Cyanosis and infants

  4 month old baby boy has developed cyanotic hands and feet almost continously.  Otherwise, has been relatively healthy.  Was born to 17 year old, diabetic ( has been on insulin since age 7 )teen.
  What should be considered and ruled out?  
  What objective testing is usually performed?
  Any other commentaries would be most appreciated! ( IE - Suggestions of questions to pose to consulting pediatric cardiologist - treating physician arranged evaluation ).
  Thank you.
Dear Mary:
Cyanosis means that a substantial portion of the oxygen-carrying
protein in the blood, hemoglobin, is not carrying the oxygen
for which it is designed (it is thus unsaturated). Cyanosis is
fruitfully divided into two types, central and peripheral. Central
cyanosis (of the tongue and mucous membranes) usually reflects
decreased saturation of the hemoglobin in arterial blood, most often
resulting from heart or lung disease, or, less commonly, from an
increased amount of abnormal hemoglobin. Peripheral cyanosis, which
is confined to the extremities, as seems likely in the four-month-old
baby described in your letter, reflects an increased difference in the
saturation of hemoglobin between arterial and venous blood at a time when
arterial hemoglobin saturation is normal. This occurs when blood vessels
in the hands and feet constrict and slow the flow of blood, permitting
more oxygen than usual to be extracted from hemoglobin by the surrounding
tissues, thus desaturating it.
Central cyanosis can be obvious clinically or may require the
determination of hemoglobin oxygen saturation by pulse oximetry. This
is a simple test, readily available in most primary care offices.
If necessary to sort out the problem, a primary care physician can
also determine the number of hemoglobin-carrying red blood cells by
another simple test. Neither test requires a visit to a cardiologist.
If central cyanosis is ruled out, peripheral cyanosis must be present.  
Peripheral (or acrocyanosis) is expected and therefore normal in
newborn infants. It is also common (and normal) in young infants
whenever they become cold. Occasionally older children, adolescents,
and adults develop a pathological constriction of blood vessels in
the fingers and toes in response to cold or emotional stress
(Raynaud's disease) or in response to connective tissue or blood
disorders (Raynaud's phenomenon). This is more likely to occur
among females.
If the four-month-old baby is feeding easily, growing normally,
and is free of other symptoms, heart or lung disease would be
exceedingly unlikely. Raynaud's disease or phenomenon would be
extraordinary in a healthy infant. Careful observations and a
very few simple tests should sort the matter out promptly.
I hope this is useful to you. This information is offered for
educational purposes only. Your child's physician has the responsibility
to work with you to assure the best possible outcome for the infant.
If you would like further assistance from the Henry Ford Health System,
please call [phone]
HFHS M.D.-HSW