Older Adult Labs Medsurg

220 MEDSURG Nursing—August 2005—Vol. 14/No. 4

Interpreting Laboratory ValuesIn Older Adults

Nancy Edwards, PhD, RN,C, is anAssociate Professor, Purdue UniversitySchool of Nursing, West Lafayette, IN.

Carol Baird, DNS, APRN, BC, is anAssociate Professor, Purdue UniversitySchool of Nursing, West Lafayette, IN.

Nancy EdwardsCarol Baird

may include gender, body mass,alcohol intake, diet, and stress(Fischbach, 2004). Technical fac-tors such as collection site, col-lection time, tourniquet applica-tion, and specimen transportationalso can affect results but usuallycan be controlled by followingstandardized laboratory proce-dures (Brigden & Heathcote,2000).

Results of diagnostic testingin older adults may have differentmeanings from the results foundin younger individuals. Nursesshould recognize that no generaltrend exists for the direction ofchange in laboratory values forolder adults. For some tests, olderadults have higher than normalvalues and for others, lower val-ues; some remain unchanged.Changes in laboratory values canbe classified in three generalgroups: (a) those that change withaging; (b) those that do notchange with aging; and (c) thosefor which it is unclear whetheraging, disease, or both influencethe values (Tripp, 2000). Commonlaboratory tests with interpreta-tions for older adults are present-ed.

Interpreting ReferenceRanges

The accepted, normal rangesof values typically reported maynot be applicable for older adults.

Results of common labora-tory tests must be interpretedwith care in older adults.Laboratory results that varywith age are presented, alongwith possible causes and inter-pretations of results.

John Doe, 83 years old, comes tothe clinic complaining of in-

creasing fatigue and weakness. Hispast medical history includes dia-betes mellitus, chronic anemia,and hypertension. The 5’10” man isthin (148 pounds) with small mus-cle mass. His skin color is palepink. A battery of diagnostic testsreveals the following: hemoglobin11.2 g/dL, hematocrit 40%, whiteblood cells 5,000/ml, fasting bloodsugar 183 mg/dL, blood urea nitro-gen 30 mg/dL, serum creatinine 1.9mg/dL, and serum albumin 2.3g/dL. The nurse is uncertain whichlaboratory values are significant inconsidering Mr. Doe’s care plan.

This case illustrates the diffi-culty in interpreting laboratoryvalues for older adults, which is acomplex task with varied opinionsabout what is normal. Multipleconfounding factors make inter-pretation and use of laboratoryresults in older patients challeng-ing. Some of the factors include(a) physiologic changes associat-ed with aging, (b) the high preva-lence of chronic conditions, (c)changes in nutrition and fluid con-sumption, (d) lifestyle changes,and (e) pharmacologic regimes(Brigden & Heathcote, 2000).Laboratory test results also maybe affected by many factors otherthan aging. Influencing factors

MEDSURG NURSINGCE Objectives and Evaluation Form appear on page 230.

MEDSURG Nursing—August 2005—Vol. 14/No. 4 221

Interpreting Laboratory Values in Older Adults

Reference ranges may be moreappropriate. Normal ranges areobtained by determining themean of a random sample ofhealthy individuals, usually ages20 to 40 years, in order to identifytwo standard deviations on eitherside of the mean. The concept ofnormal range, however, is notuseful in determining age-relatednorms for older adults (Luggen,2004).

Reference ranges or referencevalues are preferred concepts.Reference ranges or referencevalues are those intervals withinwhich 95% of the values fall for aspecific population (Lab TestsOnline, 2001). For example, geri-atric reference ranges are thoseintervals within which 95% of val-ues for persons over 70 years ofage would fall. It must be cau-tioned, however, that someresearchers recommend notusing reference ranges for labora-tory test parameters pertainingto older adults because it is diffi-cult to differentiate whetherresults are a sign of a disease orare related to normal aging(Luggen, 2004). However, refer-ence ranges are useful in somesituations. The use of referenceranges allows for recognition ofthe special needs of the popula-tion in question. Referenceranges are calculated not just forolder adults, but also forneonates (especially low-birth-rate infants), adolescents, andpregnant women. In addition, spe-cific reference ranges are knownfor tests for other special popula-tions (for example, serum ery-thropoietin in adult athletes suchas marathon runners).

Laboratory values falling out-side the normal ranges may indi-cate benign or pathologic condi-tions in the older adult(Fischbach, 2004). Values withinthe expected normal referenceranges, however, may also indi-cate new or progressing patho-

logic conditions in certain olderadults. Nurses working with olderadults should consider the totalassessment rather than simplyrelying on laboratory diagnostictesting. For example, goals ofmanagement of diabetes shouldbe individualized. The principalgoal would be to enhance qualityof life without undue risk of hypo-glycemia. It usually is best toachieve fasting blood glucose lev-els of less than 140 mg/dl.However, in the frail elderly, it isbest to avoid fasting or bedtimeplasma glucose levels of less than100 mg/dl if the patient is oninsulin or sulfonylurea treatment(Reed & Mooradian, 1998).

Serum creatinine is a secondexample of a laboratory test inwhich results may be within thespecified reference range and yetindicate pathology for the olderadult. Creatinine is a product ofcreatine phosphate, used inskeletal muscle contraction.Endogenous creatinine produc-tion is constant as long as musclemass remains constant (Pagana &Pagana, 2002). The mechanismsthat regulate the older individ-ual’s serum creatinine levels with-in the accepted reference rangetend to overestimate renal func-tioning as a measure of glomeru-lar filtration rate. Serum creati-nine and blood urea nitrogen(BUN) levels in the high-normalcategory may represent signifi-cant renal dysfunction in theolder adult who has inadequateprotein intake (Daniels, 2002).

Specific Laboratory TestsHemoglobin (HGB). While the

results of studies of the effects ofaging on the hematologic systemvary (Brigden & Heathcote, 2000;Nilsson-Ehle, Jagenburg, Landahl,& Swanborg, 2000), research doesindicate that older individualsmay have changes in hemoglobinand erythrocyte synthesis causedby changes in iron and vitamin B12

absorption (Giddens, 2004). Im-paired erythrocyte production,blood loss, increased erythrocytedestruction, or a combination ofconditions have also been identi-fied as causes for lowered hemo-globin (Giddens, 2004). Kee(2002) defines hemoglobin asabnormal if less than 13.5 gm/dlfor males and 12.0 gm/dl forfemales. Recent studies witholder adults, however, suggestlower levels may be acceptable.The currently reported lowestacceptable value for older adultsis 11.5 gm/dl for males and 11.0gm/dl for females (Brigden &Heathcote, 2000) (see Table 1).

Hemoglobin may be lower inolder adults due either to normalaging changes or illnesses suchas anemia. Manson and McCance(2004) identify impaired erythro-cyte production, blood loss,increased erythrocyte destruc-tion, or a combination of condi-tions as causes for anemia. Mostinstances of anemia are associat-ed with chronic conditions suchas renal insufficiency or gastricbleeding (Giddens, 2004). Anemiamay be a serious conditionbecause it places the older indi-vidual at greater risk for circula-tory and oxygenation problems(Tripp, 2000). A reduction ofhemoglobin can result in adecrease in oxygen content andan increase in fatigue. Signs ofanemia may not be noticed if theanemia is mild, but some individ-uals may present with shortnessof breath, fatigue, and paresthe-sia (Manson & McCance, 2004). Acombination of vague symptomsand an unclear clinical picturemay lead the health care providerto attribute the symptoms to “oldage” and not to a treatable condi-tion.

Hematocrit (HCT). Changes inhematocrit may reflect fluidand/or nutritional status in theolder adult (Fischbach, 2004;Giddens, 2004). An increase in the



hematocrit may signal volumedepletion, while a decrease maybe a result of conditions accom-panied by fluid overload ordietary deficiencies. Hematocrit,the percentage of total blood vol-ume that represents erythro-cytes, may be normal if values are30% to 45% for older males and36% to 65% for older females(Desai & Isa-Pratt, 2002) (seeTable 1).

White blood cells (WBC).Whether total leukocyte count isaffected by aging is controversial.However, there are definitechanges in that the T cells areless responsive to infection(Fulop et al., 2001; Sester et al.,2002). Immunity gradually de-clines after age 30 to 40 years

(Rybka et al., 2003) (see Table 1).A decreased WBC value mayresult from specific disease(myeloma, collagen vascular dis-orders), infection or sepsis(pneumonia, urinary tract infec-tions), or medications (cytotoxicagents, analgesics, phenoth-iazides), and should not be attrib-uted to advancing age (Fischbach,2004). This lowered WBC count ina healthy individual may result inan absence of elevated whiteblood cells in the presence ofsevere infection. Medicationssuch as steroids also may influ-ence the immune response(Giddens, 2004). Because of theslower immune response, com-mon symptoms of infections,such as enlarged lymph glands,

fever, or pain, may be decreasedin severity or absent in the olderadult (Beers & Berkow, 2000).Nurses should be vigilant inefforts to detect other signs ofinfections in the older adult, suchas confusion. Because of the con-cern for serious undetected infec-tion, nurses should educate olderadults about infection preventiontechniques, such as hand wash-ing and timely vaccination forinfluenza and pneumonia.

Platelets (Plt). Aging usuallycauses a decline in bone marrowfunction, which may contributeto lowered platelet counts anddecreased platelet function(Luggen, 2004). Studies also sug-gest that platelet adhesivenessincreases with age, with no

Table 1.Geriatric Laboratory Values and Interpretations of Hematology

Test

Hemoglobin

Hematocrit

White Blood Cells

Platelets

Normal Adult ValueMale (M)

Female (F)

M 13.0 gm/dlF 12.0 gm/dl

M 40% - 54%F 36% - 46%

4,500 - 10,000 µl/mm3

150,000 - 400,000 µl

Geriatric Value

M 11.5 gm/dlF 11.0 gm/dl

M 30% - 45%F 36% - 65%

3,000 - 9,000 µl/mm3

Minimal change

Implications

↓: Anemias, cirrhosis of liver, leukemias,Hodgkin’s disease, cancer (intestine, rec-tum, liver, or bone), kidney disease↑: Dehydration, COPD, CHF, polycythemia

↓: Anemias, leukemia, Hodgkin’s disease,multiple myeloma, cirrhosis of liver, pro-tein malnutrition, peptic ulcer, chronicrenal failure, rheumatoid arthritis↑: Dehydration, severe diarrhea, poly-cythemia vera, diabetic acidosis, emphyse-ma, transient cerebral ischemia

↓: Hemotopoietic diseases, viral infections,alcoholism, systemic lupus erythematous(SLE), rheumatoid arthritis↑: Acute infection, tissue necrosis,leukemias, hemolytic anemia, parasitic dis-eases, stress

↓: Idiopathic thrombocytopenia purpura,multiple myeloma, cancer, leukemias, ane-mias, liver disease, SLE, kidney disease↑: Polycythemia, trauma, post-splenecto-my, metastatic carcinoma, pulmonaryembolism, tuberculosis

Source: Brigden & Heathcote, 2000



changes in numbers (Thibodeau& Patton, 2004). The ability of theolder adult’s body to respond tomajor blood loss by regeneratingplatelets may be inadequate,leading to inadequate clotting(Beers & Berkow, 2000) (seeTable 1). The patient also must beassessed for potential or hiddenblood losses, such as occultblood in stools and emesis.

Erythrocyte sedimentation rate(ESR). Brigden (1999) noted thatthe erythrocyte sedimentationrate increases with age, but thecause of this increase isunknown. ESR measures the rateat which red blood cells (RBCs)settle in 1 hour. An annual rate ofincrease in time of sedimentationrate for older adults has been

quantified at 0.22 mm/hour/yearfrom age 20 years (Duthie &Abbasi, 1991). An elevated ESRmay indicate the presence ofinflammation. Inflammation caus-es an alteration in blood proteins,making the RBCs heavier andcausing them to settle faster(Fischbach, 2004). The accept-able reference range for the olderadult is 40 mm/hour for malesand 45 mm/hour for females(Brigden & Heathcote, 2000) (seeTable 2). Because a slight eleva-tion may or may not reflect thepresence of an underlying inflam-mation, confirmation of a clinicalproblem may be difficult. Nursesshould rely on other assessmentfactors, such as visible inflamma-tion, pain, or fever, to determine a

possible clinical condition. Serum iron. Serum iron is

decreased in many older adults,resulting in iron deficiency ane-mia as the most common form ofanemia seen in older adults(Tripp, 2000) (see Table 2). Onepossible explanation is an age-related decrease in hydrochloricacid (HCl) in the stomach (Beers& Berkow, 2000). HCI is importantfor facilitating iron absorption inthe intestines. Serum iron, totaliron-binding capacity, and ironstores decrease with age(Daniels, 2002). When there is adecrease in iron stores, serum-ferritin increases and serumtransferrin decreases. The de-crease in transferrin levels mayindicate a decrease in liver syn-

Table 2.Geriatric Laboratory Values and Interpretations of Erythrocyte Sedimentation Rate,

Iron Metabolism, and Vitamin B12

Test

ErythrocyteSedimentationRate (ESR)

Serum Iron

Ferritin

Vitamin B12


Female (F)

M 0 - 15 mm/hrF 0 - 20 mm/hr

50-150 µg/dl

M 15 - 445 ng/mlF 10 - 235 ng/ml

200 - 900 pg/ml

Geriatric Value

M 0 - 40 mm/hrF 0 - 45 mm/hr

60 - 80 µg/dl

10 - 310 ng/dl

150 pg/ml

Implications

↓: Polycythemia, CHF, degenerative arthri-tis, angina pectoris↑: Rheumatoid arthritis, rheumatic fever,acute MI, cancer (stomach, colon, breast,liver, kidney), Hodgkin’s disease, multiplemyeloma, bacterial endocarditis, gout,hepatitis, cirrhosis of liver, glomeru-lonephritis, SLE, theophylline use.

↓: Iron deficiency anemia, cancer (stom-ach, intestine, rectum, breast), bleedingpeptic ulcers, protein malnutrition↑: Hemolytic, pernicious, and folic acidanemias; liver damage; lead toxicity

↓: Iron deficiency, inflammatory bowel disease, gastric surgery↑: Metastatic carcinoma, leukemias, lymphomas, hepatic diseases, anemias,acute and chronic infection, inflammation,tissue damage

↓: Pernicious anemia, malabsorption syndrome, liver disease, hypothyroidism↑: Acute hepatitis

Source: Brigden, 1999; Brigden & Heathcote, 2000; Kee, 2000; Tripp, 2000



thesis (Lab Tests Online, 2004).Decreased iron storage and iron-deficiency anemia, however, com-monly are caused by inadequatedietary intake of iron or loss ofiron through chronic or acuteblood loss (Beers & Berkow,2000). Nursing assessment shouldinclude a dietary assessment forreduced intake of iron-containingfoods and assessment of occultbleeding from the gastrointestinaltract.

Vitamin B12. Brigden andHeathcote (2000) report thatserum vitamin B12 levels maydecrease slightly with age (seeTable 2). The deficiency in B12may be due to chronic atrophicgastritis, an immune dysfunctionthat occurs more often in olderadults, or from a deficiency ofHCl, both leading to insufficientintrinsic factor and insufficientabsorption of vitamin B12 (Beers &Berkow, 2000). The low end of thereference range for vitamin B12 is150 pg/mL in the older adult asopposed to 190 pg/mL in ayounger adult (Brigden &Heathcote, 2000) (see Table 2).Assessment for pernicious ane-mia, including checking for neu-ropathies, such as weakness, dif-ficulty walking, and numbness ortingling, should be consideredwhenever anemia is present.

Total protein and albumin.Some serum protein levels, suchas albumin and total protein,

decline in older adults (Beers &Berkow, 2000). Changes in proteinmay reflect decreased liver func-tioning or inadequate nutritionalintake (Beers & Berkow, 2000).While all serum proteins arereduced, albumin is the most sig-nificantly influenced by aging(Beers & Berkow, 2000). Albuminlevels decrease each decade overthe age of 60, with a markeddecrease over 90 years of age(Daniels, 2002). In addition tobeing an indicator of disease ormalnutrition, low serum albuminis the most common cause of alow serum calcium level in olderadults, because most serum calci-um is protein-bound (Beers &Berkow, 2000) (see Table 3).

Renal function. As mentionedpreviously, relying on commonlyaccepted laboratory values indetermining renal function in theolder adult is difficult. The age-related 30% to 45% decrease infunctioning renal tissue and theglomerular filtration rate (GFR)leads to a decline in the creati-nine clearance (Brigden &Heathcote, 2000). Commonlyoccurring reduction in lean bodymass, decreased dietary proteinintake, or decreased hepatic func-tion may lead to decreases in theend products of metabolism,BUN, and creatinine (Brigden &Heathcote, 2000). BUN and creati-nine levels overestimate renalfunctioning, as measured by GFR

or creatinine clearance, becauseof the changes in body composi-tion (Engelberg, McDowell, &Lovell, 2000; Luggen, 2004). Adecrease in the lean body mass,relatively common in olderadults, results in reduced proteindegradation and nitrogen byprod-ucts of metabolism (BUN). Thedecline in muscle mass alsoresults in less creatinine produc-tion; serum creatinine values thusremain within normal limitsdespite diminished renal clear-ance capacity (Brigden &Heathcote, 2000) (see Table 4).

When considering age-relatedchanges, most physicians andadvanced practice nurses ques-tion the adequacy of BUN and cre-atinine as indicators of renal func-tion (Kennedy-Malone, Fletcher, &Plank, 2004). Therefore, measure-ment of urinary creatinine clear-ance takes on special significancein the older adult. Serum creati-nine is affected by bothdecreased GFR and body mass,while urinary creatinine clear-ance is affected only by glomeru-lar filtration (Lewis et al., 2004).Determining renal function bycreatinine clearance examinationis especially useful when treatingthe older adult with medicationsbecause of the potential for thedevelopment of drug toxicity,even with usual doses (Daniels,2002). Because it may be difficult

Table 3.Geriatric Laboratory Values and Interpretations of Serum Proteins

Test

Total Protein

Albumin

Normal Adult Value

6.0 - 8.0 g/dl

3.0 - 5.0 g/dl52 - 68% of total protein

Geriatric Value

5.6 - 7.6 g/dl

Slight decrease

Implications

↓: Prolonged malnutrition, low-protein diet,cancer (GI tract), severe liver disease, chronicrenal failure↑: Dehydration, vomiting, multiple myeloma

↓: Severe malnutrition, liver failure, renaldisorders, prolonged immobilization↑: Dehydration, severe vomiting, diarrhea

Source: Beers & Berkow, 2000; Kee, 2002



Table 6.Geriatric Laboratory Values and Interpretations of Hepatic Enzymes

Test

Serum AlanineAminotransferase(ALT, SGPT)

Serum AspartateAminotransferase(AST, SGOT)

AlkalinePhosphatase

Gamma-Gluta-Myltransferase(GGT)


Female (F)

10 - 35 U/I

8 - 38 U/l

20 - 130 U/I

M 4 - 23 IU/IF 3 - 12 IU/I

Geriatric Value

17 - 30 U/I

18 - 30 U/I

30 - 140 U/I

9 - 55 U/I

Implications

↓: Exercise, salicylates↑: Viral hepatitis, liver necrosis, CHF, acutealcohol intoxication

↓: Diabetic ketoacidosis↑: Acute MI, hepatitis, liver necrosis, mus-culoskeletal disease and trauma, pancreati-tis, cancer (liver), angina pectoris, muscletrauma related to IM injections

↓: Hypothyroidism, malnutrition, perni-cious anemia↑: Cancer (liver, bone), hepatitis, leukemia,healing fractures, multiple myeloma,rheumatoid arthritis, ulcerative disease

↓: None↑: Cirrhosis of liver, necrosis of liver, alco-holism, hepatitis, cancer (liver, pancreas,prostate, breast, kidney, liver, lung), dia-betes mellitus, acute MI, CHF, pancreatitis,cholecystitis, nephritic syndrome

Source: Brigden & Heathcote, 2000; Kee, 2002

Table 4.Geriatric Laboratory Values and Interpretations of Selected Renal Function Tests

Test

BUN

Creatinine

Creatinine Clearance

Normal Adult Value

5 - 25 mg/dl

0.5 - 1.5 mg/dl

85 - 135 ml/min

Geriatric Value

8 - 28 mg/dl or slightlyhigher

0.6 - 1.2 mg/dl

Formula

Implications

↓: Liver damage, low protein diet, overhy-dration, malnutrition↑: Dehydration, high protein diet, GI bleed-ing, pre-renal failure

↓: None for older adult↑: Renal failure, shock, leukemia, SLE,acute MI, CHF, diabetic neuropathy

↓: Mild-to-severe renal impairment, hyper-thyroidism, amyotrophic lateral sclerosis,thiazide use↑: Hypothyroidism, renal-vascular hyper-tension

Source: Brigden & Heathcote, 2000; Engelberg et al., 2000; Kennedy-Malone et al., 2004.

Creatinine clearance = (140 - age in years) x (body weight in kilograms)(72 x serum creatinine in mg/dl)

Table 5.Estimating Creatinine Clearance Values for Men



to perform a creatinine clearanceon the older patient, a formulacan be used to estimate creati-nine clearance values. For men,the formula is shown in Table 5(Brigden & Heathcote, 2000). Forwomen, the value determined

from the formula is multiplied by0.85. Normal ranges for creatinineclearance are 104 to 140ml/minute for men and 87 to 107ml/minute for women (see Table4). Nurses should not assumethat all changes in renal function

are due to aging. Chronic urinarytract infections, benign prostatichypertrophy, prostatic tumors,and diabetic neuropathy are alsocauses and should be ruled out(Lewis et al., 2004).

Hepatic enzymes. The aging

Table 7.Geriatric Laboratory Values and Interpretations of Blood Lipids

Test

Cholesterol

High-DensityLipoproteins(HDL)

Triglycerides


Female (F)

<200 mg/dl

M >45 mg/dlF >55 mg/dl

M 40 - 160 mg/dlF 35 - 135 mg/dl

Geriatric Value

M may increase by 30mg/dl F may increase by 55mg/dl

M increases by 30%between ages 30 and 80F decreases by 30%between ages 30 and 80

M increases by 30%F increases by 50%

Implications

↓: Hyperthyroidism, starvation, malnutri-tion, anemia↑: Acute MI, atherosclerosis, uncontrolleddiabetes mellitus, hypothyroidism, biliaryobstruction, cirrhosis

↓: Chronic obstructive lung disease↑: Acute MI, hypothyroidism, diabetesmellitus, multiple myeloma, high-fat diet

↓: Hyperthyroidism, hyperparathyroidism,protein malnutrition, exercise↑: Acute MI, hypertension, hypothyroidism,nephritic syndrome, alcoholic cirrhosis,pancreatitis, high-carbohydrate diet

Source: Brigden & Heathcote, 2000; Kee, 2002

Table 8.Geriatric Laboratory Values and Interpretations of Glucose, Selected Electrolytes

Test

Serum Glucose

Calcium

Potassium

Normal Adult Value

70 - 110 mg/dl

4.5 - 5.5 mEq/l

3.5 - 5.3 mEq/l

Geriatric Value

70 - 120 mg/dl

No change

Slight increase

Implications

↓: Hypoglycemia, cancer (stomach, liver),malnutrition, alcoholism, cirrhosis of liver↑: Diabetes mellitus, adrenal gland hyper-function, acute MI, stress, crushing injury,renal failure, cancer (pancreas), CHF

↓: Diarrhea, lack of calcium intake, chronicrenal failure, alcoholism, pancreatitis↑: Hyperparathyroidism, malignant neo-plasms (bone, lung, breast, bladder, kid-ney), malignant myeloma, prolongedimmobilization, multiple fractures, renal calculi

↓: Vomiting, diarrhea, dehydration, malnu-trition, starvation, stress, diabetic acidosis↑: Acute renal failure, acidosis (metabolic orlactic), crushing injury, Addison’s disease

Source: Kee, 2002; Kennedy-Malone et al., 2004; Martin et al., 1997; Tripp, 2000



process does not significantlyinfluence most hepatic laborato-ry test values (for example, biliru-bin, ammonia, and lipids.) Whilelactic dehydrogenase (LDH) isnot affected by aging, theenzymes gamma-glutamyl-trans-ferase (GGT), serum aspartateaminotransferase (AST, SGOT),and alkaline phosphatase areaffected (Brigden & Heathcote,2000). GGT levels increase withaging (Tietz, Shuey, & Wekstein,1997). AST increases slightly forindividuals 60 to 90 years of ageto 18 U/L to 30 U/L (Tietz et al.,1997). Serum alanine aminotrans-ferase (ALT, SGTP) levels peakabout 50 years of age and gradu-ally fall to levels below those ofyounger adults by age 65 (Kelso,1990). Alkaline phosphate (AP)increases with age to a level of 30U/L to 140 U/L and is associatedwith age-related malabsorption,bone disorders, or decreasedliver or renal functioning(Brigden & Heathcote, 2000) (seeTable 6).

Lipid profile. Lipid-relatedchanges in aging adults youngerthan 70 years old are initiallynoted as increases in cholesterol,high-density lipoproteins (HDL),very low-density lipoprotein (VLDL),and triglycerides. Serum cholesterolincreases as much as 40 mg/dl byage 60 in men and age 55 in women(Brigden & Heathcote, 2000). Noincrease is seen in adults over 90years old; in fact, some very old

adults will have decreased choles-terol levels (Tietz et al., 1997).The mean HDL increases 30% inmen but decreases 30% in womenbetween ages 30 and 80 (Brigden& Heathcote, 2000). Triglyceridelevels increase by 30% in men and50% in women between the agesof 30 and 80 years (see Table 7).

Glucose. Serum glucose levelsincrease slightly but steadily withage in parallel with a decrease inglucose tolerance. The normalreference range for serum glu-cose is broader for older adults,from 70 mg to 120 mg/100 ml(Tripp, 2000) (see Table 8). Olderindividuals may have lower glu-cose levels, reflecting poor nutri-tional status or overall loss inbody mass (Kennedy-Malone etal., 2004). However, higher seruminsulin levels are more commonlyseen in older adults and may sug-gest insulin resistance, which isresponsible for impaired glucosetolerance in 25% of individualsover age 75 (Kennedy-Malone etal., 2004). If insulin receptors donot respond to the same fastinglevel of glucose in old age as theydid when the patient wasyounger, glucose intolerancewithout insulin-secretion changescould be the explanation. A refer-ence value for the 2-hour post-prandial glucose tolerance bloodsugar test (PPBS) is calculatedwith the following formula(Brigden & Heathcote, 2000):• 2-hr PPBS (mg/dl) = 100 + age

in years (for patients over age40)Serum electrolytes. In most

reports, electrolyte values remainwell within the standard refer-ence values for older adults.Calcium levels increase in olderpatients (ages 60 to 90) butdecrease in the very old over age90 (Martin, Larsen, & Hazen,1997). The initial increase can beexplained by a decrease in serumpH and an increase in parathyroidhormone levels found in olderindividuals (Tietz et al., 1997). Ifthe individual has a low serumalbumin, however, the serum cal-cium level will most likely be lowas mentioned previously. Serumpotassium has been reported toincrease slightly with age(Kennedy-Malone et al., 2004);however, most researchers usethe same reference values as foryounger adults (see Table 8).

Arterial blood gases (ABGs).Reference values for ABGs differin older adults from those ofyounger adults. Stiffening of theelastic lung structures, decreasednumber of functioning alveoli,and decreased strength of thediaphragm are age-related changesthat decrease respiratory function-ing (Martin et al., 1997). Thedecreased respiratory functioningresults in a decrease in the partialpressure of arterial oxygen ten-sion (PaO2). The arterial pressuredecreases approximately 5%every 15 years starting at age 30

Table 9.Geriatric Laboratory Values and Interpretations of Selected Blood Gases

Test

PaO2

PaCo2

Normal Adult Value

75 - 100 mmHg

35 - 45 mmHg

Geriatric Value

100.1 - (0.325 x age)

2% per decade

Implications

↓: Emphysema, pneumonia, pulmonaryedema↑: Hyperventilation

↓: Hyperventilation↑: COPD

Source: Brigden & Heathcote, 2000; Kee, 2002; Martin et al., 1997



(Brigden & Heathcote, 2000). Aformula (Brigden & Heathcote,2000) has been devised to esti-mate arterial oxygen in olderadults: • PaO2 (mmHg) = 100.1 – (0.325

X age in years)Additionally, a corresponding

increase in the carbon dioxidepressure (pCO2) of approximately2% per decade occurs after age50. The bicarbonate-ion concen-tration also increases with age,balancing out the pO2 and main-taining a normal blood pH(Brigden & Heathcote, 2000) (seeTable 9).

Thyroid function tests.Changes in thyroid function in theolder adult may be the most chal-lenging problem for nurses asthey try to separate disease fromaging changes. Hypothyroidism isseen in 2% to 6% of the generalpopulation over age 70 (Kennedy-Malone et al., 2004). Free thyrox-ine (FT4) levels decrease progres-sively with age (Kennedy-Malone

et al., 2004). Triiodothyronine(T3) shows substantial decreasesin ages 30 to 80 years. Typically, a20% change in T3 occurs duringthe lifetime of the older adult(Beers & Berkow, 2000) (seeTable 10).

Prostate-specific antigen (PSA).Relevance of PSA values to sup-port aggressive treatment is con-troversial (National Cancer In-stitute, 2004). Because an eleva-tion in the PSA could be indicativeof benign prostatic hypertrophyor prostate cancer, results fromthis test alone should not drivetherapy. Because of false posi-tives and false negatives, the age-relation variation of PSA increasesdifficulty in treatment decisions.Reference ranges for PSA with ageare (a) 60 to 69 years: 0.0 to 5.0ng/ml, and (b) 70 to 79 years: 0.0to 6.3ng/ml. Men who have had aradical prostatectomy are expect-ed to have values of 0.0 to 0.3ng/ml (Daniels, 2002) (see Table10).

ImplicationsLaboratory test results in-

form health care providers of apatient’s changing condition. Thepresence of multiple diseases, aswell as the incidence of polyphar-macy, may be a source of confu-sion in the clinical interpretationof laboratory results. Often, nurs-es must ask, “What test resultsare significant and suggest thepresence of disease? Whichresults suggest changes in patientconditions that require furtherassessment or interventions?”Greater understanding of how tointerpret laboratory test values inrelation to the clinical picture forthe older adult allows nurses toprovide age-appropriate assess-ments and interventions.

Mr. Doe’s laboratory reportsillustrate the confusion surround-ing evaluating laboratory data forthe older adult. Are his diagnostictest results helpful in explaininghis fatigue and weakness? Whatreally is happening with him?

Table 10.Geriatric Laboratory Values and Interpretations of Thyroxine, Triiodothyronine, Prostate-Specific Antigen

Test

Thyroxine (T4)

Thyroid-StimulatingHormone TSH)

Prostate-SpecificAntigen (PSA)


Female (F)

4.5 - 11.5 µg/dl

0.5 - 5.0 µlU/ml

PSA 1.45 ng/ml

Geriatric Value

3.3 - 8.6 µg/dl

Slight increase

Ages 50 - 59: 0.0 - 2.45ng/mlAges 60 - 69: 0.0 - 5.0ng/mlAges 70 - 79: 0.0 - 6.3ng/mlPost-radical prostatecto-my 0.0 - 0.3 ng/ml

Implications

↓: Hypothyroidism, protein malnutrition,corticosteroids↑: Hyperthyroidism, viral hepatitis, thyroiditis, myasthenia gravis

↓: Excessive thyroid hormone replacement,Graves’ disease, primary hyperthyroidism↑: Primary hypothyroidism, thyroid hormone resistance

↑: Prostate cancer, benign prostatic hyperplasia

Source: Beers & Berkow, 2000; Daniels, 2002; Kee, 2002



Perhaps the slightly elevatedrenal function tests indicate nor-mal changes of aging. However,they also might be due to proteinmalnutrition, which is suspectedbecause of his low body weightand recent weight loss. Obtainingserum protein and urinary creati-nine studies as well as a thoroughnutritional assessment mightassist in defining the diagnosis.

Interpretation of laboratorytest results allows nurses to ruleout diagnoses that are not perti-nent, but also assists in the exam-ination of a broad spectrum ofpossibilities. Each laboratorymay have variations in the refer-ence ranges due to techniquesand equipment. Nurses mustwork closely with laboratory per-sonnel and pathologists to beinformed about changes in refer-ence ranges for older adults in aspecific laboratory. Nurses alsoshould educate other health careprofessionals about age-relatedvariations in acceptable laborato-ry values. Better understandingof interpretation of diagnostictest results in older adults willallow nurses to feel confidentabout the care they provide. ■

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