, 20 35, 65 μmol/L See hypoammonemia and hyperammonemia 17,Derived from molar values using molar mass of 17.03 g/mol 34 60, 110 μg/dL Copper (Cu) 70 150 μg/dL See hypocupremia or hypercupremia 11Derived from mass values using molar mass of 63.55 g•mol−1 24 μmol/L Ceruloplasmin 15 60 mg/dL 1Derived from mass using molar mass of 151kDa 4 μmol/L Phosphate (HPO42−) 0.8 1.5 mmol/L See hypophosphatemia or hyperphosphatemia Inorganic phosphorus (serum) 1.0 1.5 mmol/L 3.0 4.5 mg/dL Zinc (Zn) 60, 72Derived from molar values using molar mass of 65.38 g/mol 110, 130 μg/dL See zinc deficiency or zinc poisoning 9.2,Derived from mass values using molar mass of 65.38 g/mol 11 17, 20 μmol/L Magnesium 1.5, 1.7Derived from molar values using molar mass of 24.31 g/mol 2.0, 2.3 mEq/L or mg/dL See hypomagnesemia or hypermagnesemia 0.6,Derived from mass values using molar mass of 24.31 g/mol 0.7 0.82, 0.95 mmol/L
Note: Although 'mEq' for mass and 'mEq/L' are sometimes used in the United States and elsewhere, they are not part of SI and are now considered redundant.
Acid–base and blood gases
If arterial/venous is not specified for an acid–base or blood gas value, then it generally refers to arterial, and not venous which otherwise is standard for other blood tests.
Acid–base and blood gases are among the few blood constituents that exhibit substantial difference between arterial and venous values. Still, pH, bicarbonate and base excess show a high level of inter-method reliability between arterial and venous tests, so arterial and venous values are roughly equivalent for these.
Test Arterial/Venous Lower limit Upper limit Unit pH Arterial 7.34, 7.35 7.44, 7.45 Venous 7.31The Medical Education Division of the Brookside Associates / ABG (Arterial Blood Gas) Retrieved on Dec 6, 2009 7.41 [H+] Arterial 36 44 nmol/L 3.6Derived from molar values using molar mass of 1.01 g•mol−1 4.4 ng/dL Base excess Arterial & venous −3 +3 mEq/L Oxygen partial pressure (pO2) Arterial pO2 10, 11 13, 14 kPa 75, 83 100, 105 mmHg or torr Venous 4.0 5.3 kPa 30 40 mmHg or torr Oxygen saturation Arterial 94, 95,Merck Manuals > Common Medical Tests > Blood Tests Last full review/revision February 2003 96 100 % Venous Approximately 75 Carbon dioxide partial pressure (pCO2) Arterial PaCO2 4.4, 4.7Derived from mmHg values using 0.133322 kPa/mmHg 5.9, 6.0 kPa 33, 35 44, 45 mmHg or torr Venous 5.5, 6.8 kPa 41 51 mmHg or torr