A<unk> <unk> 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<unk> . Plasma or whole<unk>  In this article, all values (except the ones listed below) denote<unk>  plasma concentration, which is approximately 60–100% larger than the actual<unk>  concentration if the amount inside red<unk>  cells (RBCs) is negligible. The precise factor depends on hematocrit as well as amount inside RBCs. Exceptions are mainly those values that denote total<unk>  concentration, and in this article they are: * All values in Hematology – red<unk>  cells (except hemoglobin in plasma) * All values in Hematology – white<unk>  cells * Platelet count (Plt) A few values are for inside red<unk>  cells only: * Vitamin B9 (folic acid/folate) in red<unk>  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<unk>  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<unk> <unk> for a<unk> <unk> is generally the venous<unk>  as the standard process of obtaining a sample is by venipuncture. An exception is for acid–base and<unk>  gases, which are generally given for arterial<unk> . Still, the<unk>  values are approximately equal between the arterial and venous sides for most substances, with the exception of acid–base,<unk>  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<unk><unk>  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<unk>  In contrast, optimal (health)<unk> or therapeutic target is a<unk> <unk> 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<unk>  lipids, so these tables give limits on both standard and optimal (or target)<unk> . 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<unk> s<unk> may vary with age, sex, race, pregnancy, diet, use of prescribed or herbal drugs and stress.<unk><unk>  often depend on the analytical method used, for reasons such as inaccuracy, lack of standardisation, lack of certified<unk>  material and differing antibody reactivity. Also,<unk><unk>  may be inaccurate when the<unk>  groups used to establish the<unk>  are small.
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