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Technical Briefs |
1
Office of the Chief Medical Examiner, Campus Box 7580, Chapel Hill, NC 27599-7580;
2
Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, Gainesville, FL 32610-0275;
3
Department of Pharmacy Practice, University of Florida College of Pharmacy, Gainesville, FL 32610-0486;
a address
correspondence to this author at: Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, P.O. Box 100275, Gainesville, FL 32610-0275, fax 352-846-1586, e-mail bruce-goldberger{at}ufl.edu
Forensic urine drug-testing laboratories routinely evaluate the suitability of urine specimens to assess potential adulteration, substitution, or dilution. For example, the measurement of urinary creatinine and specific gravity is performed by these laboratories to determine whether a specimen is abnormally dilute (1).
Creatine is synthesized endogenously and is stored in skeletal muscle in a high-energy phosphorylated form. During muscle contraction, creatine and creatine phosphate are spontaneously converted to creatinine. Creatinine is eliminated from the body by renal excretion at a relatively constant rate, making it a clinically chosen measurement to indicate renal function and a forensically chosen measurement to detect dilute urine and potentially adulterated specimens (2).
Creatine has been available since the early 1960s as a dietary supplement purported to ergogenically enhance short-term, high-intensity exercise (3)(4). However, it was not until the 1990s, when oral creatine supplements became widely available over the counter, that creatine became a popular performance and strength enhancer among amateur and professional athletes.
Creatine and creatinine can be obtained exogenously through dietary intake of meat or ingestion of dietary supplements. Creatine supplements are an alternative to a large dietary intake of meat because a daily recommended maintenance dose of 5 g of creatine is equivalent to ~1 kg (2.2 pounds) of uncooked meat (5). Studies suggest that dietary contribution of creatine and creatinine may influence urinary excretion patterns of creatinine (2)(6).
Given these reported effects of exogenous ingestion of creatine, an investigation into the potential effects of oral creatine supplementation on urinary measurements of creatinine was undertaken to determine whether laboratories should reevaluate their methods of performing specimen integrity checks. In addition, urinary pH, specific gravity, and creatinine clearance were monitored during the course of the study.
The duration of the study was 14 days: 2 days before and after completion of creatine supplementation, and 10 days of supplementation. Four volunteer subjects (ages, 24–49 years), two males and two females, participated in the study. All subjects were normally active, healthy, drug-free adults of average weight (56–100 kg) with normal renal function. Subjects continued their usual lifestyles, and restraints on general daily activities or dietary intake, including consumption of fluids, were not imposed.
Oral creatine supplementation followed the manufacturer’s recommended dose of ~5 g of creatine monohydrate dissolved in 237 mL (8 fluid ounces) of Gatorade® (5). The initial loading phase consisted of a dose administered four times daily for 5 days. The subsequent maintenance phase included one dose daily for 5 days.
An aliquot of urine was collected during all voids. In addition, 24-h pooled urine specimens and serum specimens were obtained on days 2, 7, and 12. All specimens were stored frozen at -20 °C in polystyrene tubes. Urine integrity tests, including creatinine, pH, and specific gravity, were performed using routine clinical laboratory methodologies. The pH was measured with pH indicator paper (Whatman International), and the specific gravity was measured using an Atago urine specific gravity refractometer. The urine and serum creatinine values were measured by the modified Jaffé reaction, using Boehringer Mannheim Diagnostics reagents on a Hitachi 717 automated chemistry analyzer.
A total of 307 discrete urine specimens were obtained during the course
of the study. The data are presented in Table 1
, and individual subject plots of all discrete urine
specimen values are shown in Fig. 1
. All creatinine clearance values were within the appropriate
reference intervals.
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Our data were compared with criteria for dilute specimens established by the College of American Pathologists and the Substance Abuse and Mental Health Services Administration. These criteria state that a urine specimen with a specific gravity <1.003 and a creatinine concentration <200 mg/L is dilute (1)(7). In addition, specimen pH was compared with the normal urinary pH range of 4.5–8.0 (2).
The majority of discrete creatinine and specific gravity values and all discrete pH values were within established limits with no obvious trends. Furthermore, regression analysis of the intrasubject specific gravity and creatinine values revealed correlation coefficients of 0.606–0.827, indicating that these measurements were correlated (8).
This short-term study investigated the effects of oral creatine supplementation on urinary creatinine, pH, and specific gravity values. Individual plots of all discrete urine specimen values did not reveal any apparent effect of creatine administration on these measurements. In conclusion, these data suggest that oral creatine supplementation administered at recommended daily doses does not influence routinely used urine integrity tests.
References
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