MCC and nutritional biotin deficiency: ,216 Indicators of biotin deficiency include low serum and low urinary levels of biotin, high urinary excretion of 3-hydroxyisovaleric acid in relation to creatinine excretion, biotinylated methylcrotonyl-coenzyme A carboxylase (MCC) and propionyl-coenzyme A carboxylase (PCC) in lymphocytes.31