List three factors that can influence the accuracy of the test

In 2013 we publimelted an post entitled “Best tests?” (Best Tests 18; Feb, 2013). In this post we tested clinicians to consider whether they can improve the strategy and manner in which they research laboratory investigations. To put it simply, it is around picking the best test, at the right time, for the right patient. After making the decision that an investigation is necessary, and choosing the most correct test, consideration should be offered to what components are present that might influence the interpretation of outcomes, or even the decision to continue with the test at that time.


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In many kind of scenarios, a diagnosis is based mainly on the patient’s history, via sustaining evidence from physicalexamination and laboratory investigation. Diagnosis is hardly ever based upon the results of laboratory investigations alone,and also experimentation is not always the best clinical course of action. Consideration requirements to be provided to whether testing willinclude meaningful indevelopment to the all at once clinical photo, and also then to the factors which may must be taken into accountonce interpreting the outcome. Can the test be done automatically or is the patient required to prepare in some means, e.g.fasting? Is the patient taking any type of medications that may influence or invalidate the outcomes, e.g. taking antibiotics priorto faecal antigen trial and error for Helicobacter pylori? Does the test need to be percreated at a details time,e.g. measuring testosterone in the morning? Is the test being done at the appropriate stage of illness, e.g. testing for antibodiesafter seroconvariation has occurred? A test result returned from the laboratory will certainly usually incorporate a recommendation variety ora thressarkariresultonline.infoanize worth based on guidelines. However, this outcome “on paper” does not constantly recurrent the clinical significanceof a test, which is just apparent once all various other factors for that individual patient have actually been taken into account.

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This post is not intfinished to be an extensive guide, but fairly an introduction of general principles to guide cliniciansin considering the wide range of factors that deserve to influence laboratory investigations or interpretation of results.

If you are unspecific about just how a test might be influenced by a certain factor you have actually figured out, discuss this through theexperimentation laboratory first, or encompass this information on your investigation research form.


To test or not?

Considerations prior to requesting a laboratory examination include:

What is my factor for requesting this test? E.g. am I investigating symptoms and signs? Am I monitoring a diseaseor impact of a medicine? Is this a screening test? Has this test currently been done? Does it should be repeated? If so, when? Will the test enhance patient (or in some cases, family members or partner) care? Is this the best test or combination of tests for the clinical situation? Is it the appropriate time to carry out the test? How must the sample be taken? How must the sample be stored and transported? How will certainly the test outcome be interpreted? How will the test result affect patient management? What will be the aftermath of a false positive result? Are tbelow potential damages of doing this test? How will certainly the patient be indeveloped of the result?

Biological variation


There are specific variations in laboratory test results that have the right to be meant due to non-modifiable sarkariresultonline.infoanic determinants,such as age, sarkariresultonline.infoanic rhythms and physiological alters in the time of pregnancy. These factors might be controlled for, e.g.by choosing the many appropriate time in the day, month or year for a test, or may be taken right into consideration in theinterpretation of outcomes, e.g. different referral varieties or thresholds for clinical meaning depending upon age, sexor pregnancy condition.


Advancing age

The physiological alters connected via ageing, in addition to raising co-morbidities and also polypharmacy, mean that oldercivilization are more most likely to have actually test results that loss external of the normal reference selection. For some tests, laboratoriesare able to carry out an age-adjusted referral variety, but for other tests, a result external of the range in an older patient,demands to be construed in the context of their overall clinical picture.

In many kind of cases, assessing the rate and magnitude of readjust over time offers more information than interpreting the valueof an individual result. Often the populace variety of a test mirrors a lot more variation than that for an individual patient,e.g. serum creatinine, liver enzymes. In such situations the patient’s own previous outcomes are a valuable baseline.

An instance of the result of age, sex and also other variables on interpretation of laboratory outcomes is serum alkaline phosphatase(ALP), which might be requested as component of liver function tests. The top referral limit is markedly boosted duringpuberty as this is the time of maximum bone remodelling. After this duration ALP levels fall to a brand-new upper limit throughyounger adult life, and also then increase again, particularly in females around the time of perimenopausage, mostly reflectinga boost in bone turnover at that time. Marked increases in serum ALP might likewise occur in womales in late pregnancy (dueto manufacturing of ALP by the placenta), and during various other times such as in the weeks after healing of a fracture.

Another example of laboratory values which readjust with age is lipids. In adults, complete cholesterol, LDL and triglyceridelevels boost with age, until about age 50 to 60 years in males and age 60 to 70 years in females, once theybegin to decline in a lot of people; triglyceride levels tend to continue to increase in older females.1 Manylaboratories are no longer reporting recommendation varieties for lipid levels, as this is thought about much less clinically useful thantherapy targets based upon the underlying reason of increased levels and also cardiovascular danger.2

When interpreting laboratory results in an older patient, ensure that an age-appropriate reference selection is supplied if accessible. Normal age-connected alters, e.g. degradation in renal feature, may explain outcomes exterior of the recommendation selection in an older patient, however age alone need to not be thought about as the just cause of an abnormal outcome.


Biological rhythms

Many type of laboratory parameters vary depending upon the moment of day, week, month or year once they are sampled. Body temperature,hormone production (e.g. cortisol, testosterone), platelet and cardiac attribute and also cognitive function follow a circadian(24 hour) rhythm.1 To allow for this impact, some laboratory tests are recommended at particular times of theday, e.g. testosterone have to be sampled in between 7 am – 10 am. This is because peak testosterone levels normally occurin the beforehand morning; evening levels are often considerably (approximately 50%) lower, specifically in younger males.2 Forthe majority of purposes, serum cortisol* must preferably be sampled in the at an early stage morning as tbelow is marked diurnal variation,through beforehand morning levels at leastern 50 – 100% greater than levels in the late afternoon.2

Testing vitamin D levels (25-hydroxyvitamin D) is hardly ever necessary, but, if levels are obtained, they must beconstrued in the conmessage of the moment of year they are sampled. Seasonal variations happen through vitamin D, with the lowestlevels commonly oboffered at the finish of winter (in countries through characterized periods, such as New Zealand). For instance, ifa patient has actually a mild vitamin D deficiency at the finish of winter, this is most likely to be less clinically substantial thana patient via a mild deficiency at the finish of summer.

For further information, view “Age-related testosterone decline inmales” Best Tests (Jun, 2012) and “Vitamin D supplementation:navigating the debate” BPJ 36 (Jun, 2011).

* Serum cortisol levels have actually a vast referral range, and also therefore this is a reasonably inaccurate measure of cortisol excess or deficiency. The dexamethasone suppression test is supplied to aid exclude Cushing’s syndrome and also the Synacthen stimulation test is offered to investigate for main or additional hypoadrenalism.2

Menstrual cycle

Females who are menstruating have actually predictable monthly rhythms of FSH, LH, oestrogen and also progesterone. In a basic practicesetting, these hormone levels may be asked for to investigate conditions such as oligo/amenorrhoea or sub-fertility. Theinterpretation and meaningfulness of the results is dependent not just on the value, but on the phase in the cycle whenthe hormone was measured.

In a normal menstrual cycle LH levels height mid-cycle to create ovulation. FSH levels likewise top mid-cycle. Oestradiol(the preleading oestrogen in woguys that are ovulating) is highest prior to ovulation, and also then reduces if fertilisationdoes not occur. Unmuch less ovulation is being investigated, levels of these hormones are ideal measured beforehand in the menstrualcycle.2

N.B. Investigation of oestradiol levels is not beneficial in woguys who are taking oestrogen-containing oral contraceptivesas this suppresses the pituitary ovarian axis. LH and also FSH are also suppressed in women taking depot progesterone.2

Progesterone levels top in the second phase of the menstrual cycle, after ovulation has developed, to prepare the endometriumfor implantation of an embryo. Progesterone levels are occasionally measured to establish if ovulation has occurred; usuallyseven days before the intended day of menstruation, i.e. around day 21 if the woman has actually a continual 28 day cycle.

Oestradiol levels decrease and FSH levels increase throughout menopause, however monitoring these hormone levels is not alwaystrusted in predicting once a womale is entering menopause, as fluctuations occur with varying ovarian activity.

For further information, check out “Reabundant hormones: the ideal testat the ideal time, for the appropriate patient” Best Tests (Feb, 2013).


Pregnancy

Physiological alters during pregnancy bring about alterations in many laboratory parameters, such as blood volume, liverand also renal function and hormone levels (Table 1, over page). Reference arrays for various steras of pregnancy are availablefor some laboratory tests, but, these arrays are often not also characterized as the general recommendation selection. In addition,pregnancy-connected alters, such as alterations in binding proteins, can impact asstates differently, e.g. cost-free hormone levelshave the right to be assay dependent. As such caution is recommfinished in interpreting results based on referral arrays and the laboratoryshould be contacted if tbelow is any kind of doubt.

When requesting a laboratory investigation in a woman that is pregnant, note the gestational week on the laboratoryrepursuit develop.


Table 1: Examples of laboratory values that readjust via pregnancy1, 2, 3

IncreasesDecreases
Alpha-fetoprotein (AFP); peaks in third trimesterHaemoglobin; as a result of haemodilution led to by higher blood volume
Alkaline phosphatase (ALP); approximately four fold increase in third trimesterFerritin; decreases as pregnancy progresses
Blood volume (suppose plasma volume); rises by 30–50%FT4; may decrease slowly in late pregnancy (deserve to be assay dependent)
Lipids; as much as 40% increase in cholesterol, triglyceride levels can markedly rise in some women (due to theimpact of oestrogen)Prothrombin and also partial thromboplastin times
Creatinine clearance; glomerular filtration rate increases 40-60% (eGFR cannot be reliably calculated)TSH; decreases initially trimester, then returns to normal (as a result of the result of hCG)
ESR; increasing to 30–60 mm/h as pregnancy progressesSodium; slight decrease due to transforms in blood volume and liquid homeostasis
Hormones; oestrogen, testosterone, progesterone, huguy chorionic gonadotrophin (hCG), prolactin
Iron binding (transferrin levels); substantial rise also in a non-iron deficient woman (as a result of the effectof oestrogen)
White blood count; might rise to 15–18 x109/L

Reference selection

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A reference selection for a laboratory test is a statistically-derived numerical variety of outcomes that is acquired by testinga sample of “healthy” individuals. Defining “healthy”, however, is not straightforward, and counts on a vast range ofdeterminants and assumptions; in many type of cases to define a variety sindicate using “perfectly healthy” patients would make it unrealisticand unusable.

The variety is also frequently assumed to have actually a Gaussian circulation, in that 68% of worths lie within one traditional deviation(SD) of the mean value, 95% within 2 SDs and also 99.7% of worths within 3 SDs.1 However, many varieties perform not have a Gaussiandistribution, but quite the upper end of the distribution is skewed. In these instances the range can be acquired either bylog transformation of the data, or simply by identifying the pertinent 2.5th and 97.fifth percentiles in the population beingstupassed away (with attempts to exclude those patients likely to have an underlying pathology by clinical, laboratory and statisticalmeans).

Reference arrays for laboratory results normally encompass 2 SDs from the intend worth meaning that one in 20 “healthy”people will certainly have a test outcome outside the reference variety.1 Reference varieties vary between laboratories, and also canchange if brand-new proof becomes easily accessible. The upper and also lower borders of the array are not absolute and also carry out not define “normal”and “abnormal”, however are points at which the probability of clinical definition often tends to increase.

Some “referral ranges” are based upon references from international bodies for optimising patient outcomes, ratherthan on a population statistical circulation. For example, the upper reference limit for TSH in at an early stage pregnancy is basedon guidance statements from the Endocrine Society and the Amerideserve to Thyroid Association. The recommended limit for serumuric acid in patients taking uric acid lowering therapy (0.36 mmol/L) is based upon the European sarkariresultonline.infoanization against Rheumatism(EULAR) guidelines.

Interpretation of an outcome outside the stated recommendation selection is therefore very dependent on the clinical backgroundof the patient, the pattern of other abnormalities, and the clinical question(s) being asked.


Diet and also nutritional status

Fasting, calorie restriction, food exemption diets, malnutrition and also dehydration have the right to all influence laboratory results.The definition of some laboratory tests is dependent on managing dietary components, e.g. ensuring there is sufficientgluten in the diet for at least several weeks prior to serology investigations for coeliac disease, or fasting prior toassessing the impact of intervention in a patient through formerly high triglyceride levels. In various other scenarios, assessingdietary components deserve to assist to interpret unintended laboratory outcomes, e.g. a vegetarian or vegan diet can bring about decreasedlevels of vitamin B12, a low carbohydprice diet can cause increased ketone levels (as part of urinalysis) and a high proteindiet can result in raised uric acid levels.

Fasting for 12 hours prior to laboratory experimentation might be useful or even necessary, depending upon theclinical scenario, to obtain the a lot of accurate result for the complying with tests, which are affected by the ingestion of certainfoods:4

Glucose; only if shown – for many patients HbA1c is currently recommended as the test of first alternative forthe diagnosis and also security of type 2 diabetes, and also does not need fasting Triglycerides; for a lot of patients fasting is not required for lipid experimentation, yet might be helpful for security in peoplevia high triglyceride levels Uric acid; fasting is not generally forced in practice to get accurate results however the effect of recent dietary intakemay help to explain unsupposed resultsCreatinine; a current meal via high meat content have the right to have actually a far-reaching influence on serum creatinine, and this shouldbe considered when security eGFR5

Sustained low caloric intake and also starvation can result in numerous transforms to laboratory parameterssuch as glucose, thyroid feature, electrolytes, liver feature, renal function and also lipids.4 Uric acid levelsmay be enhanced as a result of ketonaemia (bring about diminished clearance).3

Malnutrition has differing effects on laboratory outcomes, depending on the nature of the patient’s nutritionalstanding. Malnutrition is classically assumed of as a deficiency of protein and energy, via or without micronutrient deficiencies.However, malnutrition might be identified as under-nutrition, over-nutrition or deficiency of specific nutrients. Malnutritionhave to be thought about as a reason for outcomes such as lessened ferritin, folate and vitamin B12 levels.

Dehydration have the right to be taken into consideration as a reason of sodium and also potassium imbalances, and deserve to alsoaffect many other indices, such as creatinine and also urea, albumin, lipids and haematology indices.

See more: Theorists Who Believe Poverty Is Relational Measure Poverty By Determining:

For better information see: “A major care method to sodiumand also potassium imbalance”, Best Tests (Sep, 2011) and“Strategies to enhance nutrition in elderly people”, BPJ Special Edition (May, 2011).

Caffeine

The impact of caffeine on laboratory parameters has not been fully stupassed away. It has a brief fifty percent life of three to sevenhrs, but this varies among people.4 Caffeine intake reasons transient rises in blood glucose levelsand impairs glucose tolerance.3, 4 It can also influence other specialised investigations such as interpretationof metanephrines once investigating hypertension.


Alcohol

The result of alcohol usage on laboratory investigations relies on the duration and level of usage. Acute (transient)results of alcohol usage (within 2 to four hours) encompass reduced serum glucose and also raised plasma lactatevia a reduction in urinary uric acid excretion as a result of the inhibition of hepatic gluconeogenesis.3

Chronic results of alcohol usage on laboratory investigations include:2

Elevated gamma glutamyl transferase (GGT) and also mean cell volume (MCV) which are generally used to test for excessivealcohol usage Elevated aspartate aminotransferase (AST), alanine aminotransferase (ALT) and also AST/ALT proportion Elevated triglyceride levels Elevated uric acid and also ferritin levels as a result of fatty liver and also alcoholic hepatitis Elevated creatine kinase due to alcoholic myopathyOther haematological abnormalities, e.g. anaemia and thrombocytopenia

Alcohol consumption deserve to also add to vitamin and also mineral deficiencies as a result of replacement of food through alcoholor as a result of interference of absorption of vitamin and also minerals, e.g. decreased folate, vitamin A, vitamin B andcalcium levels.


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Timing of investigation in relation to phase of illness

The definition of an investigation can be dependent on once the sample was taken in relation to the phase of the diseaseprocedure. The phase of disease have the right to also influence the selection of the many proper examination. For example, a serologytest for syphilis may be falsely negative if the sample is taken also early after exposure, and also therefore seroconversionhas actually not yet arisen. Different kinds of serology test will certainly carry out information around active or previous infection.

Acute disease have the right to likewise affect the outcome of some investigations, e.g. ferritin is an acute phase protein and levelscan be boosted by inflammation and infection, and also chronic disease and malignancy.


Tobacco smoking

Regular cigarette smoking and expocertain to nicotine deserve to have actually both acute and chronic impacts on laboratory investigations, althoughthe mechanisms behind these changes are not completely interpreted. Within one hour of cigarette smoking one to five cigarettes, plasma/serumconcentrations of fatty acids, adrenaline, glycerol, aldosterone and cortisol are raised.3 People that arechronic smokers might have actually persistent boosts in leukocyte counts, hefty steels, lipoproteins, tumour markers and haematocrit(PCV), and also decreases in the activity of some enzymes (e.g. angiotensin-converting enzyme).3


Exercise

The effect of exercise on laboratory parameters is dependent on the health condition of the patient, air temperature duringexercise and also intake of food and water in the time of or adhering to exercise.4 Extreme exercise or vigorous exercisein a person unaccustomed to this level of task have the right to lead to changes to some laboratory parameters. For instance, themany prevalent cause of elevated creatine kinase (CK) levels is exercise. Intense exercise deserve to cause an elevation in CK levelsfor a number of days to a week. Well-muscled civilization regularly have actually CK levels persistently over normal.2

Thyroid attribute is also known to be transformed in people undergoing high-intensity exercise. For instance, anaerobic exerciserises TSH and also FT4 levels, but decreases FT3.4 Liver feature (AST and to a lesser extent ALT) tests canboost after exercise. Transient proteinuria and also haematuria are additionally prevalent after exercise, yet usually solve aftera few days. Other analytes that have the right to be enhanced by exercise include urea, creatinine, lactate dehydrogenase, prothrombintime, and D-dimer levels. Fibrinogen and also the activated partial thromboplastin time (APTT) deserve to be diminished.4 Mostof these results are most likely to be transitory (e.g. persistent for a couple of hrs to a few days after exercise), yet thisrelies on individual patient factors.


Medicines

The medicines that a patient is taking can considerably affect some laboratory results, therefore this demands to betaken into consideration when interpreting outcomes. It is good practice to note the relevant medicines that a patientis taking on the laboratory repursuit develop, especially if they might possibly influence results, e.g. antihypertensivesbeing taken when investigating secondary reasons of hyperstress and anxiety or hormone replacement treatment being taken when requestingendocrine tests.

Medicines deserve to have actually a direct effect on the sample or laboratory experimentation process, resulting in an inaccurateresult. For example, as soon as investigating for H. pylori, a false-negative outcome of a faecal antigen test may occurin patients taking a course of antibiotics or proton pump inhibitors (PPIs) as this would certainly decrease the gastric load of H.pylori.

Medicines might likewise reason a biological effect to the patient which would account for an changed outcome.For example, some antibiotics (e.g. cotrimoxazole and also erythromycin), cardiovascular medicines (e.g. amiodarone and also propranolol),NSAIDs (e.g. piroxicam) and gastrointestinal medicines (e.g. omeprazole) might account for a increased INR bring about a patienttaking warfarin that typically has a steady INR.2 Long term usage of metformin or PPIs is a possible explanationfor a low vitamin B12 level.2 Many type of medicines have an effect on the balance of sodium and potassium in the body,e.g. diuretics may reason hypernatraemia (specifically loop diuretics), hyponatraemia (especially thiazides), hyperkalaemia(specifically potassium-sparing diuretics) and hypokalaemia (loop and thiazide diuretics).2

For additionally indevelopment, see: “Amain treatment strategy to sodium and also potassium imbalance”, Best Tests (Sep, 2011).

When surveillance the serum concentration or result of a medication, the laboratory test demands to be timedrelying on the drug’s metabolism, e.g. a blood sample for testing lithium levels need to be gathered 10–14 hours afterthe last dose and also a sample for testing digoxin must be gathered at leastern eight hrs after the last dose.2 Wheninitiating a patient on warfarin, INR levels should be sampled daily in the morning, after an evening dose of warfarin,to calculate vital dose adjustments.2


Analytical variation occurs because of imperfections in testing approaches and devices, which might reason analyte worths tobe slightly different each time they are measured. Modern trial and error approaches and laboratory equipment expect that analyticalvariation is usually less of a factor in differing test results than biological variation. Ideally the variation in measurement(expressed as analytical coefficient of variation, or CVa) must be much less than fifty percent the individual patient biologicalvariation of the analyte in question (CVi).

For even more indevelopment on variation via certain analytes, see: www.westgard.com/biodatabase1.htm


Collection, storage and move of samples

If a sample is being accumulated at the exercise, it is important to be acquainted with the type of collection containerand sample tool that is forced by the laboratory for the particular test, as this deserve to affect outcomes, periodically markedly.For example, a swab for PCR testing for pertussis have to be transported in a dry tube or a tube with global viral transportmedium, yet not in a tube with charcoal move medium (which is acceptable for swab culture).

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Other examples of collection or transfer requirements for optimal test outcomes include:

Blood samples for coagulation researches, including platelet count, D-dimer, prothrombin time, APTT and also fibrinogen,must be transported to laboratory within 4 hours of collection6 Urine specimens for society should be stored in a fridge before transport to alleviate the rate of multiplicationof microsarkariresultonline.infoanisms Samples for glucose analysis should be separated as shortly as possible after collection; this uses also with samplesgathered in fluoride or oxalate arsenal tubes, as reduction in glucose concentration still occurs for60–90 minutes Samples for potassium or phosphate have to not be left overnight, specifically in the fridge, as outcomes have the right to be markedlytransformed, e.g. late evening arsenal via delayed deliver to the laboratory Faecal samples for society and also microscopy should preferably be transported to the laboratory within 4 hoursSemen samples for fertility trial and error should be maintained by the patient at body temperature, e.g. by storing in a clothingpocket, and transported to the laboratory within one hour of arsenal.2 The exact same level of urgency is notcompelled for post-vasectomy seguys evaluation.

Refer to your local laboratory for specimen arsenal demands. Some suppliers have actually online resources, e.g. www.labtests.co.nz/referrers/tests/collection-guide


Haemolysis

Haemolysis is the destruction of red blood cells, leading to release of haemoglobin and cellular constituents, e.g.potassium, right into the plasma. It is a reason of inexact blood test outcomes and also deserve to occur either in vitro duringarsenal, storage or transport of a blood sample or in vivo resulting in haemolytic anaemia if major.

In vivo and in vitro haemolysis have actually various analytical attributes, e.g. haptoglobin levelsare normal through in vitro haemolysis, therefore analysis have the right to disclose if haemolysis emerged in the time of the collectionof the blood sample or if it was currently present.2 The possibility of haemolysis have to generally be notedon results by the laboratory staff, including the most likely degree of interference and relicapacity of the outcome.If the haemolysis is significant, a rearsenal of the sample may be advised.

Several of the analytes that have the right to be affected when in vitro haemolysis has actually occurred include:2

Elevations in potassium, AST (ALT is much less affected), lactate dehydrogenase, phosphate Reductions in bilirubin, troponin T, insulin

Standardised sample repertoire and transport procedures can help to proccasion in vitro haemolysis, including:3

Allowing alcohol to dry entirely as soon as it is used for skin sterilisation prior to venepuncture Not leaving a tourniquet on for much longer than 2 minutes Using an as necessary sized needle for collection (20 – 22 gauge needles can be used for many regime collections) Not rerelocating the needle from the vein if the vacuum tube is attached Not exposing the specimales to extremes in temperature Avoiding vigorous mixing or shaking of tubes Avoiding delay in sending samples to the laboratory

Acknowledgement

Thank you to Dr Cam Kyle, Chemical Pathologist, Auckland for skilled evaluation of this article.

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References

Kyle C (Ed). Pathology handbook: a overview to the interpretation of pathology tests. New South Wales: Sonic Healthtreatment, 2014. Guder WG, editor. Samples: from the patient to the laboratory: the influence of preanalytical variables on the qualityof laboratory outcomes. third, rev ed. Weinheim, New York: Wiley-VCH, 2003. Peck Palmer OM. Effect of age, gender, diet, exercise and ethnicity on laboratory test outcomes. In: Accurate resultsin the clinical laboratory: a guide to error detection and also correction. London; Waltham, MA: Elsevier, 2013. pp.9–17. Priess D, Godber I, Lamb E, et al. The influence of a cooked meat meal on estimated glomerular filtration rate. AnnClin Biochem 2007;44:35–42.