Specimen should be placed on ice immediately post collection. Serum or plasma must be removed from the clot, RBC or separator gel within 6 hours.
Sample stability:
-
4 days at 15-25 o C
-
4 weeks at 2-8 o C
-
10 months at -20 o C
Due to ongoing release of homocysteine from erythrocytes, plasma homocysteine increases by approximately 1umol/L/h in unseparated samples at room temperature.
This test may be vetted by a pathologist.
The clinical information for the test must be clearly written on the request form. If clinical information is not provided, or does not provide sufficient justification for the test, the test may be declined.
Declined tests :
If a test is declined, the specimen will be held for a reasonable period (usually 3 weeks but dependant on the stability of the sample). Medical practitioners seeking approval for a declined test should email the on-call Chemical Pathologist ( chemicalpathologist@adhb.govt.nz ) , giving the patient's name and NHI number and the clinical justification for the test. If unable to email, call the on-call Chemical Pathologist via Lablink (09-3078995) and identify yourself as a doctor.
SST is the preferred sample for community samples.
REFERENCE INTERVAL: 5 - 15 umol/L
Uncertainty of Measurement : 10%
Principle: Enzymatic
Reagents: Roche Homocysteine kit
Analyser: Cobas c502
Homocysteine tests may require pathologist approval
The procedure for obtaining pathologist approval may be found in this Test Guide under "pathologist"
Criteria for approval of homocysteine tests:
-
Diagnosis of genetic classical homocystinuria. Clinical details must appear on the request form e.g. "?homocystinuria" or "premature vascular disease" or "thrombotic tendency" or similar.
-
Requests from paediatricians, cardiologists, opthalmologists, haematologists, specialist lipid, metabolic or cardiovascular disease clinics will be approved.
-
Other cases will require discussion with a Labplus chemical pathologist
-
Repeat testing is not indicated except for monitoring established cases of classical homocystinuria.
Classical Homocystinuria
A genetic condition associated with premature vascular disease. Homocysteine levels are very high (> 50 umol/L)
Vitamin B12 and folate deficiency
Plasma homocysteine may be elevated in vitamin B12 or folate deficiency, or genetic defects of vitamin B12 processing or the folate pathway.
Measurement of urine methylmalonic acid may help distinguish these further.
Other Causes and Effects of Increased Homocysteine
Lesser degrees of hyperhomocysteinaemia are also associated with increased risk of cardiovascular disease and stroke. (The urine test for homocystine is inappropriate in this context).
However, homocysteine-lowering interventions (e.g. folate and vitamin B6 supplementation) do not modify cardiovascular risk, despite the fact that they lower homocyteine levels. This suggests that homocysteine does not have a causative role in vascular disease.
Routine homocyteine testing is not recommended as part of cardiovascular risk assessment.
The methionine-loading test is not performed by LabPlus.
References :
1. Assessing cardiovascular risk: what the experts think. Best Practice Journal (www.BPAC.org.nz) 10-21
2. Miller ER, 3rd, Juraschek S, Pastor-Barriuso R et al. Meta-analysis of folic acid supplementation trials on risk of cardiovascular disease and risk interaction with baseline homocysteine levels. Am J Cardiol;106:517-527
3. Marti-Carvajal AJ, Sola I, Lathyris D, Salanti G. Homocysteine lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev. 2009:CD006612
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Specimen should be placed on ice immediately post collection.
Serum or plasma must be removed from the clot, RBC or separator gel within 6 hours post collection.
Send at 2-8 0 C within 4 weeks of collection.
If stored greater then 4 weeks post collection sample must be sent frozen.