Introduction: Dopaminomas or dopamine-secreting pheochromocytomas are rare neuroendocrine tumors that frequently lack the classic paroxysmal symptoms of catecholamine excess (headache, sweating, palpitation). Diagnosing these tumors is exceptionally challenging when biochemical markers— specifically markedly elevated urinary dopamine—are interpreted in patients receiving exogenous Levodopa (L-DOPA) therapy, as the intake obscures clinical significance. Case: A 76-year-old male with ischemic heart disease, stage 4 chronic kidney disease, and new-onset hypertension was admitted for acute cholecystitis. Imaging studies incidentally revealed bilateral adrenal masses and demonstrated lipid-rich characteristics upon further evaluation with computed tomography (CT) adrenal washout. Biochemical evaluation revealed extreme elevations in 24-hour urinary dopamine (47,534 nmol/24 hours; normal <3,237) and 3-methoxytyramine (18.93 µmol/24 hours; normal <2.60), whereas downstream urinary noradrenaline (5.0 nmol/24 hours; normal 71.5–505.3), adrenaline (4.0 nmol/24 hours; normal 9.2–122.3), normetanephrine (0.22 µmol/24 hours; normal 0.88–2.88), and metanephrine (0.25 µmol/24 hours; normal 0.33–1.53) levels were all significantly below their respective reference ranges. The diagnosis was complicated by the patient’s concurrent use of L-DOPA/Benserazide for flupentixol-induced parkinsonism. L-DOPA is a direct precursor to dopamine; its administration can cause massive, false-positive elevations in urinary dopamine, mimicking a dopaminoma’s biochemical signature. However, the unique combination of profoundly high dopamine alongside suppressed downstream catecholamines and metanephrines suggested a true dopaminesecreting tumor—potentially secondary to dopamine beta-hydroxylase (DBH) deficiency—rather than drug interference. Conclusion This case illustrates the profound difficulty in diagnosing dopaminoma when exogenous L-DOPA therapy creates a near-identical biochemical profile. The diagnostic dilemma is further amplified by vague symptomatology, multiple comorbidities, and non-suggestive imaging. However, the finding of isolated dopamine hypersecretion with suppressed metanephrines serves as a critical clinical clue. This pattern points toward an intratumoral biosynthetic defect rather than drug interference. Clinicians must maintain a high index of suspicion and perform meticulous biochemical fractionation to identify these rare, dopamineisolated secreting tumors.
Dopamine ; Levodopa

Introduction: Macro-thyroid-stimulating hormone (macro-TSH) is a rare complex formed by monomeric TSH with anti-TSH autoantibodies. Macromolecules of TSH are not renally excreted due to its large size, leading to elevated TSH measurements without clinical consequences. This rare condition frequently mimics subclinical hypothyroidism, often leading to misdiagnosis and inappropriate levothyroxine therapy. Case: A 17-year-old female with major depressive disorder was biochemically diagnosed with subclinical hypothyroidism (TSH 39.06 mIU/L, free thyroxine 4 12.9 pmol/L, antithyroid peroxidase negative) and commenced on levothyroxine. Over 5 years, her TSH levels heavily fluctuated (0.48–82.59 mIU/L) and remained persistently elevated with high-normal free T4 levels despite treatment adherence. An endocrinology consult was obtained, and clinical evaluation revealed a clinically asymptomatic and euthyroid patient, with no family history of thyroid disease or supplement use, and there was no goiter. Assay interference was excluded by analyzing her thyroid function tests on a different platform, which yielded similar biochemical results. Subsequently, a polyethylene glycol (PEG) precipitation test was performed. Her pre-PEG TSH of 29.24 mIU/L decreased significantly to 2.78 mIU/L post-PEG. This yielded a remarkably low TSH recovery rate of 9.5%, strongly indicating the presence of macroTSH. Levothyroxine was then stopped, and she remained clinically euthyroid. Conclusion While gel filtration chromatography remains the gold standard for diagnosing this condition, PEG precipitation is a more accessible, cost-effective, and reliable screening method in clinical practice. A TSH recovery rate below 20% is considered highly suggestive of macro-TSH. Clinicians should maintain a high index of suspicion for macro-TSH in asymptomatic patients presenting with isolated TSH elevations that do not respond to thyroxine therapy. Prompt recognition prevents misdiagnosis and avoids the potential risks of unnecessary thyroid hormone replacement.
Hypothyroidism ; Thyrotropin

Introduction: Glycolysis continues after blood collection and may reduce glucose concentrations in vitro, potentially compromising diagnostic accuracy. The effectiveness of glycolysisinhibiting additives differs among blood collection tubes. Citrate rapidly inhibits glycolysis through immediate acidification, whereas fluoride acts more slowly by inhibiting enolase at a later stage of the glycolytic pathway. This study aimed to compare short-term glucose stability in four commonly used blood collection tubes under routine laboratory conditions. Methodology: Venous blood samples were collected from 100 volunteers into Rapid Serum Tubes (RST), Barricor tubes, Fluoride tubes, and Citrate tubes. Glucose concentrations were measured at 30 and 60 minutes after collection using the hexokinase method. A repeated-measures ANOVA was performed to evaluate the effects of Time, Tube Type, and the Time × Tube interaction (α = 0.05), followed by Bonferroni-adjusted pairwise comparisons. Results: At 30 minutes, glucose concentrations were highest in the Fluoride tube (5.528 mmol/L), followed closely by the Citrate tube (5.505 mmol/L), while lower values were observed in RST (5.434 mmol/L) and Barricor tubes (5.430 mmol/L). By 60 minutes, glucose levels had declined in all tubes; however, the decrease was more pronounced in serum-based tubes. RST values fell to 5.277 mmol/L and Barricor to 5.300 mmol/L, whereas Fluoride and Citrate tubes remained relatively stable at 5.449 mmol/L and 5.489 mmol/L, respectively. Overall, glucose decreased significantly between 30 and 60 minutes (mean decrease = 0.096 mmol/L, p <0.001; partial η² = 0.705). Tube Type also had a significant effect on glucose concentrations (F(3,297) = 42.06, p <0.001; partial η² = 0.298). Conclusion Fluoride and Citrate tubes provided the most effective preservation of glucose concentrations over 60 minutes, showing minimal glycolytic decline. In contrast, RST and Barricor tubes demonstrated significantly greater glucose loss, highlighting the importance of rapid processing when serum-based tubes are used.
Glucose

Introduction: Prolactin (PRL) exists in different forms in human serum. The predominant form is monomeric PRL (molecular mass 23 kDa) with smaller amounts of big PRL (molecular mass 50–60 kDa) and at times macroprolactin (molecular mass 150–170 kDa). Macroprolactin, generally considered to be biologically inactive, accounts for the major part of prolactin in some patients. Different immunoassays for prolactin differ in reactivity with this macromolecular complex. Aim: The present study was undertaken to assess the incidence of macroprolactinaemia in our cohort of hyperprolactinemic patients. Method: 204 samples with hyperprolactinemia were evaluated for macroprolactinemia by polyethylene glycol (PEG) precipitation and gel fi ltration chromatography (GFC). Recoveries <60% after PEG precipitation were considered to have macroprolactinaemia. Results: A total of 43 (21%) of these patients had less than 60% recovery after PEG precipitation. GFC confi rmed that in seven of these patients macroprolactin was the major part of the prolactin. Recoveries were < 40% PEG precipitation in these samples. Combined macro and hyperprolactinemia was observed in two samples and the recovery after PEG precipitation was >40% but 50%. The incidence of macroprolactinemia in our cohort of hyperprolactinaemic patients was noted to be 4.4%. Conclusion: Macroprolactin is a signifi cant cause of misdiagnosis, unnecessary investigation, and inappropriate treatment and hence it is useful to screen all patients with high PRL levels with PEG precipitation and to apply GFC to samples with recoveries <50%.