Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCAD)MANAGEMENT

ENDOCRINE AND METABOLIC PRESENTATIONS · 12 SECTIONS

⚲

601 items

☷ Legend

⚲

Cardiovascular Presentations71▾

Respiratory Presentations52▾

Neurological Presentations83▾

Gastrointestinal Presentations74▾

Genitourinary and Reproductive Presentations48▾

Infectious Disease Presentations148▾

Trauma Presentations89▾

Toxicologic Presentations80▾

Psychiatric Presentations26▾

Musculoskeletal and Rheumatologic Presentations96▾

Dermatology Presentations23▾

Environmental and Exposure Presentations27▾

Hematologic and Oncologic Presentations36▾

Pediatric-Specific Presentations19▾

Endocrine and Metabolic Presentations45▾

Acute Porphyria Adrenal crisis Adrenal Insufficiency (Addisonian Crisis)Dehydration Diabetes Insipidus Diabetic Ketoacidosis (DKA)Euglycemic DKA (SGLT2 inhibitor)Galactosemia GLP-1 receptor agonist complications (retained gastric contents, aspiration risk)Homocystinuria Hypercalcemia Hyperkalemia Hypermagnesemia Hypernatremia Hyperosmolar Hyperglycemic State (HHS)Hypertensive emergency Hypertensive urgency Hypocalcemia Hypoglycemia Hypogonadism (Acute Presentation)Hypokalemia Hypomagnesemia Hyponatremia Hypoparathyroidism (Tetany)Insulin pump failure Maple Syrup Urine Disease (Crisis)Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCAD)Metabolic Acidosis Metabolic Alkalosis Myasthenia gravis crisis Myxedema coma Pellagra Pheochromocytoma (Crisis)Pituitary Apoplexy Pompe Disease (GSD II)Respiratory Acidosis Respiratory Alkalosis Scurvy SIADH Starvation Ketosis Tarui Disease (GSD VII)Thyroid storm Tyrosinemia Vitamin D Deficiency (Severe-Rickets)Von Gierke Disease (GSD I)

ENT and Maxillofacial Presentations27▾

Ophthalmologic Presentations19▾

Obstetric Presentations23▾

Systemic and Miscellaneous Presentations17▾

01Approach to the Critical Patient/attcp46

Immediate stabilization

›Hypoglycemia crisis recognition

›Point-of-care glucose immediately on arrival

›Threshold for critical action: glucose < 2.8 mmol/l (< 50 mg/dL)

›Target during resuscitation: glucose 5.5–6.7 mmol/l (100–120 mg/dL)

›Hypoketotic hypoglycemia pattern

›Absent or low urine ketones despite significant hypoglycemia

›Elevated free fatty acids with paradoxically low ketones

›If altered mental status or glucose < 2.8 mmol/l, initiate IV dextrose immediately

›D10W bolus 2–5 mL/kg IV over 5–10 minutes

›Follow with continuous D10W infusion at 1.5× maintenance

›Airway and neurologic threats

›Seizure activity from severe hypoglycemia

›IV benzodiazepine if active seizure

›Treat underlying hypoglycemia as primary intervention

›Altered mental status — GCS < 13

›Position lateral decubitus to protect airway

›Immediate IV access and glucose correction

›Apnea or respiratory arrest

›Bag-mask ventilation, escalate to intubation if no rapid response

›Reported especially in neonatal MCAD presentations

Monitoring and targets

›Glucose monitoring protocol

›Point-of-care glucose every 30 minutes until stabilized

›Target glucose > 5.5 mmol/l on continuous infusion

›Do not reduce IV dextrose rate until oral intake is reliably > 75% of normal

›Glucose infusion rate target 8–12 mg/kg/min in infants

›Higher rates may be required in severe decompensation

02History/hx64

Presenting symptoms

›Core metabolic crisis symptoms

›Lethargy and decreased responsiveness

›Can progress from irritability to coma within hours

›Vomiting

›Often triggered by intercurrent illness

›Exacerbates fasting state

›Poor feeding or refusal to feed

›Compounds fasting duration and metabolic stress

›Neurological symptoms

›Altered mental status

›Irritability

›Excessive sleepiness

›Difficulty waking

›Seizure activity

›Hypoglycemic seizures — most common mechanism

Triggers and timeline

›Precipitating event characterization

›Duration of fasting before symptom onset

›Critical parameter — longer fast predicts worse presentation

›Typical: symptoms after 6–12 hours fasting

›Intercurrent illness type

›Gastroenteritis — most common trigger

›Upper respiratory infection with fever

›Any febrile illness with reduced oral intake

›Recent weaning from nighttime feedings

›Classic trigger between 4–12 months of age

›Age of presentation

03Physical Exam/exam39

Vital signs and general appearance

›Vital sign interpretation

›Tachycardia

›Marker of metabolic stress, hypoglycemia, and underlying illness

›Hypothermia

›Late and ominous sign — severe metabolic decompensation

›Fever

›Identifies intercurrent infectious trigger

›Hypotension

›Indicates severe decompensation or sepsis coexisting

›General appearance

›Pallor and diaphoresis

›Adrenergic response to hypoglycemia

›Decreased tone

›Hypotonia during active crisis

›Between episodes: completely normal appearance

›Key clinical feature — normal exam does not exclude diagnosis

Neurological examination

›Level of consciousness

›GCS or AVPU scale

›Baseline GCS expected when well

›Altered GCS triggers immediate glucose correction

›Irritability or paradoxical response to stimulation

›Early encephalopathy marker

›Seizure assessment

›Focal versus generalized

›Focal raises concern for structural injury from prior hypoglycemia

›Postictal state recognition

04Differential Diagnosis/ddx34

Fatty acid oxidation disorders

›VLCAD deficiency (very long-chain acyl-CoA dehydrogenase deficiency)

›ICD-10: E71.310

›Distinguished by C14:1 elevation on acylcarnitine profile

›Also causes cardiomyopathy and rhabdomyolysis — not seen in MCAD

›LCHAD deficiency

›ICD-10: E71.312

›Long-chain 3-OH acylcarnitines (C16-OH, C18-OH) elevated

›Additional features: peripheral neuropathy, retinopathy, maternal AFLP

›Multiple acyl-CoA dehydrogenase deficiency (MADD / Glutaric aciduria type II)

›ICD-10: E71.313

›Broad elevations across multiple chain lengths on acylcarnitine profile

›More severe, often neonatal presentation with dysmorphic features

Hypoglycemia mimics

›Hyperinsulinism

›ICD-10: E16.1

›Hypoglycemia with suppressed ketones AND suppressed free fatty acids

›In MCAD, free fatty acids are elevated — key differentiator

›Glycogen storage diseases

›ICD-10: E74.0x

›Hepatomegaly and hypoglycemia but ketotic response preserved

›Fasting tolerance and enzyme panels differentiate

›Reye syndrome

›ICD-10: G93.7

›Historically confused with MCAD before acylcarnitine testing

›Aspirin exposure, mitochondrial changes on liver biopsy

›No characteristic C8 acylcarnitine elevation

05Laboratory Tests/lt49

Point-of-care and urgent labs

›Point-of-care glucose

›Obtain immediately on arrival

›Critical threshold: < 2.8 mmol/l (< 50 mg/dL) in children

›Repeat every 30 minutes until stable

›Obtain prior to starting IV glucose if possible

›Biochemical markers normalize rapidly with glucose treatment

›Venous blood gas

›Metabolic acidosis during crisis

›Elevated anion gap from organic acid accumulation

›pH, bicarbonate, and lactate interpretation

›Lactate may be mildly elevated secondary to metabolic stress

Diagnostic metabolic labs

›Plasma acylcarnitine profile (tandem MS/MS)

›Elevated C8 (octanoylcarnitine) — primary diagnostic marker

›C8 > 0.3 µmol/L on dried blood spot is diagnostic threshold

›Elevated C6 (hexanoylcarnitine) and C10 (decanoylcarnitine)

›C8/C10 ratio > 5

›Highly specific for MCAD deficiency

›C8/C2 ratio elevation

›Additional diagnostic support

›Collect before glucose correction if clinically safe

›Urine organic acids

›Medium-chain dicarboxylic acids

›Hexanoylglycine, octanoylglycine, decanoylglycine

›Suberylglycine — characteristic of MCAD

›Phenylpropionylglycine may be present

›Elevates with certain MCT-containing ingestions

06Diagnostic Tests/dt49

Scoring Systems

›No validated ED severity score specific to MCAD crisis

›Risk stratification based on clinical and biochemical parameters

›Severe: GCS < 13, glucose < 1.7 mmol/l, active seizures

›Moderate: lethargy, glucose 1.7–2.8 mmol/l, tolerating some fluids

›Mild: irritability only, glucose > 2.8 mmol/l, tolerating oral intake

›Genotype-phenotype correlation

›Homozygous c.985A>G (p.Lys329Glu) — more severe phenotype

›Higher C8 levels on NBS and clinical acylcarnitine profiles

›Higher frequency of hypoglycemic episodes

›Higher transaminase elevations at baseline

›Compound heterozygotes — variable severity

›Depends on residual MCAD enzyme activity of each allele

MRI

›Brain MRI indications in MCAD

›Neurologic sequelae evaluation after hypoglycemic crisis

›Not required for acute metabolic crisis management

›Indicated for persistent neurological deficit after normoglycemia

›Findings from hypoglycemic brain injury

›Basal ganglia injury — bilateral signal abnormality on DWI/T2

›Cortical injury — watershed or diffuse cortical signal change

›Posterior fossa involvement possible with severe neonatal hypoglycemia

›MRI protocol

›DWI sequences most sensitive in acute phase (< 7 days)

›T2/FLAIR sequences for chronic injury assessment

›Spectroscopy — may show lactate peak in affected areas

›Not typically needed for clinical management

07Disposition/dispo36

Admission criteria

›Indications for inpatient admission

›Hypoglycemia on presentation regardless of subsequent response

›Minimum overnight observation recommended even if recovered

›AAP guideline: do not discharge after single glucose correction without observation

›Altered mental status or seizures

›Requires neurology consultation and monitoring

›Inability to tolerate oral intake

›Active vomiting or diarrhea preventing oral hydration

›Ongoing infectious illness

›Fasting risk persists until illness resolves

›ICU-level criteria

›Persistent altered mental status after glucose normalization

›GCS < 13 at 30 minutes post-correction

›Active or refractory seizures

›Cardiac arrhythmia

›Neonatal presentation with suspected MCAD

Discharge criteria

›Safe discharge checklist

›Tolerating > 75% of typical oral intake without emesis

›At least 2 hours of observed oral tolerance in ED

›Normoglycemia maintained off IV dextrose

›Glucose > 4.4 mmol/l on room air without glucose infusion

›Underlying illness improving

›Fever trending down, hydration adequate

›Return precautions understood by caregiver

›Written instructions provided

›Transfer criteria

08Treatment/t80

Immediate glucose resuscitation

›IV dextrose bolus for symptomatic hypoglycemia

›D10W 2–5 mL/kg IV bolus over 5–10 minutes

›Repeat if glucose does not reach > 4.4 mmol/l within 15 minutes

›Do not use D25W or D50W in children — osmotic risk

›Check glucose 15 minutes after bolus

›If inadequate response, repeat bolus and increase infusion rate

›Continuous glucose infusion

›D10W at 1.5× maintenance rate

›Glucose infusion rate target: 8–12 mg/kg/min in infants

›6–8 mg/kg/min in older children

›Titrate infusion to maintain glucose 5.5–6.7 mmol/l

›Check glucose every 30 minutes until stable

›Do not reduce infusion rate until oral intake confirmed > 75% of normal

›Add electrolytes to maintenance fluid

›Correct hyponatremia, hypokalemia

›Avoid hypotonic fluids in encephalopathic child

Carnitine supplementation

›L-carnitine administration

›Oral L-carnitine: 25–100 mg/kg/day divided every 8–12 hours

›Use when free carnitine < 20 µmol/l confirms secondary deficiency

›Practice varies by center — defer to metabolic specialist guidance

›IV L-carnitine: 50 mg/kg/day divided every 6 hours

›Reserved for severe decompensation or inability to tolerate oral route

›100 mg/kg IV loading dose used at some centers

›Controversy: routine supplementation in MCAD not universally recommended

›Some centers supplement only when carnitine levels are low

›Follow patient's emergency letter guidance if available

Contraindicated medications

›Absolute contraindications in MCAD

›Valproic acid

›Inhibits fatty acid oxidation at multiple steps

›Dramatically worsens metabolic decompensation

›NSAIDs and salicylates

›Inhibit FAO; salicylates risk Reye-like syndrome

›Acetaminophen is safe alternative for analgesia and antipyresis

›IV lipid emulsions (e.g., TPN lipids)

›Avoid during acute decompensation

›Medium-chain lipids cannot be metabolized — accumulate toxic intermediates

›Triheptanoin

›Requires functional MCAD for metabolism

›Contraindicated in MCAD deficiency specifically

Treat underlying trigger

›Infectious illness management

›Antipyretics — acetaminophen preferred

›15 mg/kg/dose orally or rectally every 4–6 hours

›Ibuprofen is contraindicated

›Antibiotics if bacterial infection confirmed

›Do not withhold antibiotics to wait for metabolic results

›Antiemetics for persistent vomiting

›Ondansetron 0.15 mg/kg IV/IM/oral (max 4 mg < 6 yr, 8 mg > 6 yr)

›Facilitates oral carbohydrate intake and hydration

Seizure management

›Hypoglycemic seizures

›Treat hypoglycemia as primary intervention

›D10W bolus 2–5 mL/kg IV if no IV access yet

›Intranasal or buccal glucose gel if IV access delayed

›Benzodiazepine for active seizure

›Midazolam 0.1–0.2 mg/kg IV/IM/intranasal

›Lorazepam 0.05–0.1 mg/kg IV

›Anti-epileptic loading only if seizures persist after normoglycemia

›Levetiracetam 20 mg/kg IV preferred (no FAO inhibition)

›Avoid valproic acid — absolutely contraindicated

Chronic outpatient management

›Fasting avoidance protocol

›Birth to 4 months: maximum fast 4 hours

›Night feedings must not be skipped

›5–12 months: maximum fast increases by 1 hour per month of age

›At 6 months: 6-hour maximum; at 10 months: 10-hour maximum

›Age > 1 year: maximum fast 12 hours for life

›Bedtime snack or 2 g/kg uncooked cornstarch before longest fast

›Dietary management

›No more than 30% of total daily energy from fat

›Normal carbohydrate-based diet otherwise

›Avoid MCT oil, coconut oil, MCT-supplemented formulas

›Medium-chain fats cannot be metabolized

›Illness protocol: push simple carbohydrates early

›Juice, glucose tablets, sweetened non-diet beverages

›Do not wait for symptoms to begin carbohydrate loading

›Emergency preparedness

›MedicAlert bracelet at all times

›Identifies MCAD diagnosis and emergency contacts

›Emergency letter from metabolic specialist

›Share with schools, daycares, babysitters, all medical providers

›Pre-surgical planning mandatory

›Contact metabolic center before any fasting procedure

09Special Populations/sp60

Pregnancy

›Maternal MCAD deficiency considerations

›Maternal MCAD is generally well tolerated during pregnancy

›Fasting avoidance remains critical, especially during hyperemesis

›Increased caloric needs in third trimester require dietary adjustment

›Risk of acute fatty liver of pregnancy (AFLP)

›More strongly associated with maternal LCHAD deficiency than MCAD

›Monitor liver function in third trimester if MCAD diagnosed

›Neonatal considerations of maternal MCAD status

›If mother has MCAD, infant has 50% carrier risk

›Infant will be identified on NBS if affected

›False-negative NBS possible if maternal carnitine levels confound sample

›Breastfeeding is safe and encouraged

›Breastfed infants may have mildly higher C8 on NBS

›Ensure early establishment of adequate milk supply

›Medication safety in pregnancy with MCAD

›L-carnitine supplementation: considered safe in pregnancy

›Category B — use if maternal carnitine deficiency documented

›Valproic acid: absolutely contraindicated (teratogen + FAO inhibition)

›Acetaminophen: safe for antipyresis and analgesia

Geriatric

›Adult and late-onset MCAD presentations

›Rare but reported — typically undiagnosed mild phenotype

›Prolonged exercise-induced rhabdomyolysis

›Fasting-induced muscle weakness and myalgia

›Diagnostic acylcarnitine profile remains the same

›C8 elevation may be less pronounced in mild variants

›Long-term complications in older diagnosed patients

10Background/b73

Epidemiology

›Incidence and prevalence

›Most common inherited fatty acid oxidation disorder

›US incidence: 1:13,000–1:19,000 live births

›European incidence varies: 1:8,000–1:17,000 depending on population

›Northern European ancestry — highest incidence

›Founder effect for c.985A>G variant in this population

›Autosomal recessive inheritance

›ACADM gene on chromosome 1p31

›Carrier frequency approximately 1:40–1:100 in Northern Europeans

›Genetic epidemiology

›c.985A>G (p.Lys329Glu) variant — most common mutation

›Accounts for approximately 81% of disease alleles in clinically identified patients

›Homozygous c.985A>G in ~73% of affected Northern Europeans

›Over 40 other disease-causing ACADM variants identified

›Many private mutations in non-Northern European populations

›Impact of newborn screening

›Newborn screening dramatically changed disease course

›Before NBS: up to 18% of first presentations were fatal

›After universal NBS: most patients identified presymptomatically

›Pre-NBS era: estimated mortality 18–25% with first metabolic crisis

›Majority of SIDS/sudden unexplained infant deaths now recognized

›Sudden neonatal death remains possible before NBS result available

›Especially in first 1–2 days of life

Pathophysiology

›Enzyme defect and metabolic consequences

›MCAD enzyme — mitochondrial enzyme in fatty acid beta-oxidation

›Catalyzes dehydrogenation of medium-chain acyl-CoA esters (C6–C12)

›ACADM gene mutation produces non-functional or absent MCAD protein

›Impaired beta-oxidation of medium-chain fatty acids

›C8 (octanoyl-CoA), C10 (decanoyl-CoA), C12 (lauroyl-CoA) cannot be oxidized

›Accumulation of toxic acylcarnitine intermediates

›Energy failure mechanism

›Ketone body synthesis requires fatty acid oxidation

›During fasting, gluconeogenesis depends on hepatic ketogenesis

›MCAD deficiency blocks ketone production from medium-chain fats

›Hypoketotic hypoglycemia is the result

›Brain and heart depend on ketones during fasting — deficit causes crisis

›Free fatty acids are elevated (mobilized but not oxidized)

›Toxicity of accumulated intermediates

›Octanoic acid and related metabolites are directly toxic

›Mitochondrial dysfunction at high concentrations

›Hyperammonemia via inhibition of urea cycle enzymes

›Secondary carnitine deficiency

›Acylcarnitine formation sequesters free carnitine

›Free carnitine depletion further impairs mitochondrial function

›Trigger physiology

›Normal state: adequate glycogen stores maintain glucose without fat oxidation

›MCAD patients are clinically well when fed and not ill

›Fasting or illness depletes glycogen

›Fatty acid oxidation required but fails at medium-chain step

›Rapid development of hypoglycemia and encephalopathy

Therapeutic Considerations

›Evidence base for acute management

›AAP 2021 guidelines — primary reference for acute illness management

›D10W continuous infusion at 1.5× maintenance is standard of care

›Do not reduce IV glucose until oral intake confirmed adequate

›Immediate triage prioritization

›AAP recommends MCAD patients not wait in triage — immediate evaluation

›L-carnitine evidence

›Rationale: replenish secondary carnitine deficiency from acylcarnitine accumulation

›Theoretical: may improve clearance of toxic acylcarnitines

›Evidence: observational only — no RCTs demonstrating outcome benefit

›Practice varies by center; some supplement only when free carnitine < 20 µmol/l

›Safety: generally well tolerated; avoid IV lipid vehicles

›Fasting tolerance guideline evidence

›Age-based fasting limits from pediatric metabolic consensus

›Derived from fasting studies and clinical experience — not RCT data

›Supported by long-term outcome data showing no complications when adhered to

›Expected prognosis with adherence: no irreversible complications in one longitudinal cohort

›Investigational therapies

›Heptanoic acid and medium branched-chain fatty acids

›Anaplerotic substrates that bypass MCAD enzyme step

›Under investigation — not standard of care

›Gene therapy

›Preclinical research stage — not clinically available

11Patient Discharge Instructions/pdi47

copy discharge instructions

›Diagnosis explanation

›Your child has MCAD deficiency, a metabolic condition affecting how the body uses certain fats for energy

›The body cannot burn medium-chain fats during fasting or illness

›This causes dangerously low blood sugar (hypoglycemia) without ketones

›MCAD is a lifelong condition that is very manageable with proper precautions

›Most people live completely normal lives with careful fasting management

›Critical fasting rules

›Never fast longer than the following limits

›0–4 months: no more than 4 hours without feeding

›5–12 months: no more than 1 hour per month of age (e.g., 8 hours at 8 months)

›Over 1 year of age: no more than 12 hours of fasting for life

›Always give a bedtime snack or cornstarch before the overnight fast

›Uncooked cornstarch 2 g/kg is effective as a slow-release carbohydrate

›Illness emergency protocol

›During any illness with vomiting, fever, or reduced appetite

›Push simple carbohydrates immediately — juice, glucose tablets, sweetened beverages

›Do not wait for symptoms before starting extra carbohydrates

›Contact your metabolic specialist or come to the ED early

›Foods and drinks to push during illness

›Apple juice, grape juice, Pedialyte with sugar, regular (not diet) popsicles

›Glucose tablets if available at home

›Foods and substances to avoid

›MCT oil, coconut oil, MCT-supplemented nutrition products

›Medium-chain fats cannot be metabolized and accumulate as toxins

›NSAIDs: ibuprofen (Advil, Motrin), naproxen

›Use acetaminophen (Tylenol) instead for pain and fever

›Aspirin and aspirin-containing products

12References/r24

Guidelines and key sources

›McGregor TL, Berry SA, Dipple KM, Hamid R. Management Principles for Acute Illness in Patients With Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency. Pediatrics. 2021

›Primary AAP guideline for acute ED and inpatient management

›D10W 1.5× maintenance, fasting limits, triage priority recommendations

›Chang IJ, Lam C, Vockley J. Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency. GeneReviews. 2024

›Comprehensive genetics and phenotype review

›Genotype-phenotype correlations, c.985A>G variant data, long-term outcomes

›Anderson DR, Viau K, Botto LD, Pasquali M, Longo N. Clinical and Biochemical Outcomes of Patients With Medium-Chain Acyl-CoA Dehydrogenase Deficiency. Molecular Genetics and Metabolism. 2020

›Longitudinal outcomes data

›No irreversible complications observed with adherence to fasting protocols

Supporting literature

›Van Hove JL, Zhang W, Kahler SG, et al. Medium-Chain Acyl-CoA Dehydrogenase (MCAD) Deficiency: Diagnosis by Acylcarnitine Analysis in Blood. American Journal of Human Genetics. 1993

›Foundational acylcarnitine diagnostic criteria

›C8 threshold and ratio data

›Hsu HW, Zytkovicz TH, Comeau AM, et al. Spectrum of MCAD Deficiency Detected by Newborn Screening. Pediatrics. 2008

›NBS population data and clinical spectrum

›Impact of universal screening on mortality

›Mütze U, Nennstiel U, Odenwald B, et al. Sudden Neonatal Death in Individuals With MCAD Deficiency: Limit of Newborn Screening. European Journal of Pediatrics. 2022

›Neonatal mortality risk before NBS result available

›Supports immediate triage for suspected neonatal MCAD

›Wang SS, Fernhoff PM, Hannon WH, Khoury MJ. Medium Chain Acyl-CoA Dehydrogenase Deficiency Human Genome Epidemiology Review. Genetics in Medicine. 2001

›Epidemiology and population genetics

›Incidence data, carrier frequency, Northern European founder effect

›Weiss KJ, Berger U, Haider M, et al. Free carnitine concentrations and biochemical parameters in MCAD deficiency: Genotype-phenotype correlation. Clinical Genetics. 2023

›Carnitine levels and supplementation evidence

›Guides threshold-based supplementation approach

Learn More: Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCAD)→

Comprehensive Clinical Review

Structured, evidence-informed, long-form analysis for deeper understanding.

Evidence & Review

Reviewed by SymptomDx Medical Team · Last reviewed August 18, 2026

SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.