Reference intervals for deconjugated urine metanephrines by Bhattacharya analysis

BACKGROUND

Urine metanephrines are used to screen for phaeochromocytoma or paraganglioma (PPGL). Current reference intervals (RI) derived in healthy individuals are not age or sex-stratified, and lower than in hypertensive patients, leading to high false positive rates. This study aims to determine age and sex-stratified RI from a contingent screening population.

METHODS

Patients with 24-h deconjugated urine metanephrines from 3/6/2010 to 27/8/2022 were included (2936 males, 5285 females), initially by liquid chromatography-electrochemical detection (LC-ECD) then liquid chromatography-tandem mass spectrometry (LC-MS/MS). Bhattacharya analysis was used after log transformation to determine age and sex-stratified RI for metanephrine excretion, normetanephrine excretion, metanephrine/creatinine and normetanephrine/creatinine ratios.

RESULTS

Normetanephrine excretion increases with age (RI: males: 18-<30 years: <3.4 µmol/24 h, 30-<40 years: <3.7 µmol/24 h, 40+ years: <5.3 µmol/24 h; females: 18-<30 years: <2.7 µmol/24 h, 30-<40 years: <3.1 µmol/24 h, 40+ years: <3.7 µmol/24 h), while metanephrine excretion was consistent across adulthood (RI: males: 18+ years: <1.8 µmol/24 h; females: 18+ years: <1.2 µmol/24 h). However, normetanephrine/creatinine and metanephrine/creatinine increase steadily with age after early adulthood, likely due to a decrease in muscle mass, with females having higher normetanephrine/creatinine and metanephrine/creatinine ratios.

CONCLUSIONS

Age and sex-stratified RI were derived for metanephrine excretion, normetanephrine excretion, metanephrine/creatinine and normetanephrine/creatinine ratios. This is expected to reduce false positives while flagging most PPGL.

Dual porphyria with mutations in both the UROD and HMBS genes

The porphyrias are a group of inborn or acquired disorders of haem synthesis that can result in neurovisceral or dermatological symptoms. Diagnosis is usually made using a combination of clinical presentation and biochemical parameters. This case report describes a 25-year-old woman clinically presenting with a rash and then found to have elevated porphobilinogen concentrations in her urine. The initial presumptive diagnosis of variegate porphyria was not supported by analysis of her plasma, urine and faeces, which suggested a combination of acute intermittent porphyria and porphyria cutanea tarda. Sequencing of the hydroxymethylbilane synthase and uroporphyrinogen decarboxylase genes confirmed the relatively rare diagnosis of dual porphyria, and revealed a novel uroporphyrinogen decarboxylase mutation.

Clinical indications for the investigation of porphyria: case examples and evolving laboratory approaches to its diagnosis in New Zealand

Patients with porphyria present in a diverse and unusual variety of ways and most clinicians will see only a few cases, if any, during their professional lives. Porphyria may present (1) with acute symptoms, which may be abdominal pain, neurological or psychiatric; (2) with skin rash or photosensitivity; or (3) with a putative family history. Screening for latent porphyria has been greatly facilitated by fluorescence emission scanning of plasma and by mutational analysis. Our reference laboratory has recently diagnosed several cases of the less common types of porphyria, which we postulate is due to the availability of these methods and to the changing population of New Zealand. Accurate screening and diagnosis of porphyria is important, as an acute porphyric attack is life-threatening and preventable. Retrospective diagnosis may be difficult.

Measurement of thiopurine methyl transferase activity guides dose-initiation and prevents toxicity from azathioprine

AIM

To establish an assay service for thiopurine methyl transferase (TPMT) activity in order to facilitate dose initiation of thiopurine drug therapy and to define appropriate reference intervals and optimal cut-offs for the New Zealand population.

METHODS

407 patients underwent radio-enzymatic assay testing of TPMT activity prior to initiation of thiopurine drug therapy. Those with low activity also underwent genotyping for the abnormal *2, *3A, and *3C alleles.

RESULTS

A trimodal distribution of enzyme activity was seen consistent with the known polymorphic genetics for this enzyme. Three cases of homozygous deficiency were identified. The 'normal' range is 9.3 to 17.6 units/ml red blood cells (RBCs), but many heterozygotes have activity above the lower limit of his range. TPMT activity above 10.7 units/ml RBC identifies a normal genotype with 100% probability.

CONCLUSION

The normal range for TPMT has been established. The measurement of TPMT activity helps to guide dose initiation and may prevent toxicity from azathioprine.

[Debit and credit. Menopause between illusion and reality]

Middle-aged women in patriarchial societies are still widely considered as deficient and damaged and therefore can easily become objects of medical attention. The authors seek the reasons for this in fact that the different changes of male and female potency in the 45 to 55 age-group provoke defense mechanisms. These are meant to ensure the intactness of the male--who then is supposedly in his 'best age'--for the sake of both men and women. Apart from this, psychoanalytical theories--like the one of the "depressive position", held by Melanie Klein--confirm the prejudice that a woman going through the change of life is damaged, and thus has to mourn the "desease" of menopause.