The single-band part of the orbital magnetic susceptibility of conduction electrons, which includes a term dependent on the Fermi-liquid interaction function, is obtained on the basis of quantum theory. It is shown that Fermi-liquid interaction has only a small influence on the orbital contribution to anomalies of the susceptibility caused by singularities in the density of states with energies close to Fermi energy, and this contribution can mainly be described by allowing for singularities in the Peierls formula. The relation between the orbital and spin contributions and its anisotropy are discussed for one type of singularity.