In most regions, galactosemia is diagnosed as a result of newborn screening, most commonly by determining the concentration of galactose in a dried blood spot. Some regions will perform a second-tier test of GALT enzyme activity on samples with elevated galactose, while others perform both GALT and galactose measurements. While awaiting confirmatory testing for classic galactosemia, the infant is typically fed a soy-based formula, as human and cow milk contains galactose as a component of lactose. Confirmatory testing would include measurement of enzyme activity in red blood cells, determination of Gal-1-P levels in the blood, and mutation testing. The differential diagnosis for elevated galactose concentrations in blood on a newborn screening result can include other disorders of galactose metabolism, including galactokinase deficiency and galactose epimerase deficiency. Enzyme assays are commonly done using fluorometric detection or older radioactively labeled substrates.

One of, if not the most common form of organic acidemia, methylmalonic acidemia is not apparent at birth as symptoms usually do not present themselves until proteins are added to the infant's diet. Because of this, symptoms typically manifest anytime within the first year of life. Due to the severity and rapidity in which this disorder can cause complications when left undiagnosed, screening for methylmalonic acidemia is often included in the newborn screening exam.

Because of the inability to properly break down amino acids completely, the byproduct of protein digestion, the compound methylmalonic acid, is found in a disproportionate concentration in the blood and urine of those afflicted. These abnormal levels are used as the main diagnostic criteria for diagnosing the disorder. This disorder is typically determined through the use of a urine analysis or blood panel. The presence of methylmalonic acidemia can also be suspected through the use of a CT or MRI scan or ammonia test, however these tests are by no means specific and require clinical and metabolic/correlation. Elevated levels of ammonia, glycine, and ketone bodies may also be present in the blood and urine.

The term homocystinuria describes an increased excretion of the thiol amino acid homocysteine in urine (and incidentally, also an increased concentration in plasma). The source of this increase may be one of many metabolic factors, only one of which is CBS deficiency. Others include the re-methylation defects (cobalamin defects, methionine sythase deficiency, MTHFR) and vitamin deficiencies (cobalamin (vitamin B12) deficiency, folate (vitamin B9) deficiency, riboflavin deficiency (vitamin B2), pyridoxal phosphate deficiency (vitamin B6)). In light of this information, a combined approach to laboratory diagnosis is required to reach a differential diagnosis.

CBS deficiency may be diagnosed by routine metabolic biochemistry. In the first instance, plasma or urine amino acid analysis will frequently show an elevation of methionine and the presence of homocysteine. Many neonatal screening programs include methionine as a metabolite. The disorder may be distinguished from the re-methylation defects (e.g., MTHFR, methionine synthase deficiency and the cobalamin defects) in lieu of the elevated methionine concentration. Additionally, organic acid analysis or quantitative determination of methylmalonic acid should help to exclude cobalamin (vitamin B12) defects and vitamin B12 deficiency giving a differential diagnosis.

The laboratory analysis of homocysteine itself is complicated because most homocysteine (possibly above 85%) is bound to other thiol amino acids and proteins in the form of disulphides (e.g., cysteine in cystine-homocysteine, homocysteine in homocysteine-homocysteine) via disulfide bonds. Since as an equilibrium process the proportion of free homocystene is variable a true value of total homocysteine (free + bound) is useful for confirming diagnosis and particularly for monitoring of treatment efficacy. To this end it is prudent to perform total homocyst(e)ine analysis in which all disulphide bonds are subject to reduction prior to analysis, traditionally by HPLC after derivatisation with a fluorescent agent, thus giving a true reflection of the quantity of homocysteine in a plasma sample.

Methylmalonic acidemia has varying diagnoses, treatment requirements and prognoses, which are determined by the specific genetic mutation causing the inherited form of the disorder. The following are the known genotypes responsible for methylmalonic acidemia:

The mut type can further be divided in mut0 and mut- subtypes, with mut0 characterized by a complete lack of methylmalonyl CoA mutase and more severe symptoms and mut- characterized by a decreased amount of mutase activity.

Mut-, cblB, and cblA versions of methylmalonic acidemia have been found to be cobalamin responsive. Mut0 is a nonresponsive variant.

Autozygome analysis and biochemical evaluations of urinary sugars and polyols can be used to diagnose Transaldolase Deficiency. Two specific methods for measuring the urinary sugars and polyols are liquid chromatographytandem mass spectrometry and gas chromatography with flame ionization detection.

Direct sequence analysis of genomic DNA from blood can be used to perform a mutation analysis for the TALDO1 gene responsible for the Transaldolase enzyme.

Because LAL deficiency is inherited, each sibling of an affected individual has a 25% chance of having pathological mutations in LAL genes from both their mother and their father, a 50% chance of having a pathological mutation in only one gene, and a 25% chance of having no pathological mutations. Genetic testing for family members and genetic prenatal diagnosis of pregnancies for women who are at increased risk are possible if family members carrying pathological mutations have been identified.

In terms of the diagnosis for glycogen storage disease type III, the following tests/exams are carried out to determine if the individual has the condition:

- Biopsy (muscle or liver)

- CBC

- Ultrasound

- DNA mutation analysis (helps ascertain GSD III subtype)

The differential diagnosis of glycogen storage disease type III includes GSD I, GSD IX and GSD VI. This however does not mean other glycogen storage diseases should not be distinguished as well.

No specific cure has been discovered for homocystinuria; however, many people are treated using high doses of vitamin B (also known as pyridoxine). Slightly less than 50% respond to this treatment and need to take supplemental vitamin B for the rest of their lives. Those who do not respond require a Low-sulfur diet (especially monitoring methionine), and most will need treatment with trimethylglycine. A normal dose of folic acid supplement and occasionally adding cysteine to the diet can be helpful, as glutathione is synthesized from cysteine (so adding cysteine can be important to reduce oxidative stress).

Betaine (N,N,N-trimethylglycine) is used to reduce concentrations of homocysteine by promoting the conversion of homocysteine back to methionine, i.e., increasing flux through the re-methylation pathway independent of folate derivatives (which is mainly active in the liver and in the kidneys).The re-formed methionine is then gradually removed by incorporation into body protein. The methionine that is not converted into protein is converted to S-adenosyl-methionine which goes on to form homocysteine again. Betaine is, therefore, only effective if the quantity of methionine to be removed is small. Hence treatment includes both betaine and a diet low in methionine. In classical homocystinuria (CBS, or cystathione beta synthase deficiency), the plasma methionine level usually increases above the normal range of 30 micromoles/L and the concentrations should be monitored as potentially toxic levels (more than 400 micromoles/L) may be reached.

Pyruvate dehydrogenase deficiency can be diagnosed via the following methods:

- Blood test (Lactate and pyruvate levels)

- Urine analysis

- Magnetic resonance spectroscopy

- MRI

The differential diagnosis of pyruvate dehydrogenase deficiency can consist of either D-Lactic acidosis or abnormalities associated with gluconeogenesis.

LAL deficiency can be treated with sebelipase alfa is a recombinant form of LAL that was approved in 2015 in the US and EU. The disease of LAL affects < 0.2 in 10,000 people in the EU. According to an estimate by a Barclays analyst, the drug will be priced at about US $375,000 per year.

It is administered once a week via intraveneous infusion in people with rapidly progressing disease in the first six months of life. In people with less aggressive disease, it is given every other week.

Before the drug was approved, treatment of infants was mainly focused on reducing specific complications and was provided in specialized centers. Specific interventions for infants included changing from breast or normal bottle formula to a specialized low fat formula, intravenous feeding, antibiotics for infections, and steroid replacement therapy because of concerns about adrenal function.

Statins were used in people with LAL-D prior to the approval of sebelipase alfa; they helped control cholesterol but did not appear to slow liver damage; liver transplantation was necessary in most patients.

There is no cure for GALT deficiency, in the most severely affected patients, treatment involves a galactose free diet for life. Early identification and implementation of a modified diet greatly improves the outcome for patients. The extent of residual GALT enzyme activity determines the degree of dietary restriction. Patients with higher levels of residual enzyme activity can typically tolerate higher levels of galactose in their diets. As patients get older, dietary restriction is often relaxed. With the increased identification of patients and their improving outcomes, the management of patients with galactosemia in adulthood is still being understood.

After diagnosis, patients are often supplemented with calcium and vitamin D3. Long-term manifestations of the disease including ovarian failure in females, ataxia. and growth delays are not fully understood. Routine monitoring of patients with GALT deficiency includes determining metabolite levels (galactose 1-phosphate in red blood cells and galactitol in urine) to measure the effectiveness of and adherence to dietary therapy, ophthalmologic examination for the detection of cataracts and assessment of speech, with the possibility of speech therapy if developmental verbal dyspraxia is evident.

The initial workup of abetalipoproteinemia typically consists of stool sampling, a blood smear, and a fasting lipid panel though these tests are not confirmatory. As the disease is rare, though a genetics test is necessary for diagnosis, it is generally not done initially.

Acanthocytes are seen on blood smear. Since there is no or little assimilation of chylomicrons, their levels in plasma remains low.

The inability to absorb fat in the ileum will result in steatorrhea, or fat in the stool. As a result, this can be clinically diagnosed when foul-smelling stool is encountered. Low levels of plasma chylomicron are also characteristic.

There is an absence of apolipoprotein B. On intestinal biopsy, vacuoles containing lipids are seen in enterocytes. This disorder may also result in fat accumulation in the liver (hepatic steatosis). Because the epithelial cells of the bowel lack the ability to place fats into chylomicrons, lipids accumulate at the surface of the cell, crowding the functions that are necessary for proper absorption.

In terms of the diagnosis of adenylosuccinate lyase deficiency one should look for (or exam/method):

- MRI

- Demonstration of Succinylpurines in extracellular fluids like plasma, cerebrospinal fluid (CSF) and/or urine using HPLC or HPLC-MS

- Genetic testing - genomic cDNA sequencing of the ADSL gene and characterization of mutant proteins.

The majority of patients is initially screened by enzyme assay, which is the most efficient method to arrive at a definitive diagnosis. In some families where the disease-causing mutations are known and in certain genetic isolates, mutation analysis may be performed. In addition, after a diagnosis is made by biochemical means, mutation analysis may be performed for certain disorders.

The official recommendation from the United States Preventive Services Task Force is that for persons that do not fall within an at-risk population and are asymptomatic, there is not enough evidence to prove that there is any benefit in screening for vitamin D deficiency.

The National Institutes of Health has found that "Large amounts of folic acid can mask the damaging effects of vitamin B deficiency by correcting the megaloblastic anemia caused by vitamin B deficiency without correcting the neurological damage that also occurs", there are also indications that "high serum folate levels might not only mask vitamin B deficiency, but could also exacerbate the anemia and worsen the cognitive symptoms associated with vitamin B deficiency". Due to the fact that in the United States legislation has required enriched flour to contain folic acid to reduce cases of fetal neural-tube defects, consumers may be ingesting more than they realize. To counter the masking effect of B deficiency the NIH recommends "folic acid intake from fortified food and supplements should not exceed 1,000 μg daily in healthy adults." Most importantly, B deficiency needs to be treated with B repletion. Limiting folic acid will not counter the irrevocable neurological damage that is caused by untreated B deficiency.

Serum B levels are often low in B deficiency, but if other features of B deficiency are present with normal B then further investigation is warranted. One possible explanation for normal B levels in B deficiency is antibody interference in people with high titres of intrinsic factor antibody.

Some researchers propose that the current standard norms of vitamin B levels are too low.

One Japanese study states the normal limits as 500–1,300 pg/mL. Range of vitamin B12 levels in humans is considered as normal: >300 pg/mL; moderate deficiency: 201–300 pg/mL; and severe deficiency: <201 pg/mL.

Serum vitamin B tests results are in pg/mL (picograms/milliliter) or pmol/L (picomoles/liter). The laboratory reference ranges for these units are similar, since the molecular weight of B is approximately 1000, the difference between mL and L. Thus: 550 pg/mL = 400 pmol/L.

Serum homocysteine and methylmalonic acid levels are considered more reliable indicators of B deficiency than the concentration of B in blood. The levels of these substances are high in B deficiency and can be helpful if the diagnosis is unclear.

Routine monitoring of methylmalonic acid levels in urine is an option for people who may not be getting enough dietary B, as a rise in methylmalonic acid levels may be an early indication of deficiency.

If nervous system damage is suspected, B analysis in cerebrospinal fluid is possible, though such an invasive test should be considered only if blood testing is inconclusive.

The Schilling test has been largely supplanted by tests for antiparietal cell and intrinsic factor antibodies.

The serum concentration of 25(OH)D is typically used to determine vitamin D status. Most vitamin D is converted to 25(OH)D in the serum, giving an accurate picture of vitamin D status.

The level of serum 1,25(OH)D is not usually used to determine vitamin D status because it often is regulated by other hormones in the body such as parathyroid hormone. The levels of 1,25(OH)D can remain normal even when a person may be vitamin D deficient.

Serum level of 25(OH)D is the laboratory test ordered to indicate whether or not a person has vitamin D deficiency or insufficiency.

It is also considered reasonable to treat at-risk persons with vitamin D supplementation without checking the level of 25(OH)D in the serum, as vitamin D toxicity has only been rarely reported to occur.

Levels of 25(OH)D that are consistently above 200 ng/mL (500 nmol/L) are thought to be potentially toxic, although data from humans are sparse. Vitamin D toxicity usually results from taking supplements in excess. Hypercalcemia is often the cause of symptoms, and levels of 25(OH)D above 150 ng/mL (375 nmol/L) are usually found, although in some cases 25(OH)D levels may appear to be normal. Periodic measurement of serum calcium in individuals receiving large doses of vitamin D is recommended.

If treatment is initiated early in disease the neurologic sequelae may be reversed and further deterioration can be prevented.

Treatment of adenylosuccinate lyase deficiency can be done via epilepsy management with anticonvulsive drugs.Additionally the following options include:

- D-ribose and uridine administration

- Ketogenic diet

- S-adenosyl-l-methionine

The symptoms of LSD vary, depending on the particular disorder and other variables such as the age of onset, and can be mild to severe. They can include developmental delay, movement disorders, seizures, dementia, deafness, and/or blindness. Some people with LSDhave enlarged livers (hepatomegaly) and enlarged spleens (splenomegaly), pulmonary and cardiac problems, and bones that grow abnormally.

Familial LPL deficiency should be considered in anyone with severe hypertriglyceridemia and the chylomicronemia syndrome. The absence of secondary causes of severe hypertriglyceridemia (like e.g. diabetes, alcohol, estrogen-, glucocorticoid-, antidepressant- or isotretinoin-therapy, certain antihypertensive agents, and paraproteinemic disorders) increases the possibility of LPL deficiency. In this instance besides LPL also other loss-of-function mutations in genes that regulate catabolism of triglyceride-rich lipoproteins (like e.g. ApoC2, ApoA5, LMF-1, GPIHBP-1 and GPD1) should also be considered

The diagnosis of familial lipoprotein lipase deficiency is finally confirmed by detection of either homozygous or compound heterozygous pathogenic gene variants in "LPL" with either low or absent lipoprotein lipase enzyme activity.

Lipid measurements

· Milky, lipemic plasma revealing severe hyperchylomicronemia;

· Severely elevated fasting plasma triglycerides (>2000 mg/dL);

LPL enzyme

· Low or absent LPL activity in post-heparin plasma;

· LPL mass level reduced or absent in post-heparin plasma;

Molecular genetic testing

The LPL gene is located on the short (p) arm of chromosome 8 at position 22. More than 220 mutations in the LPL gene have been found to cause familial lipoprotein lipase deficiency so far.