Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
Measurement of 7-dehydrocholesterol, desmosterol and lathosterol in plasma by GC-MS is performed to investigate rare inherited metabolic disorders of cholesterol synthesis. Smith-Lemli-Opitz syndrome (SLOS) is caused by deficiency of 7-dehyrocholesterol reductase and results in grossly elevated plasma 7-dehydrocholesterol.
Patients present with a range of clinical features of varying severity including characteristic dysmorphic features, syndactyly of the second and third toes, congenital heart defects and growth retardation.
Desmosterolosis (desmosterol reductase deficiency) and lathosterolosis (sterol Δ5-desaturase deficiency) are extremely rare disorders diagnosed by finding elevated plasma desmosterol and lathosterol respectively. Very small numbers of cases have been described which have similar clinical features to SLOS.
Measurement of total cholesterol is a poor screening test for these disorders as levels may be within age-related reference ranges.
Specimen container paediatric:
Lithium heparin plasma
Specimen container adult:
Lithium heparin plasma
Minimum volume paediatric:
1 mL blood, 0.5 mL plasma
Minimum volume adult:
2 mL blood, 1 mL plasma
Special requirements:
Protect from light. Blood sample should be centrifuged on receipt in the laboratory and the plasma separated and frozen.If urgent sample analysis is required, please contact the laboratory to discuss.
Transport requirements:
NUTH users: send sample to the laboratory at ambient temperature, protected from light. External hospitals: send sample to the RVI frozen and protected from light.
Interpretation:
Patients with Smith-Lemli-Opitz syndrome typically have levels of 7-dehydrocholesterol over 100-fold greater than the reference range.
Significantly increased lathosterol or desmosterol is consistent with lathosterolosis or desmosterolosis respectively.
Measurement of the sterol/cholesterol ratio can improve the diagnostic specificity of the test.
Exposure to light may cause degradation of sterols. A diagnosis of SLOS, desmosterolosis or lathosterolosis should be confirmed by gene mutation analysis.
Reference ranges:
| Reference Ranges for Sterols in Plasma and Serum | |||
| Sterol | Adults (18 years and over) | Paediatrics (under 18 yrs) | Units |
| Cholesterol | 2500 – 7200 | 1900 – 4900 | µmol/L |
| 7-dehydrocholesterol | Less than 2.5 | Less than 1.0 | µmol/L |
| Lathosterol | Less than 12.3 | Less than 5.7 | µmol/L |
| Desmosterol | Less than 4.2 | Less than 4.3 | µmol/L |
| Reference Ranges for Sterol/Cholesterol ratios | |||
| Sterol ratio | Adults (18 years and over) | Paediatrics (under 18 yrs) | Units |
| 7-dehydrocholesterol/ cholesterol | Less than 0.40 | Less than 0.40 | µmol/mmol |
| Lathosterol/cholesterol | 0.25 – 2.65 | 0.24 – 1.92 | µmol/mmol |
| Desmosterol/cholesterol | 0.14 – 0.75 | 0.22 – 1.42 | µmol/mmol |
Other info:
Serum or EDTA plasma are also acceptable, but must be protected from light.