OCTOBER D87 - Voice For The Defense Online

Conversion RatiosUpon ingestion into the body, alcohol issecreted into the bladder nrine by diffusionthrough the kidneys. Many scientific studieshave consistently shown that the concentrationof alcohol in the urine at the timeit is secreted in the kidneys is approximately1.33 times that in the blood.g Thepercentage of alcohol in a specimen ofurine as it is secreted in the kidney, if dividedby 1.33, is said to provide a reasonablynccrrrnfe esthate of the alcoholconcentration of the blood.However, 1.33 represents the averagealcohol ratio between the concentration ofalcohol in the blood and in the urine.'O Indeed,according to the American MedicalAssociation, the figures for the urine-bloodalcohol ratio range from 1.12 to 1.51 .'IIn a recent study of approximately 5,000forensic cases with a positive alcohol result,over 1,000 were available in whichboth blood and urine were present for comparisonof alcohol content. The overallurine to blood alcohol concentration ratiowas 1.57:1.00 with a range of 0.7:l.O upto 21.0: 1.00.'2 This extremely wide rangeof values demonstrates that a large degreeof error would probably be introduced ifa mean ratio (1.33) was used when predictingblood alcohol level from a urinealcohollevel.13Indeed, this is the position held by a majorityof the scientific con~munity.~~ It isthe majority opinion of the scientificcommunity that urine-blood conversion isnot a means by which to reliably and accuratelydetermine blood alcohol concentrationand intoxication15. In this regard,the Department of Transportation hastaken the position of discouraging urinalysisbecause of "various problems in theinterpretation of the results of analysis ofurine for alcohol which cannot be readilyovercome in law enforcement practice.'"6Abso~lion of AlcoholEthyl alcohol, or ethanol, is the alcoholcommonly found in most libations. Afteringestion, it then passes to the stomachwhere it is absorbed into the small intestine."Because of an enzyme calledalcohol dehydragenase (ADH), the vastmajority of the ethanol is metabolized bythe liver. In fact, only 3% of alcohol ingestedis excreted through the urine.18Otherwise, the blood eventually absorbsalcohol and it is passed to the brain andother organs. Urine is then formed in thekidneys by filtration and separation ofblood cells from plasma by simple diffusion.The particles that are fdtered out withwater form a liquid glomerula filtrate, orurine.19 This liquid then undergoes reahsorptionso tbat useful by-products andwater are retained by the body and hazardoussubstances are expelled. Thereafter,the filtrate (urine) passes from the kidneysto the ureter and is stored in the bladder.20Although the percentage of alcohol in aspecimen of urine as it is secreted in thekidney will provide a reasonable estirnateof the alcohol content in the blood, urinefrom the kidneys is not easily obtainable.Urine from the bladder is easily obtainable,but relating it to freshly secretedurine in the kidney is difficult."The bladder is evacuated at relatively infrequentintervals. Thus, the pool of urinefound in the bladder at any given time representsthe accumulation of secreted urinefrom the kidney as of the last emptying ofthe bladder. However, it must be rememberedthat a specimen of bladder urine onlyindicates the urine alcohol content at thetime the specimen was obtained. In thisregard, estimationof theBAC (i.e., degreeof intoxication) at a time prior to the procurementof the specimen can be extrapolated(the time of driving), provided thespecimen was taken during the time thepeak blood alcohol percentage had beenreached.However, this would only be possible ifthe test subject's absorption and eliminationrates were known at the time the specimenwas taken.22 With regard to properevaluation of a subject's absorption andelimination rates for law enforcement testing,it can be said that such rates are notknown and are continuously guessed at orreplaced by the use of average rates bystate expert witnesses.Extrapolation and Correlation ofUrine Alcohol Concentration(UAC) to Blood AlcoholConcentralion (BA C)Naturally, upon ingestion of alcohol, theblood will absorb most of it prior to thealcohol reaching the kidney and eventuallythe bladder. This is referred to as "preabsorptionphase."13 It is during this initialphase that alcohol in the blood will beof a higher concentration than in the bladderAs pointed out by researchers N. Dunnettand K. J. Kimber, the BAC reachesits peak level prior to bladder urinereaching its peak. The ratio of BAC toUAC during the pre-absorption phase isgreater than 1:1.25 If one were to sampleurine and blood simultaneously during thefirst hours after alcohol consumption, theUAC would be much lower than the BAC.Dunnett and Kimber plotted a bellshapedcurve to demonstrate the absorptionof alcohol by the body. The downwardportion of the curve represents the "eliminationphase" or "post-absorption" areawhere the BAC to UAC ratio is less than1:l and remains relatively constant. Thisis where the sampling of bladder urineshould occur.26 To determine if a subjectis in the "elimination phase," one mustwithdraw at least two samples at spaced intervals.If the second sample's UAC readingis higher than the first, the "elitninationphase" has been entered.27 However,during this phase, pooled urine may representan inflated reading as a result of urineretention.28 Richard E. Erwin's hypothetedemonstrates the possibility of skewedresults:Assume for instance that an alcoholfreesubject consunled a largeamount of alcohol. That at the endof one hour the individual's bloodalcohol concentration was .lo%. Ifall of the urine was collected andpooled within that hour's time itwould represent concentrations rangingfrom 0.0% to concentrations ashigh as 0.13%, that urine accnmnlatedat the very end of the drinkingprocess. The concentration, however,of the pooled urine specimenswould be an average of the twolevels or about 0.07%.On the other hand if you were toassume tbat a subject had been drinkingfor some time and had obtaineda blood alcohol level of 0.15% andthat he emptied his bladderjust priorOctober 1987 1 VOICE for the Deferrse 27