Congenital Adrenal Hyperplasia

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Congenital Adrenal Hyperplasia (CAH) - Comprehensive Test Guide

Why is it done?
- Detects inherited enzyme deficiencies (primarily 21-hydroxylase deficiency) affecting cortisol and aldosterone production in the adrenal glands
- Newborn screening performed within 24-48 hours after birth to identify affected infants before symptoms develop
- Diagnostic confirmation in children or adults with clinical signs of CAH (ambiguous genitalia, salt-wasting, precocious puberty, or virilization)
- Genetic counseling and family screening to identify carriers and affected relatives
- Prenatal diagnosis in high-risk families with previous affected children
- Initial evaluation typically performed in first week of life; diagnostic testing may be repeated at 1-2 weeks for confirmation
Normal Range
- 17-Hydroxyprogesterone (17-OHP) - Primary Screening Marker: Newborns: <2.0 ng/mL (some labs: <40 nmol/L) - normal/negative Elevated cutoff typically >10 ng/mL on dried blood spot (varies by laboratory) Units: ng/mL or nmol/L depending on methodology
- Cortisol Levels: Morning (8 AM): 10-20 mcg/dL (275-555 nmol/L) - normal Elevated or low levels may indicate abnormality
- ACTH (Adrenocorticotropic Hormone): Normal range: 10-46 pg/mL (2-10 pmol/L) - baseline Elevated levels suggest adrenal insufficiency
- Androgen Markers (DHEA-S, testosterone): DHEA-S in newborns: typically <50-150 mcg/dL - normal range age-dependent Elevated levels in CAH due to enzyme block
- Aldosterone and Plasma Renin Activity (PRA): Aldosterone: 4-30 ng/dL (supine, normal sodium diet) - varies with form of CAH PRA: 0.5-1.6 ng/mL/hr - elevated in salt-wasting form
- Interpretation Key: NEGATIVE: All markers within normal range; CAH excluded BORDERLINE: Levels slightly elevated; may require repeat testing at 1-2 weeks POSITIVE: Elevated 17-OHP with clinical correlation; confirmatory testing needed
Interpretation
- Elevated 17-Hydroxyprogesterone (17-OHP): Suggests 21-hydroxylase deficiency (most common form, ~90% of CAH cases) Proximal blockade causes accumulation of precursor hormones Requires confirmatory testing with repeat measurement or ACTH stimulation test
- Elevated ACTH with Low/Normal Cortisol: Indicates primary adrenal insufficiency ACTH feedback loop elevated due to inadequate cortisol production Typical finding in both classic salt-wasting and simple virilizing forms
- Markedly Elevated Androgens (DHEA-S, Testosterone): Indicates enzyme block shunting substrates toward androgen synthesis More pronounced elevation in simple virilizing and salt-wasting forms May present as virilization in females or precocious puberty in males
- Low Aldosterone with Elevated PRA: Characteristic of salt-wasting CAH form (most severe presentation) Indicates deficient mineralocorticoid production Clinical signs: hyponatremia, hyperkalemia, hypotension, poor feeding
- ACTH Stimulation Test Results: Post-ACTH 17-OHP >1000 ng/dL strongly supports CAH diagnosis Post-ACTH cortisol response (normally >18 mcg/dL) blunted in CAH Used for definitive confirmation and carrier detection
- Factors Affecting Results: Timing of sample collection (false positives from sample taken <24 hours) Illness, stress, or fever may elevate 17-OHP and other hormones Prematurity or low birth weight associated with delayed enzyme maturation Medication use (dexamethasone therapy affects hormone levels) Laboratory variation in cutoff values and assay methodology
- Clinical Classification: CLASSIC SALT-WASTING (most severe): Severe 17-OHP elevation, ACTH↑, cortisol↓, aldosterone↓, PRA↑ CLASSIC SIMPLE VIRILIZING: Severe 17-OHP elevation, ACTH↑, cortisol↓-normal, androgens↑↑ NON-CLASSIC (late-onset): Mild 17-OHP elevation, milder clinical features, normal or near-normal newborn screen
Associated Organs
- Primary Organ System - Adrenal Cortex: Site of enzyme defects causing hormone synthesis impairment Bilateral adrenal hyperplasia develops as gland attempts to maintain hormone production
- Hypothalamic-Pituitary-Adrenal (HPA) Axis: Dysregulation with increased ACTH secretion compensating for low cortisol Pituitary gland shows adaptive response to adrenal insufficiency
- Reproductive/Genital System: Ambiguous genitalia in phenotypic females due to excess androgens in utero Virilization of external genitalia (Tanner staging changes) Risk of undescended testes or cryptorchidism in males
- Cardiovascular/Renal System: Salt-wasting form causes renal sodium loss and circulatory collapse risk Hyponatremia, hypokalemia, hypovolemia in severely affected infants Potential shock and cardiac arrhythmias if untreated
- Skeletal System: Accelerated bone maturation and advanced growth velocity in childhood Risk of early epiphyseal closure limiting final adult height Potential for reduced bone mineral density with chronic steroid therapy
- Associated Conditions/Complications: Acute adrenal crisis (hypovolemia, hypoglycemia, shock) - medical emergency Gender identity/psychological concerns from ambiguous genitalia in females Growth and developmental delays if inadequately treated Increased risk of metabolic syndrome and cardiovascular disease in adulthood Hypertension potential in some treated patients due to steroid therapy Infertility concerns due to excess androgens affecting reproductive development
Follow-up Tests
- Initial Confirmatory Testing (if newborn screening positive): Repeat 17-OHP measurement at 1-2 weeks of age for confirmation ACTH stimulation test (cosyntropin challenge) for definitive diagnosis Baseline electrolytes (sodium, potassium, chloride, bicarbonate) Baseline glucose and blood urea nitrogen (BUN) for metabolic assessment
- Differential Diagnosis Workup: 11-beta-hydroxylase enzyme activity assessment (alternative CAH form) 3-beta-hydroxysteroid dehydrogenase testing (rare CAH variant) 17-alpha-hydroxylase assay if atypical presentation Genetic testing (CYP21A2 mutation analysis) for molecular confirmation
- Extended Hormone Panel (post-diagnosis): Androstenedione levels (elevated in CAH) DHEA-S quantification LH (luteinizing hormone) and FSH (follicle-stimulating hormone) assessment Testosterone/DHT measurements Aldosterone and PRA for mineralocorticoid status evaluation
- Imaging Studies: Pelvic ultrasound to assess internal reproductive anatomy (in females) Abdominal ultrasound to evaluate adrenal gland enlargement Bone age assessment (skeletal survey) if advanced growth velocity MRI for complex anatomical evaluation if needed
- Genetic Testing and Counseling: CYP21A2 sequencing for genetic mutation identification CYP21A2 gene deletion/duplication analysis Carrier screening for family members (parents, siblings) Prenatal diagnosis in subsequent pregnancies (amniocentesis or CVS at 10-12 weeks)
- Monitoring Frequency (Ongoing Management): First 2 weeks: Daily clinical assessment with electrolytes if salt-wasting form First month: Weekly hormone panels and electrolytes Months 2-12: Biweekly to monthly assessment, then quarterly after age 1 Long-term: Every 3-6 months during childhood, then annually as adult During illness/stress: More frequent monitoring and possible dose adjustments
- Related Complementary Tests: Synacthen (cosyntropin) stimulation - assess adrenal reserve capacity Low-dose dexamethasone suppression test - assess feedback regulation 24-hour urinary free cortisol for overall hormone assessment Thyroid function panel (TSH, free T4) - rule out other endocrine conditions Growth hormone and IGF-1 if growth concerns Metabolic panel including glucose, calcium, phosphate
Fasting Required?
- Fasting Status: No fasting required for most CAH screening and diagnostic tests
- Newborn Screening (Dried Blood Spot): No fasting needed; performed on all newborns within 24-48 hours of birth Standard heel prick collection on filter paper card Fed or unfed status does not affect results
- Serum/Plasma Hormone Testing: No fasting strictly required; however, morning samples (8-10 AM) preferred for circadian hormone variation Fasting may be beneficial for concurrent metabolic panel assessment Timing consistency important for serial follow-up comparisons
- ACTH Stimulation Test: Recommended fasting 8-12 hours prior to test for baseline blood draw Early morning collection (7-8 AM) required for proper timing Fasting helps with concurrent metabolic/electrolyte assessment
- Medication/Preparation Restrictions: DO NOT discontinue cortisol/hydrocortisone replacement therapy Mineralocorticoid (fludrocortisone) may be continued unless otherwise directed If on dexamethasone, inform laboratory (cross-reacts with some assays) Recent steroid administration may falsely suppress 17-OHP levels Hold stimulating medications (ACTH, corticotropin) until test completion
- Patient Preparation Requirements: Rest for 30 minutes prior to sampling (stress can elevate ACTH/cortisol) Stress reduction important; schedule non-urgent testing when possible Illness, fever, or acute stress elevates hormone levels; defer non-emergent testing Note current medications and their timing with lab draw Document recent trauma, surgery, or extreme stress (affects hormone levels) For stimulation tests: ensure IV line established at least 30 minutes prior to baseline Recumbent position for 30 minutes before morning collection Avoid caffeine and nicotine 2 hours before testing
- Specimen Collection Notes: Serum samples: Allow blood to clot, then centrifuge; use SST tube typically Plasma samples: EDTA (lavender) or heparin (green) tube per lab specification Rapid transport to laboratory on ice for sensitive hormones ACTH samples: Special pre-chilled collection with EDTA, transport on ice immediately Dried blood spot cards: Allow to air dry completely before mailing (48 hours minimum)

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