Lab Evaluation

  • Glucose, glucose, glucose (pre- and post-prandial)
  • Electrolytes, calculate anion gap
  • CBC (neutropenia, thrombocytopenia and anemia are often seen in organic acid disorders and in some OXPHOS disorders)
  • BUN (low BUN indicates failure of urea acid cycle, either primary or secondary)
  • Lactate, pyruvate, and L/P ratio
  • Raised Lactate with L/P 10-20 indicates a disorder of pyruvate metabolism such as PDH deficiency
  • Raised Lactate with L/P of > 20 indicates a disorder of oxidative phosphorylation
  • Ammonia (elevated; seen in urea acid cycle disorders, organic acid disorders)
  • Creatine Kinase (CK); often mildly elevated with muscle involvement
  • Biotinidase level (ataxia, seizures, rash after 6 months of life)
  • VLCFA (neonatal peroxisomal disorders)
  • Amino Acids (blood and urine)
  • Organic Acids (quantitative; post-parandial and fasting if deemed safe)
  • Acyl-carnitines (blood and urine)
  • Skin biopsy for EM and fibroblast culture
  • Muscle biopsy

Initial Laboratory Evaluation

Test

Tissue* 

Comment

Glucose

B

 

Electrolytes

B

 

Blood Counts

B

 

Lactate

B

Proper technique must be used; tourniquet must be released before blood is sampled

Ammonia

B

 

Metabolic Screen

B,U

The metabolic screen varies between hospitals, but may include screening testing for a variety of disorders as well as urine and blood amino acid profile, and screening organic acid testing

Ketones

B,U

Most valuable if collected at the time of an illness

 *B = blood, U = Urine

Secondary Laboratory Evaluation

Test

Tissue* 

Comment

Lactate

B,CSF

see above

Pyruvate

B

Proper determination of pyruvate requires the specimen be instantly deprotinized.  

L/P Ratio

B

The ratio of lactate to pyruvate can be very helpful in determing which type of disorder may be present

Amino Acids

B,U, CSF

Urine collections may be random or timed; and may be collected after a meal or after a fasting period, depending on the clinical situation. “Generalized aminoaciduria” may indicate the presence of a mitochondrial cytopathy, as well as other medical conditions.

Organic Acids

U, CSF

Samples must be kept refrigerated or frozen. Different techniques, some more sensitive are used by certain laboratories. Urine collections may be random or timed, and may be collected after a fasting period, depending on the clinical situation.

Carnitine Analysis

B,U

Most laboratories determine the free carnitine and total carnitine. Fractionation into specific acyl carnitines may be helpful in some situations. Urine collections may be random or timed, and may be collected after a fasting period, depending on the clinical situation.

Ketones

B,U

Fractionation of ketones into β-hydroxybuterate and acetoacetate may be helpful. This test is most valuable if collected during an acute illness or after a fast.

Free Fatty Acids

B

 

Mitochondrial DNA Point Mutations

B

If a patient fits into a specific, well-described mitochondrial phenotype, testing for specific, known point mutations may be helpful at this stage.

Mitochondrial DNA Southern Blot

B

If a patient fits into a specific, well-described mitochondrial phenotype, Southern blot testing may be helpful at this stage.

 *B = blood, U = Urine, CSF = Cerebral Spinal Fluid

Tertiary Laboratory Testing  

Test

Comment

Repeat Testing

Repeating some of the above listed tests, sometimes under different conditions (such as during an illness), may be helpful.

Provocative Testing

Under monitored conditions, usually in the hospital, repeating some of the above tests after a fast or after a specific meal or intravenous infusion, may be helpful. 

Skin Biopsy

A skin (also known as a fibroblast) culture can be established with the skin obtained from a biopsy. This can be sent for testing electron transport chain activity, β-oxidation disorders, as well as for a variety of other specific diseases.

Mitochondrial DNA Point Mutations

If a patient fits into a specific, well-described mitochondrial phenotype, testing for specific, known point mutations may be helpful at this stage.

Mitochondrial DNA Southern Blot

If a patient fits into a specific, well-described mitochondrial phenotype, Southern blot testing may be helpful at this stage.

Coenzyme Q10

Blood Test

Muscle Biopsy

Muscle tissue can be used for tests that can be diagnostic, even when the above tests are normal. Because this is the most invasive test, the risks and costs of the procedure must be weighed against the chance the biopsy will yield positive results and the benefits gained by a diagnosis (treatment decisions, family planning). Before a muscle biopsy is done a plan needs to be arranged for how the muscle is distributed. References labs should be contacted before the biopsy is done so that preparation of the muscle is done correctly. Muscle can be sent for:  

  • Routine light microscopy including modified Gomori Trichrome stain (checking for ragged red fibers)
  • Specific immunohistochemistry (cytochrome oxidase and COX subunits), succinate dehydrogenase, etc.
  • Electron microscopy (useful to view the structure of the mitochondria, evaluate for accumulation of excessive mitochondria in the subsarcolemma region and evaluate for mitochondrial proliferation).
  • Electric Transport Chain Activity (photometric analysis), preferably performed on fresh muscle but can be done on frozen muscle.
  • Oxidative Phosphorylation Activity (oxygen uptake), which can determine the activity of all five complexes, state iii and state iv respiration, respiratory control ratio and estimate efficiency of coupling of electron transport and oxidative phosphorylation. This can be run on fresh muscle only.
  • Enzyme activity for β-oxidation disorders including the enzymes of the β-oxidation spiral and carnitine transport.
  • Determination of carnitine and acyl-carnitine levels, Co-Enzyme Q10 levels.

Other Metabolic Tests That May Be Indicated in Certain Situations

Test

Tissue

Disease(s)

Comment

Uric Acid, Creatinine

B,U

Lesch-Nyhan

These patients often have lactic acidosis

Copper, Ceruloplasm

B,U

Menkes Kinky Hair Disease, Wilsons Disease, other movement disorders and dementias

 

Very Long Chain Fatty Acids

B

Adrenoleukodystrophy and other disorders of peroxisomal metabolism

 

Lysozomal Enzymes

B.U

variety of storage diseases and leukodystrophies 

 

Testing That May Be Necessary in Patients with Mitochondrial Cytopathies
Brain MRI, MRS
Eye: Retinal exam, electroretinogram
H
eart: EKG and echocardiogram
Thyroid Function Tests (blood)
Ears: Audiogram or BAEP

Additional testing information can be found in the "Diagnosis Toolkit" section of the Mitochondrial Medicine Society (MMS) website.

Except where noted, the above excerpts were taken, with permission, from Mitochondrial Cytopathies: A Primer written by Dr. Bruce Cohen, MD