Diagnostic Testing for Scabies in Canterbury

The diagnosis of scabies is usually made clinically, as although laboratory testing can be performed by taking scrapings from the suspicious looking area of skin, this has very poor sensitivity.

Like other regions in New Zealand, the positivity rate for scabies laboratory examination is very low in Canterbury, at < 10% of all collections. This can be due to multiple factors, including experience of the examiner, pre-treatment of the patient, absence of scabies on the patient or too few mites on a patient making them difficult to find.

As such, from Monday 10th February 2020, skin scrapings for Scabies will only be performed following a discussion of the primary care doctor with a clinical microbiologist. If the clinical microbiologist supports a scraping please note the name of the microbiologist on the request form and ask the patient to make an appointment with the laboratory.

Where there is no evidence of a discussion with a clinical microbiologist included on the request form the on call clinical microbiologist will review the request form and makes a decision regarding processing.

Health Pathways contains information regarding diagnosis and testing which are included below.

  • Diagnosis is usually clinical. See DermNet NZ – Scabies for useful images
  • Testing on skin scrapings has poor sensitivity

Refer for testing, as below, recognising low sensitivity, if:

  • unclear diagnosis
  • failed appropriate treatment. If possible, refer at least 2 weeks after last scabies
  • treatment attempt
  • possible infestation in vulnerable community, e.g. rest home

For any queries, please contact:

Discontinuation of Reporting Anti-thyroglobulin as part of the Thyroid Antibody Screen

From Monday 10th February 2020 Canterbury SCL (CSCL) and Canterbury Health Laboratories (CHL) will no longer report anti-thyroglobulin (anti-Tg) as part of the routine thyroid antibody screen.

Given the superior clinical utility of anti‐thyroid microsomal (anti‐TPO) antibodies, when thyroid antibodies are ordered the laboratory will perform anti‐thyroid microsomal (anti‐TPO) antibodies only.

The most common cause of thyroid dysfunction is autoimmunity, with autoimmune thyroid disease the most common autoimmune condition in our community. Thyroid related autoantibodies are useful in supporting autoimmunity as the underlying mechanism, particularly where the cause of abnormal thyroid function tests is unclear. In patients with hypothyroidism, anti‐thyroid microsomal or peroxidase antibodies (anti‐TPO) is the more specific and helpful autoantibody to order when autoimmune
(Hashimoto’s) thyroiditis is suspected. However, like many autoantibodies, it can be detected in many patients years before the onset of clinically overt hypothyroidism.

Although commonly ordered, anti‐thyroglobulin (anti-Tg) antibodies are less specific for the diagnosis of autoimmune thyroid disease.

Measurement of thyroglobulin (Tg) is used to monitor patients with differentiated thyroid cancer. However, the presence of anti-Tg antibodies in these patients can interfere with the measurement of Tg. For this reason, anti-Tg will continue to be measured at the same time as Tg in these
patients. When Tg is requested, the anti-Tg test is always added automatically and there is no requirement to specify a request for anti-Tg on the request form.

For any queries, please contact: