Quantification of insulin in dried blood spots.

A method has been developed in which the concentrations of insulin in dried blood spots on filter paper can be estimated. The technique involves elution of blood from the paper, evaporation, and rehydration in assay buffer. The resuspended samples are then assayed by radioimmunoassay. The ratio of control plasma to control dried blood spot insulin values is used as a conversion factor for unknown samples on paper to express the dried blood spot insulin concentration in plasma equivalents. Intra-assay variability was 14%, and interassay variability was 25%, but the elution conversion factor had a variability of about 40% among individuals. This technique has substantial advantages for field studies, but elevated values should be confirmed by a venous plasma sample measurement in a conventional radioimmunoassay.

Acanthosis nigricans.

Acanthosis nigricans is a lesion affecting localized areas of the skin in persons with obesity and/or hyperinsulinemia. Roughening of the skin correlates with histological papilomatosis and the apparent darkening is due to hyperkeratosis. Biochemical mechanisms for developing this hyperplastic lesion are unclear, but likely involve local cutaneous growth factors. Cross sectional surveys of unselected populations have demonstrated that young children have low prevalences of obesity and acanthosis nigricans, but the prevalences of both increase with increasing age until plateaus are reached after the age of ten. Nearly 40% of Native American teenagers have acanthosis nigricans, whereas about 13% of African American, 6% of Hispanic, and less than 1% of white, non-Hispanic children aged 10-19 have clinically apparent acanthosis nigricans. We conclude that the presence of this skin lesion is a clinical surrogate of laboratory-documented hyperinsulinemia. Acanthosis nigricans identifies a subgroup within an ethnic group who have the highest insulin concentration, the most severe insulin resistance, and thus the highest risk for the development of type 2 diabetes.

Acanthosis Nigricans among Native Americans: an indicator of high diabetes risk.

Prevalence of the skin lesion acanthosis nigricans was determined in two tribal communities in Texas and Nebraska. Thirty-eight percent of the Alabama-Coushatta tribe of Texas had acanthosis nigricans. Nineteen percent of Omaha and Winnebago tribal children had the skin lesion; the youngest children had the least acanthosis nigricans. Among weight-matched Alabama-Coushatta, fasting insulin concentrations were twofold higher in subjects with the lesion. It was concluded that acanthosis nigricans is highly prevalent among Native Americans and that its presence suggests insulin resistance. Thus, it may identify those with the highest risk for non-insulin-dependent diabetes mellitus in this population.

Diurnal variation of serum calcium and phosphorus in postmenopausal women.

Serum calcium, ionized calcium, and phosphorus have been obtained at hourly intervals in nine healthy postmenopausal women. The hourly means of ionized calcium and phosphorus demonstrate significant diurnal variation with a similar apogee, nadir, and periodicity (24 hours). These results are distinct from the diurnal variation of ionized calcium and phosphorus previously reported for young men and provide more evidence of an altered mineral hemostasis in postmenopausal women.

Cystinosis presenting with features suggesting Bartter syndrome. Case report and literature review.

Features suggestive of Bartter syndrome (hypokalemia, hypochloremic metabolic alkalosis, and normal blood pressure despite hyperreninemia and hyperaldosteronism) were found in a 5-year-old black child with cystinosis and Fanconi syndrome. Review of his medical records revealed that these abnormalities had probably been present when he first became clinically ill at 2 years of age. Sodium and potassium chloride supplementation lead to improved growth and strength, partial correction of his electrolyte abnormalities, and a decrease in markedly elevated plasma renin activity. Literature review disclosed a similar presentation in four Caucasian children with cystinosis. Biochemical findings compatible with Bartter syndrome can occur together with evidence of generalized proximal renal tubular dysfunction (Fanconi syndrome) in nephropathic cystinosis.