Reference ranges for blood tests

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:

A few values are for inside red blood cells only:

Units

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 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.

By units

Units don't 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.

Ions and trace metals

Included here are also related binding proteins, like ferritin and transferrin for iron, and ceruloplasmin for copper.

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.

Sex hormones

The diagrams below take inter-cycle and inter-woman variability into account in displaying reference ranges for estradiol, progesterone, FSH and LH.

Vitamins

Also including the vitamin B₁₂)-related amino acid homocysteine.

Red blood cells

These values (except Hemoglobin in plasma) are for total blood and not only blood plasma.

White blood cells

These values are for total blood and not only blood plasma.

Acute phase proteins

Acute phase proteins are markers of inflammation.

Autoantibodies

Autoantibodies are usually absent or very low, so instead of being given in standard reference ranges, the values usually denote where they are said to be present, or whether the test is a positive test. There may also be an equivocal interval, where it is uncertain whether there is a significantly increased level. All included values are given for the ELISA test.

Other electrolytes and metabolites

Electrolytes and Metabolites: For iron and copper, some related proteins are also included.