Oral glucose tolerance test to diagnose gestational diabetes mellitus: Impact of variations in specimen handling.

To improve birth outcomes, all pregnant women without known diabetes are recommended for an oral glucose tolerance test (OGTT) to screen for hyperglycaemia in pregnancy (diabetes in pregnancy or gestational diabetes mellitus (GDM)). This narrative review presents contemporary approaches to minimise preanalytical glycolysis in OGTT samples with a focus on GDM diagnosis using criteria derived from the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study. The challenges of implementing each approach across a diverse Australian healthcare setting were explored. Many Australian sites currently collect and transport OGTT samples at ambient temperature in sodium fluoride (NaF) tubes which is likely to lead to missed diagnosis of GDM in a significant proportion of cases. Alternative preanalytical solutions should be pragmatic and tailored to individual settings and as close as possible to the preanalytical conditions of the HAPO study for correct interpretation of OGTT results. Rapid centrifugation of barrier tubes to separate plasma could be suitable in urban settings provided time to centrifugation is strictly controlled. Tubes containing NaF and citrate could be useful for remote or resource poor settings with long delays to analysis but the impact on the interpretation of OGTT results should be carefully considered. Testing venous blood glucose at the point-of-care bypasses the need for glycolytic inhibition but requires careful selection of devices with robust analytical performance. Studies to evaluate the potential error of each solution compared to the HAPO protocol are required to assess the magnitude of misdiagnosis and inform clinicians regarding the potential impact on patient safety and healthcare costs.

Assessment of analytical bias in ferritin assays and impact on functional reference limits.

Serum ferritin is currently the recommended laboratory test to investigate iron deficiency. There have been efforts to standardise serum ferritin assays with implementation of traceability to the World Health Organization reference standard. We evaluate the analytical bias among five widely used commercial ferritin assays in Australia. The relationship between serum ferritin and erythrocyte parameters was recently explored to derive functional reference limits. Residual patient serum specimens were analysed by five participating laboratories that utilised a different ferritin assay, Abbott, Beckman Coulter, Roche, Siemens, and Ortho. Using data mining approach, functional reference limits for Siemens, Abbott, and Ortho serum ferritin methods were derived and compared. At clinically relevant ferritin decision points, compared to the Beckman method, the Roche assay showed higher results ranging from 6 µg/L (31%) at the lowest decision point to 575 µg/L (57%) at the highest decision point. In contrast, the Ortho method underestimated ferritin results at lower decision points of 20 and 30 µg/L, with estimated ferritin results of 16 µg/L (-19%) and 27 µg/L (-12%), respectively. The Abbott and Siemens assays showed a positive bias which was introduced at differing decision points. The comparison of the Siemens and Ortho methods presents similar inflection points between the two assays in the establishment of functional reference limits for serum ferritin. There remain significant biases among some of the commonly used commercial ferritin assays in Australia. More studies are needed to assess if functional reference limits are a way to overcome method commutability issues.

Routine free thyroxine reference intervals are suboptimal for monitoring children on thyroxine replacement therapy and target intervals need to be assay-specific.

Central hypothyroidism is a condition where there is (qualitatively or quantitatively) TSH deficiency, leading to reduced thyroid hormone production. In such patients, serum TSH does not accurately reflect the adequacy of thyroxine replacement, as the log-linear relationship between thyrotropin (TSH) and free thyroxine (FT4) is lost. We aimed to prospectively determine the optimal physiological FT4 treatment range for children treated for primary hypothyroidism, based on their serum TSH concentrations. This information could be used to guide optimal therapy for all children on thyroxine replacement, including those with central hypothyroidism. In total, sixty children (median age: 11 years, range: 11 months to 18 years) were recruited over 21 months. They were prescribed a stable dose of thyroxine for at least 6-8 weeks prior to a thyroid function test that consisted of serum TSH, FT4 and free triiodothyronine (FT3) measurements. The serum sample for the thyroid function tests was collected before ingestion of the daily dose, i.e. the trough concentration, and measured using Beckman Coulter UniCel DxI 800 instrument, Siemens Advia Centaur, Roche Cobas, Abbott Architect, Ortho Clinical Diagnostics Vitros 5600 (Ortho-Clinical Diagnostics, Raritan, NJ) platforms. The FT4 and FT3 reference intervals showed significant inter-method difference. The lower limit of the FT4 reference intervals were generally shifted mildly higher when the TSH concentration of the children were restricted from 0.5-5.0 mIU/L to 0.5-2.5 mIU/L. By contrast, the upper limit of the FT3 and FT4 reference intervals were relatively stable for the different TSH concentrations. Assay-specific target ranges for optimal thyroxine therapy are required until FT4 assay standardisation is realised.

Difficulties in cerebrospinal fluid ßhCG interpretation in a patient with an infundibular lesion.

A variety of neoplastic, inflammatory and congenital conditions can cause pituitary stalk thickening. Differentiating between these causes is important as targeted treatment may be offered. Diagnostic work-up consists of a thorough history, examination, biochemical analysis and imaging. We present the case of a 33-year-old male who presented with diabetes insipidus and had pituitary stalk thickening on magnetic resonance imaging. Further investigations revealed an elevated CSF ßhCG, which raised the possibility of an intracranial germ cell tumor. However, when repeated on four different assays, the ßhCG levels were discordant. On serial imaging, the pituitary stalk thickening reduced slightly, which would be unexpected for a germ cell tumor. This case raises the difficulties interpreting CSF ßhCG, as not all immunoassays for ßhCG have been validated for use in CSF. The Roche Diagnostics Elecsys and Siemens Centaur assays have been validated for CSF ßhCG, and so we advocate using one of these methods. If unavailable or serum/CSF results are ambiguous, serial MRI is appropriate, with pituitary stalk biopsy considered if the stalk measures >6.5 mm or other imaging abnormalities are present. LEARNING POINTS: Most adult patients with central diabetes insipidus have imaging abnormalities on a pituitary MRI. The most common abnormalities are loss of the posterior pituitary bright spot and pituitary stalk thickening, both of which are non-specific.Causes of pituitary stalk thickening include neoplastic, inflammatory, infective and congenital lesions.Investigation of pituitary stalk thickening should encompass the many possible causes and include biochemical analyses as well as imaging of the chest, abdomen and pelvis. Further investigations should be guided by the clinical context, but may include testicular ultrasound, CSF analysis and pituitary stalk biopsy.Germ cell tumors involving the pituitary stalk may be suspected on clinical grounds, but in the absence of a tissue diagnosis (biopsy) confirmation may be difficult and relies on biochemical assessment of blood and possibly CSF as well as serial MRI imaging.CSF ßhCG levels should be analyzed on an instrument validated for use in CSF or on multiple instruments, and the pitfalls of testing this marker (false negative in some germ cell tumors, false positives in other conditions, lack of internationally agreed reference ranges for diagnosing germ cell tumors) should be considered when interpreting the results.

Reporting Thyroid Function Tests in Pregnancy.

While there is agreement that overt maternal hypothyroidism (serum thyroid stimulating hormone (TSH) >10 mIU/L) should be treated immediately, the evidence is mixed regarding the harm associated with subclinical hypothyroidism and the benefits of thyroxine replacement. The diagnosis of subclinical hypothyroidism rests on the recognition of an increased serum concentration of TSH which may be affected by many factors including gestational age, analytical method, the antibody status of the mother, ethnicity, iodine nutrition and even the time of day when the blood is collected. The 97.5(th) percentile of TSH at the end of the first trimester is commonly used as the upper boundary of normal in early pregnancy with a default value of 2.5 mIU/L specified in a number of recent clinical guidelines. There have now been numerous papers showing that a more realistic figure is between 3.0 and 4.0 mIU/L depending on the analytical method that is used. There are suggestions that ethnicity may also have a significant effect on TSH and FT4 reference limits in pregnancy.

Poor readers' use of orthographic information in learning to read new words: a visual bias or a phonological deficit?

In this study, we examined the ability of 11-year-old poor readers and reading age controls to learn new print vocabulary. It was found that the poor readers were slower than the controls to learn to read a set of nonwords accurately but that, when asked to pick out the nonwords in a visual recognition memory task, they reached criterion much more quickly than did the controls. However, when the groups were compared on auditory recall of the items being learned, the poor readers were at a disadvantage. Thus, the poor readers developed a visual store for the nonwords more quickly than did the controls but were slower to establish phonological representations for the nonwords. It was concluded that the poor readers were slower to establish a form of sight word reading that was well underpinned in memory by connections between the letters in the spelling and the phonemes in the pronunciation, suggesting that they had a greater reliance on an orthographic-semantic pathway in word recognition than did the controls.

Recommendations for lipid testing and reporting by Australian pathology laboratories.

The importance of measuring blood lipids in determining the absolute risk of a cardiovascular event is now well established. In Australia, the National Heart Foundation of Australia and the Cardiac Society of Australia and New Zealand (NHFA/CSANZ) have done much to educate doctors. In recent years the recommendations of the NHFA/CSANZ have been based on values for Low-density lipoprotein (LDL-C) as well as High-density lipoprotein cholesterol (HDL-C) and Triglyceride (TG). This change has been reflected in requests to pathology laboratories. However the interpretation of these results may be difficult and the NHFA guidelines outline desirable values for patients at high risk only. There are no formal recommendations for reference intervals or interpretive comments. With the availability of expert systems, some pathology laboratories are now in a better position to provide specific comments to assist with the interpretation of test results. An ad hoc committee of private and public chemical pathologists met to draft recommendations for lipid testing and reporting by Australian pathology providers, on the basis of current guidelines and their own expertise. Provisions in the current Medicare Benefits Schedule (MBS) for lipid testing were reviewed, and the indications for lipid testing, recommended tests, the logistics of managing specimens, methods of analysis and availability of specialised tests have been documented. Recommendations are made on the provision of desirable values for lipid tests. Suggestions are provided on interpretive comments which could accompany reports of lipid test results, including categorisation of the likely associated lipoprotein abnormalities, their causes, contribution to risk for cardiovascular disease (CVD) and targets for treatment. Current and future approaches to the assessment of risk for CVD are discussed.

The trouble with Troponin.

Serum Troponin is a sensitive and specific marker of heart muscle damage that is widely used in the assessment of people with chest pain. Its usefulness is, however, sometimes limited by false positive or negative results caused by proteins or fibrin in the patient's blood. More importantly, there is no agreed Troponin I standard at present which means that results from different assays cannot be directly compared. In addition, there is no consensus of the way in which serum Troponin results should be reported which means that some cut-offs minimise false positives, whilst others minimise false negatives. There is a need for cardiologists and pathologists to work together to resolve this issue.

Repetition learning in the immediate serial recall of visual and auditory materials.

In 5 experiments, a Hebb repetition effect, that is, improved immediate serial recall of an (unannounced) repeating list, was demonstrated in the immediate serial recall of visual materials, even when use of phonological short-term memory was blocked by concurrent articulation. The learning of a repeatedly presented letter list in one modality (auditory or visual) did not transfer to give improved performance on the same list in the other modality. This result was not replicated for word lists, however, for which asymmetric transfer was observed. Inferences are made about the structure of short-term memory and about the nature of the Hebb repetition effect.

Expression of the noradrenaline transporter and phenylethanolamine N-methyltransferase in normal human adrenal gland and phaeochromocytoma.

Expression of the noradrenaline transporter (NAT) was examined in normal human adrenal medulla and phaeochromocytoma by using immunohistochemistry and confocal microscopy. The enzymes tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) were used as catecholamine biosynthetic markers and chromogranin A (CGA) as a marker for secretory granules. Catecholamine content was measured by using high performance liquid chromatography (HPLC). In normal human adrenal medulla (n=5), all chromaffin cells demonstrated strong TH, PNMT and NAT immunoreactivity. NAT was co-localized with PNMT and was located within the cytoplasm with a punctate appearance. Human phaeochromocytomas demonstrated strong TH expression (n=20 samples tested) but variable NAT and PNMT expression (n=24). NAT immunoreactivity ranged from absent (n=3) to weak (n=10) and strong (n=11) and, in some cases, occupied an apparent nuclear location. Unlike the expression seen in normal human adrenal medullary tissue, NAT expression was not consistently co-localized with PNMT. PNMT also showed highly variable expression that was poorly correlated with tumour adrenaline content. Immunoreactivity for CGA was colocalized with NAT within the cytoplasm of normal human chromaffin cells (n=4). This co-localization was not consistent in phaeochromocytoma tumour cells (n=7). The altered pattern of expression for both NAT and PNMT in phaeochromocytoma indicates a significant disruption in the regulation and possibly in the function of these proteins in adrenal medullary tumours.

Word length, phonemic, and visual similarity effects in poor and normal readers.

Serial order recall for visually and auditorily presented stimuli was examined in a group of 12-year-old poor readers and 7-year-old reading-age controls. With pictorial presentation, the poor readers showed a visual similarity effect, no word length effect, and a smaller phonemic similarity effect than that of controls. However, with visual presentation of printed words and with auditory presentation, poor readers showed word length and phonemic similarity effects of similar magnitude to that of controls. It is concluded that poor readers rely on visual information in tasks where the presented images are highly codable, and where verbal recoding is not obligatory, but that they will make use of phonological coding when the stimuli are not as easily codable visually in memory.