Congenital Adrenal Hyperplasia

Congenital Adrenal Hyperplasia can present in childhood, adolescence or adulthood. CAH is an autosomal recessive genetic condition, the most common form being due to 21 hydroxylase deficiency. The diagnosis is confirmed biochemically with elevated 17 hydroxyprogesterone (17OHP) and androgens.

Baseline investigations - all patients

 Full blood count

Useful indicator of general health and underlying disease.

Urea and electrolytes  

Hyponatraemia and hyperkalaemia indicate mineralocorticoid deficiency particularly in the child presenting acutely unwell.

Hypokalaemia may raise the possibility of glucocorticoid excess.

Liver function test  

Useful indicator of general health and underlying disease.

Fatty liver is common in both obesity and diabetes and may be associated with supraphysiologocal glucocorticoid treatment.

Bone profile 

Useful indicator of general health and underlying disease. Hypercalcaemia may be associated with subphysiological glucocorticoid replacement. 

Thyroid stimulating hormone

Unrecognised hypothyroidism is associated with weight gain and menstrual disturbance, as well as growth failure in children.

Baseline TSH should be documented in all patients presenting with these symptoms. 


Women presenting later in life with oligomenorrhoea should be assessed for the common causes including hyperprolactinaemia.

Mild degrees of hyperprolactinaemia are also seen in PCOS and may not indicate pituitary or other pathology.

Testosterone, sex hormone binding globulin  

This should ideally be performed early morning, early follicular phase and off the contraceptive pill.

Testosterone is usually elevated in patients with classic and non classic CAH.

Sex hormone binding globulin is typically low in PCOS and Cushing’s.

Testosterone is typically but not always mildly elevated in PCOS. 

High levels in women with oligomenorrhoea or virilisation (>3.5nmol/l in the author's institution) should prompt a search for other causes, including CAH, virilising tumours or Cushing’s syndrome.

170H progesterone

This test is best performed early morning, early follicular phase and off the contraceptive pill.

17OHP is the most useful initial screen for congenital adrenal hyperplasia - if elevated above 10nmol/l, the patient will require full evaluation: a short synacthen test.

Levels above 50nmol/l are diagnostic of CAH.

Further investigations - selected cases only

Short synacthen test  

If the baseline 17 hydroxyprogesterone is elevated >10nmol/l, proceed to a synacthen test to confirm or exclude late onset congenital adrenal hyperplasia.


In neonates presenting with ambiguous genitalia, karyotype should be performed to help establish the underlying diagnosis, though this does not define gender assignation.


All patients in whom a biochemical diagnosis of CAH has been established should have genetic counselling and genotyping performed to confirm the diagnosis and allow prenatal counselling where possible.

Bone age

This is useful as accelerated bone age may indicate discordance with medications or under treatment.

Luteinising hormone, follicle stimulating hormone  

These are not necessary to diagnose CAH but may ge useful to help differentiate it from other causes of oligomenorrhoea in patients presenting in adulthood.

Elevated luteinising hormone: follicle stimulating hormone ratio is often seen in PCOS.

LH and FSH may both be low in pituitary and hypothalamic causes of oligomenorrhoea, for example associated with low body mass or anorexia or excessive exercise.

FSH will be elevated in the secondary amenorrhoea of premature ovarian failure.


This should be taken on day 21 of the menstrual cycle to indicate whether ovulation is occurring in adult patients seeking fertility.

Fasting glucose and lipids  

Essential for cardiovascular risk stratification in patients on glucocorticoid replacement therapy or with PCOS.

Androstenedione, dihydoepiandrosterone

These are not necessary in confirmed CAH, but are useful in other patients presenting with virilisation, with elevated testosterone, or with suspected Cushing’s syndrome. These are typically minimally elevated in PCOS, but much higher in Cushing’s and adrenal tumours.

2x24hr urinary free cortisols

Patients presenting in adulthood with virilisation but without known CAH should be assessed for possible Cushing's syndrome.

Urinary cortsiols form a sensitive but not specific initial screen for Cushing's and are usually performed with a low dose dexamethasone suppression test. 

Low dose dexamethasone suppression test

If there is a clinical suspicion of Cushing’s syndrome, a low dose dexamethasone suppression test should be performed to seek suppressibility of cortisol though this is not indicated in the investigation of CAH.

Transvaginal ovarian ultrasound scan

This may be useful to assess uterine development and size in women seeking fertility, but is not routinely required in patients with CAH.

Ovarian imaging (by ultrasound or MRI) is mandatory where there is a suspicion of virilising tumour.

MRI pelvis and adrenals

When a virilising tumour is strongly suspected but not visualised on ultrasound scan, MRI pelvis may be helpful and can be combined with adrenal imaging to avoid the abdominal radiation exposure necessary for an adrenal protocol CT scan in a young woman.

Testicular ultrasound scan

Male patients presenting with testicular masses need assessment to rule out sinister causes, though these are most likely to represent testicular adrenal rest "tumours": TARTs.