A reduced concentration of calcitriol in the blood. Calcitriol is also known as 1,25-dihydroxycholecalciferol or 1,25-dihydroxyvitamin D3. The phenotype is Human Phenotype Ontology identifier HP_0012052 (Low serum calcitriol). Also known as: Low serum 1,25-dihydroxycholecalciferol, Low serum 1,25-dihydroxyvitamin D3.