kolthoff was born on 27 january 1908 in batavia, dutch east indies. she was the only child of father abraham kolthoff (1863-1940) who was director officer of health 1st class of the k.n.i.l. and worked in in batavia. her mother was johanna cornelia brandon (1870-1947). they moved back to the netherlands where she married to mechanical engineer lucas ruinen (1901-1993) on 20 august 1937 in the hague. they had four children together.