More specifically, according to a 2014 UK guideline,
A serum folate level of less than 7 nmol/L (3 μg/L) is indicative of folate deficiency;
Red blood cell folate testing is not routinely performed, since serum folate is sufficient in most cases, however, if there is a strong suspicion of folate deficiency despite a normal serum folate level, a red cell folate test may be performed. Plasma total homocysteine is only measured in special circumstances. A level above 15 μmol/L could be indicative of a folate deficiency, but local reference ranges should be taken into account. Prevention and treatment
Diet
Folate is acquired in the diet by the consumption of leafy green vegetables, legumes and organ meats. When cooking, use of steaming, a food steamer, or a microwave oven can help keep more folate content in the cooked foods. Supplementation
Folic acid is a synthetic derivative of folate and is acquired by dietary supplementation. Multi-vitamin dietary supplements contain folic acid as well as other B vitamins. Non-prescription folic acid is available as a dietary supplement in some countries, and some countries require the fortification of wheat flour, corn meal or rice with folic acid with the intention of promoting public health through increasing blood folate levels in the population. Fortification
After the discovery of the link between insufficient folic acid and neural tube defects, governments and health organizations worldwide made recommendations concerning folic acid supplementation for women intending to become pregnant.
Tick-borne diseases like Rocky Mountain spotted fever produce a rash that may become extensive enough so as to be classified as exanthemous in as many as 90% of children with the disease. See also
List of cutaneous conditions

References
External links

Overview at About.com
Definition at MedTerms
Differential diagnosis
Dermatology Quiz Includes photo, diagnosis, and treatment of unilateral laterothoracic exanthem (ULE).