<prompt> Diagnosis of folic acid deficiency is done by all exceptFIGLU estimationPeripheral blood smearsAICAR estimationtransketolase activity  <response>: Blood Level: Normal folic acid level in serum is about 20 nanogramsml and about 200 microgramml of packed cells. The level is measured by radioimmunoassay. Histidine load test or FIGLU excretion test: Histidine is normally metabolised to formimino glutamic acid FIGLU from which formimino group is removed by THFA. Therefore in folate deficiency, FIGLU is excreted in the urine. AICAR excretion: In the purine nucleotide synthesis, the last step is the addition of C2 with the help of N10-formyl THFA, the precursor, aminoimidazole carboxamide ribosyl-5-phosphate AICAR accumulates and is excreted in the urine. Peripheral blood picture. Ref: DM Vasudevan - Textbook of Biochemistry, 8th edition, page no: 475, 297 