Vitamin D-binding protein as it is understood in 2016: is it a critical key with which to help to solve the calcitriol conundrum?

Background The misnamed 'vitamin' D is actually the hormone calcitriol (1,25 dihydroxyhydroxyvitamin D). It has a central regulatory role in calcium metabolism, and more widely in the immune system. The prohormone calcifediol (25 hydroxyvitamin D) is more easily measured in the laboratory and is the analyte used in reference interval formulation. Being highly lipid soluble, both calcifediol and calcitriol travel in the bloodstream on carriage proteins, principally on vitamin D-binding protein. Summary This review reports our current understanding of vitamin D-binding protein. Its genetic determinants and their effect on it and secondarily on calcifediol concentrations and assays are described. Its complex interplay with parathyroid hormone is considered. The analytical state of the art is translated into the challenge it imposes clinically, in the formulation of reference intervals and in their use in advising and managing patients. Several recent challenges thrown up to laboratories by percipient clinicians highlight the dilemma vitamin D-binding protein poses. A way forward is suggested.

Potential health promotion benefits of lipid testing for all patients presenting with chest pain to an emergency department

OBJECTIVES

To establish the prevalence of previously undiagnosed dyslipidaemia in patients presenting to the emergency department (ED) with non-traumatic chest pain and, more particularly, the prevalence in the subgroup which was discharged home from the ED, the group that traditionally would not have received a lipid test.

METHODS

Prospective, observational study of adult patients presenting to an ED with non-traumatic chest pain as the presenting complaint.

RESULTS

A total of 185 eligible patients underwent lipid testing during their presentation: 96 in the ED and 89 in the wards. Overall 61% (n = 112) of patients had at least one abnormal lipid level. Of patients discharged from the ED, 62% had at least one abnormal lipid level.

CONCLUSIONS

A moderate, but useful, increase in detection rates of dyslipidaemia is possible if lipid testing is offered to all patients presenting with chest pain, and not just to those who are admitted to wards for further investigation and management of suspected acute coronary syndromes. Testing of this group should be considered as a health promotion initiative in the ED, with appropriate follow up in the community.

Selective versus universal screening for gestational diabetes mellitus: an evaluation of predictive risk factors

OBJECTIVE

To assess whether selective screening for gestational diabetes mellitus (GDM) on the basis of risk-factor assessment is a practicable alternative to universal screening.

DESIGN

Case-control study.

SETTING

A 212-bed regional specialist hospital in Melbourne, providing services in obstetrics and gynaecology, paediatrics, geriatrics and rehabilitation.

SUBJECTS

6,032 women who gave birth at the hospital, May 1996 to August 1997 and November 1997 to August 1998; all were screened for GDM, and 313 were diagnosed with the condition.

MAIN OUTCOME MEASURES

Odds ratios (ORs) for risk factors (age, obesity, family history of diabetes mellitus and high-risk racial heritage) in women with GDM compared to those without GDM; proportion of women with GDM whose diagnosis would have been missed by selective screening.

RESULTS

ORs were 1.9 for age > or = 25 years (95% CI, 1.3-2.7), 2.3 for body mass index > or = 27kg/m2 (95% CI, 1.6-3.3), 2.5 for high-risk racial heritage (95% CI, 2.0-3.2), and 7.1 for family history of diabetes mellitus (95% CI, 5.6-8.9). Other proposed criteria (previous GDM and glycosuria) added no further diagnostic power. Selective screening using the above four criteria would have missed two of 313 cases (0.6%) and could have saved screening up to 1,025 women without GDM (17% of all women).

CONCLUSIONS

Selective screening for GDM based on prior risk assessment can reduce the need for testing, with negligible loss of diagnostic efficiency.

Thyroid function testing based on assay of thyroid-stimulating hormone: assessing an algorithm's reliability

OBJECTIVE

To assess the ability of an algorithm for thyroid-function testing (based on assay of thyroid-stimulating hormone [TSH]) to discern euthyroidism in patients with and without conditions affecting thyroid function.

DESIGN

The Australian Health Insurance Commission (HIC) specifies clinical categories for which Medicare rebate is given for assay of both TSH and free thyroxine (FT4), but otherwise rebates for thyroid function testing are given for TSH assay only. A prospective study was made of paired TSH and FT4 results of 1000 consecutive assays categorised by indication for testing. An FT4 value within the reference range was accepted as indicating euthyroidism; the reliability of an initial TSH measurement as the sole indicator of thyroid disease was assessed against this criterion standard.

SETTING

A large suburban teaching hospital.

OUTCOME MEASURE

Success or failure of the algorithm, with failure defined as an abnormal FT4 level missed because the TSH level was normal.

RESULTS

The algorithm failure rate both overall and in the patients not in the HIC clinical categories was 2.7%, and there was no significant difference in algorithm failure rate in the patients in the various HIC clinical categories. The categories and failure rates were: patients being monitored for thyroid disease, 3.4%; patients with the "sick euthyroid" syndrome, nil; patients with psychosis or dementia, 1.1%; patients taking drugs affecting thyroid function, 2.1%; and patients with pituitary dysfunction, one of six cases. The range of FT4 values in patients in whom the algorithm failed was 6.4-29.5 pmol/L in those without thyroid disease and 3.4-27.4 pmol/L in those with thyroid disease. In patients being monitored for thyroid disease, the proportion of abnormal values of TSH alone was significant (P<0.001).

CONCLUSION

We have shown that the HIC's imposition of a TSH-based algorithm by financial fiat is also scientifically acceptable. Use of this algorithm in hospitals (including psychiatric hospitals) will result in substantial savings.