Harold P. Schedl

Bio: Harold P. Schedl is an academic researcher. The author has contributed to research in topics: Excretion & Creatine. The author has an hindex of 1, co-authored 1 publications receiving 169 citations.

Creatinine excretion: variability and relationships to diet and body size.

Abstract: In general, rates of addition of creatine to and loss of creatinine from the precursor pool depend upon the dietary intake and synthesis of creatine and the conversions of phosphoryl creatine and creatine to creatinine. Meat in a usual diet can appreciably expand the pool because of the slow turnovers of the precursors. Thus, 24 hour urinary creatinine contains a component from that day's turnover of stored creatine ingested previously. During this study, ingestion of creatine and creatinine free, but adequate protein diets, adjusted pool size toward supply and demand and lowered creatinine excretion as much as 30 per cent. For any population, correlation coefficients between estimates of body size or metabolically effective tissue and urinary creatinine depend in part on the expansion of the precursor pool. By serial daily creatinine analyses over long experimental periods on a metabolic ward, "timing" artifact in 24 hour collections was minimized; this is an important source of error if single 24 hour or random samples are used.

Serum creatinine as an index of renal function: new insights into old concepts.

Abstract: The serum creatinine concentration is widely interpreted as a measure of the glomerular filtration rate (GFR) and is used as an index of renal function in clinical practice. Glomerular filtration of creatinine, however, is only one of the variables that determines its concentration in serum. Alterations in renal handling and metabolism of creatinine and methodological interferences in its measurement may have a profound impact on the serum concentration of creatinine. We review the fundamental principles of physiology, metabolism, and analytical chemistry that are necessary to correctly interpret the serum creatinine concentration. These principles are then applied to important clinical circumstances, including aging, pregnancy, diabetes mellitus, drug administration, and acute and chronic renal failure. Despite numerous limitations, serum creatinine remains a useful clinical tool, but more accurate measures of renal function are frequently necessary.

Methods for the assessment of human body composition: traditional and new.

Abstract: Renewed interest in the assessment of human body composition has stimulated the need for a balanced understanding of available methodologies of estimating fat-free mass and percent body fat. This review summarizes the physical bases and assumptions, describes applications, and discusses the theoretical and practical limitations of currently available indirect methods. Although standard methods are discussed, recent modifications and adaptations are emphasized.

Measurement of muscle mass in humans: validity of the 24-hour urinary creatinine method.

Abstract: Measuring muscle mass is an important component of the nutritional assessment examination and a suggested index of this body space is the 24-h urinary excretion of creatinine. The method originated from studies in a variety of animal species in whom early workers found a parallelism between total body creatine and urinary excretion of creatinine. Assuming that nearly all creatine was within muscle tissue, that muscle creatine content remained constant and that creatinine was excreted at a uniform rate, an obvious "corollary" was that urinary creatinine was proportional to muscle mass. The so-called "creatinine equivalence" (kg muscle mass/g urinary creatinine) ranged experimentally from 17 to 22. One of the limiting factors in firmly establishing this constant and its associated variability was (and is) the lack of another totally acceptable noninvasive technique of measuring muscle mass to which the creatinine method could (or would) be compared. An improved understanding of creatine metabolism and a variety of clinical studies in recent years has tended to support the general validity of this approach. However, specific conditions have also been established in which the method becomes either inaccurate or invalid. While creatinine excretion may serve as a useful approximation of muscle mass in carefully selected subjects, there remains a need for accurate and practical indices of muscle mass for use in the individuals in whom the method cannot be reliably applied.

Measurement of renal function in chronic renal disease

Abstract: Patient 1. A 42-year-old woman first was evaluated at the New England Medical Center after an episode of dysuria that resolved following treatment with an antibiotic. Her weight was 55.5 kg and the blood pressure was 150/100 mm Hg. Urinalysis disclosed 3+ protein, 5—15 red blood cells/high-power field, occasional granular casts, and oval fat bodies. A 24-hour urine sample contained 3.9 g protein and 820 mg creatinine. Serum creatinine was I. I mg/dl and creatinine clearance was 52 mI/mm. Because of the laboratory abnormalities, a mild sensorineural hearing loss bilaterally, and a family history of renal disease, a diagnosis of hereditary nephritis was made. Hypertension was treated with hydrochlorothiazide, During the next 3 years, her blood pressure was usually in the range of 130/95 mm Hg, but occasional values were as high as 180/110 mm Hg. Urinary protein excretion declined to 0.64 glday. She complained of nocturia but otherwise was asymptomatic. At age 45 years, her blood pressure was 160/85 mm Hg and serum creatinine was 2.2 mg/dI. Propranolol, 20 mg twice daily, was added to her regimen, and a 40 g protein diet was prescribed. During the next 4 years, her hypertension was treated with hydrochlorothiazide, 50 mg/day; atenolol, 50 mg/day; and captopril, 25 mg/day; her blood pressure was usually in the range of 130—140/80—90 mm Hg. Body weight and serum albumin concentration remained stable. Serum creatinine ranged from 2.2 to 2.5 mg/dl. At age 49 years, she entered the feasibility phase of the Modification of Diet in Renal Disease (MDRD) Study. She was randomly assigned to follow a very low protein diet (16 g/day, equivalent to 0.28 g of protein/kg ideal body weight/day) supplemented with 12 g/day of an

Serum creatinine levels in the US population: Third National Health and Nutrition Examination Survey

Abstract: This report describes the distribution of serum creatinine levels by sex, age, and ethnic group in a representative sample of the US population. Serum creatinine level was evaluated in the third National Health and Nutrition Examination Survey (NHANES III) in 18,723 participants aged 12 years and older who were examined between 1988 and 1994. Differences in mean serum creatinine levels were compared for subgroups defined by sex, age, and ethnicity (non-Hispanic white, non-Hispanic black, and Mexican-American). The mean serum creatinine value was 0.96 mg/dL for women in the United States and 1.16 mg/dL for men. Overall mean creatinine levels were highest in non-Hispanic blacks (women, 1.01 mg/dL; men, 1.25 mg/dL), lower in non-Hispanic whites (women, 0.97 mg/dL; men, 1.16 mg/dL), and lowest in Mexican-Americans (women, 0.86 mg/dL; men, 1.07 mg/dL). Mean serum creatinine levels increased with age among both men and women in all three ethnic groups, with total US mean levels ranging from 0.88 to 1.10 mg/dL in women and 1.00 to 1.29 mg/dL in men. The highest mean creatinine level was seen in non-Hispanic black men aged 60+ years. In the total US population, creatinine levels of 1.5 mg/dL or greater were seen in 9.74% of men and 1.78% of women. Overall, among the US noninstitutionalized population, 10.9 million people are estimated to have creatinine values of 1.5 mg/dL or greater, 3.0 million have values of 1.7 mg/dL or greater, and 0.8 million have serum creatinine levels of 2.0 mg/dL or greater. Mean serum creatinine values are higher in men, non-Hispanic blacks, and older persons and are lower in Mexican-Americans. In the absence of information on glomerular filtration rate (GFR) or lean body mass, it is not clear to what extent the variability by sex, ethnicity, and age reflects normal physiological differences rather than the presence of kidney disease. Until this information is known, the use of a single cutpoint to define elevated serum creatinine values may be misleading.