Artifactual elevation of measured plasma L-lactate concentration in the presence of glycolate

Suggested guide to using lactate gap as a surrogate marker in the diagnosis of ethylene glycol overdose

BackgroundEthylene glycol (EG) poisoning, if not diagnosed rapidly, can lead to poor patient outcomes. Gas chromatography (GC) is primarily used for EG quantitation which is rarely available, and the turn-around time may be prolonged. Most lactate results from point-of-care (POCT) methods are falsely elevated in EG poisoning compared with automated chemistry analyser results. In combination, the lactate gap (POCT-Automated chemistry) can be used as surrogate marker in just about all laboratories to indicate likely EG toxicity and guide treatment.Case ReportA man presented by ambulance to hospital with severe agitation requiring mechanical ventilation to facilitate ongoing management. Venous blood gas analysis confirmed a high anion gap metabolic acidosis (HAGMA) with an elevated lactate. The lactate and osmolarity measured in the laboratory showed a normal lactate and high osmolarity, giving a large osmolar gap. The patient was immediately commenced on renal replacement therapy for presumed EG poisoning to minimize kidney injury, and the treatment continued for 19 hours. A very high EG concentration was confirmed by GC the next day.ConclusionAn elevated lactate gap along with a HAGMA and osmolar gap can provide rapid surrogate laboratory data indicating EG poisoning enabling timely treatment and better patient outcomes.

Extracorporeal treatment for ethylene glycol poisoning: systematic review and recommendations from the EXTRIP workgroup

Ethylene glycol (EG) is metabolized into glycolate and oxalate and may cause metabolic acidemia, neurotoxicity, acute kidney injury (AKI), and death. Historically, treatment of EG toxicity included supportive care, correction of acid-base disturbances and antidotes (ethanol or fomepizole), and extracorporeal treatments (ECTRs), such as hemodialysis. With the wider availability of fomepizole, the indications for ECTRs in EG poisoning are debated. We conducted systematic reviews of the literature following published EXTRIP methods to determine the utility of ECTRs in the management of EG toxicity. The quality of the evidence and the strength of recommendations, either strong ("we recommend") or weak/conditional ("we suggest"), were graded according to the GRADE approach. A total of 226 articles met inclusion criteria. EG was assessed as dialyzable by intermittent hemodialysis (level of evidence = B) as was glycolate (Level of evidence = C). Clinical data were available for analysis on 446 patients, in whom overall mortality was 18.7%. In the subgroup of patients with a glycolate concentration ≤ 12 mmol/L (or anion gap ≤ 28 mmol/L), mortality was 3.6%; in this subgroup, outcomes in patients receiving ECTR were not better than in those who did not receive ECTR. The EXTRIP workgroup made the following recommendations for the use of ECTR in addition to supportive care over supportive care alone in the management of EG poisoning (very low quality of evidence for all recommendations): i) Suggest ECTR if fomepizole is used and EG concentration > 50 mmol/L OR osmol gap > 50; or ii) Recommend ECTR if ethanol is used and EG concentration > 50 mmol/L OR osmol gap > 50; or iii) Recommend ECTR if glycolate concentration is > 12 mmol/L or anion gap > 27 mmol/L; or iv) Suggest ECTR if glycolate concentration 8-12 mmol/L or anion gap 23-27 mmol/L; or v) Recommend ECTR if there are severe clinical features (coma, seizures, or AKI). In most settings, the workgroup recommends using intermittent hemodialysis over other ECTRs. If intermittent hemodialysis is not available, CKRT is recommended over other types of ECTR. Cessation of ECTR is recommended once the anion gap is < 18 mmol/L or suggested if EG concentration is < 4 mmol/L. The dosage of antidotes (fomepizole or ethanol) needs to be adjusted during ECTR.

Ethylene Glycol Intoxication Requiring ECMO Support

Ethylene glycol is commonly used in antifreeze, and ingestion of even a small amount can result in acute kidney injury, severe metabolic acidosis, and neurological injury. When cases are recognized early, treatment involves administration of alcohol dehydrogenase inhibitors to prevent conversion to toxic metabolites of glycolate, glyoxolate, and oxalate. In later presentations with more severe renal injury, hemodialysis may be required for clearance of toxic metabolites and supportive care for renal failure. We present the first reported case of severe ethylene glycol intoxication requiring support of extracorporeal membrane oxygenation (ECMO) due to refractory cardiopulmonary collapse.

Clinical use of plasma lactate concentration. Part 1: Physiology, pathophysiology, and measurement

OBJECTIVE

To review the current literature with respect to the physiology, pathophysiology, and measurement of lactate.

DATA SOURCES

Data were sourced from veterinary and human clinical trials, retrospective studies, experimental studies, and review articles. Articles were retrieved without date restrictions and were sourced primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection.

HUMAN AND VETERINARY DATA SYNTHESIS

Lactate is an important energy storage molecule, the production of which preserves cellular energy production and mitigates the acidosis from ATP hydrolysis. Although the most common cause of hyperlactatemia is inadequate tissue oxygen delivery, hyperlactatemia can, and does occur in the face of apparently adequate oxygen supply. At a cellular level, the pathogenesis of hyperlactatemia varies widely depending on the underlying cause. Microcirculatory dysfunction, mitochondrial dysfunction, and epinephrine-mediated stimulation of Na⁺ -K⁺ -ATPase pumps are likely important contributors to hyperlactatemia in critically ill patients. Ultimately, hyperlactatemia is a marker of altered cellular bioenergetics.

CONCLUSION

The etiology of hyperlactatemia is complex and multifactorial. Understanding the relevant pathophysiology is helpful when characterizing hyperlactatemia in clinical patients.

Lactate Gap: A Diagnostic Support in Severe Metabolic Acidosis of Unknown Origin

Ethylene glycol poisoning is a medical emergency. The metabolites glycolate and glyoxylate give metabolic acidosis. Because of similar structure, these metabolites are misinterpreted as lactate by many point-of-care blood gas analyzers. The falsely high lactate values can lead to misdiagnosis, inappropriate laparotomies, and delayed antidotal therapy. As laboratory analyzers measure plasma lactate only, the difference or the “lactate gap” aids in early diagnosis. We present a patient with severe metabolic acidosis and elevated lactate levels on the point-of-care analyzer. A lactate gap supported the diagnosis of ethylene glycol poisoning. Hemodialysis and fomepizole treatment could be started immediately.

Recurrent Ethylene Glycol Poisoning with Elevated Lactate Levels to Obtain Opioid Medications

BACKGROUND

Malingering is when a patient feigns illness for secondary gain. While most patients with malingering manufacture or exaggerate symptoms, some patients may induce illness. Previous reports of malingering patients inducing illness include sepsis, kidney pain, migraine, and chest pain. However, acute poisoning as a manifestation of malingering appears to be rare.

CASE REPORT

We describe the case of a 39-year-old man who presented to the emergency department complaining of diffuse body pain. The patient reported multiple admission at outside hospitals for "lactate" and said, "it feels like it is happening again because of how my body feels." Laboratory findings were concerning for serum lactate of >20.0 mmol/L and ethylene glycol (EG) level of 19 mg/dL. A chart review found that the man had been admitted for elevated serum lactate 8 times to area hospitals in several years, often in the setting of EG poisoning. During these episodes he required intravenous fluids and frequent intravenous pain medications. When confronted about concern regarding the recurrent fallacious lactate levels in the setting of factitious EG ingestion, the patient often became combative and left against medical advice. The primary metabolite of EG, glycolic acid, can interfere with lactate assays, causing a false elevation. Our patient apparently recognized this and took advantage of it to be admitted and receive intravenous opioids. This is the only case known to us of malingering via EG ingestion. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Emergency physicians should be aware that metabolites of EG may interfere with serum lactate assay. In addition, they should be aware of possible malingering-related poisoning and plausible association with requests for intravenous opioid pain medications. This represents a risk to the patient and others if undiagnosed.

Lactate gap as a tool in identifying ethylene glycol poisoning

Ethylene glycol toxicity is a known cause of anion gap metabolic acidosis, with the presence of an osmolar gap and the right clinical context suggesting to the diagnosis. Rapid recognition and early treatment is crucial. Unfortunately, ethylene glycol levels are not readily available and must be performed at a reference laboratory. We present a case where recognising the significance of the 'lactate gap' assisted in identifying ethylene glycol poisoning.

Serum osmolal gap in clinical practice: usefulness and limitations

BACKGROUND

Although serum osmolal gap can be a useful diagnostic tool, clinicians are not familiar with its use in clinical practice.

OBJECTIVES

The review presents in a series of questions-answers and under a clinical point of view the current data regarding the use of osmolal gap.

DISCUSSION

The definition and the best formula used for the calculation of osmolal gap, the main causes of increased osmolal gap with or without increased anion gap metabolic acidosis, as well as the role of concurrent lactic acidosis or ketoacidosis are presented under a clinical point of view.

CONCLUSIONS

The calculation of osmolal gap is crucial in the differential diagnosis of many patients presenting in emergency departments with possible drug or substance overdose as well as in comatose hospitalized patients.

Ethylene Glycol Poisoning: An Unusual Cause of Altered Mental Status and the Lessons Learned from Management of the Disease in the Acute Setting

Ethylene glycol is found in many household products and is a common toxic ingestion. Acute ingestions present with altered sensorium and an osmolal gap. The true toxicity of ethylene glycol is mediated by its metabolites, which are responsible for the increased anion gap metabolic acidosis, renal tubular damage, and crystalluria seen later in ingestions. Early intervention is key; however, diagnosis is often delayed, especially in elderly patients presenting with altered mental status. There are several laboratory tests which can be exploited for the diagnosis, quantification of ingestion, and monitoring of treatment, including the lactate and osmolal gaps. As methods of direct measurement of ethylene glycol are often not readily available, it is important to have a high degree of suspicion based on these indirect laboratory findings. Mainstay of treatment is bicarbonate, fomepizole or ethanol, and, often, hemodialysis. A validated equation can be used to estimate necessary duration of hemodialysis, and even if direct measurements of ethylene glycol are not available, monitoring for the closure of the anion, lactate, and osmolal gaps can guide treatment. We present the case of an elderly male with altered mental status, acute kidney injury, elevated anion gap metabolic acidosis, and profound lactate and osmolal gaps.

Ethylene glycol poisoning: a rare but life-threatening cause of metabolic acidosis-a single-centre experience

Background.

Intoxication with ethylene glycol happen all around the world and without rapid recognition and early treatment, mortality from this is high.

Methods.

In our study, we retrospectively analysed six cases of ethylene glycol intoxication in our department. We measured ethylene glycol or glycolate levels, lactate levels and calculated the osmolal and anion gap.

Results.

Data from six patients admitted to the nephrology department between 1999 and 2011 with ethylene glycol poisoning are reported. All patients were men. The mean pH on admission was 7.15 ± 0.20 and the anion and osmolal gap were elevated in five of six patients. Four patients had an acute kidney injury and one patient had an acute-on-chronic kidney injury. All patients survived and after being discharged, two patients required chronic intermittent haemodialysis. Interestingly, at the time of admission, all patients had elevated lactate levels but there was no linear regression between toxic levels and lactate levels and no linear correlation was found between initial lactate levels and anion gap and osmolal gap.

Conclusions.

The initial diagnosis of ethylene glycol poisoning is difficult and poisoning with ethylene glycol is rare but life threatening and needs rapid recognition and early treatment. Therefore, intoxication with ethylene glycol should not be misdiagnosed as lactic acidosis in patients with metabolic acidosis and elevated lactate levels.

The 'gap' in the 'plasma osmolar gap'

Ethylene glycol poisoning is a medical emergency that presents challenges for clinicians and clinical laboratories. If left untreated, it may cause morbidity and death, but effective therapy is available if diagnosed in time. The diagnosis of ethylene glycol poisoning is not always straightforward and the commonly quoted 'plasma osmolar gap' is not sufficiently sensitive to exclude a small ingestion and has been reported to be normal in a number of serious exposures. The 'plasma osmolar gap' cannot distinguish among ethanol, isopropyl alcohol, methanol or ethylene glycol. Thus, the measurement of serum ethylene glycol and, ideally, glycolic acid, its major toxic metabolite in serum, is definitive. This also holds true for methanol and its metabolite formic acid. Ethylene glycol metabolites target the kidney and lead to reversible oliguric or anuric injury, which in turn slows the elimination of ethylene glycol. The therapeutic options include reversal of metabolic acidosis, inhibition of alcohol dehydrogenase and early haemodialysis.

Clinical use of lactate monitoring in critically ill patients

Increased blood lactate levels (hyperlactataemia) are common in critically ill patients. Although frequently used to diagnose inadequate tissue oxygenation, other processes not related to tissue oxygenation may increase lactate levels. Especially in critically ill patients, increased glycolysis may be an important cause of hyperlactataemia. Nevertheless, the presence of increased lactate levels has important implications for the morbidity and mortality of the hyperlactataemic patients. Although the term lactic acidosis is frequently used, a significant relationship between lactate and pH only exists at higher lactate levels. The term lactate associated acidosis is therefore more appropriate. Two recent studies have underscored the importance of monitoring lactate levels and adjust treatment to the change in lactate levels in early resuscitation. As lactate levels can be measured rapidly at the bedside from various sources, structured lactate measurements should be incorporated in resuscitation protocols.

Methanol and ethylene glycol intoxication

Accidental or intentional ingestion of substances containing methanol and ethylene glycol can result in death, and some survivors are left with blindness, renal dysfunction, and chronic brain injury. However, even in large ingestions, a favorable outcome is possible if the patient arrives at the hospital early enough and the poisoning is identified and appropriately treated in a timely manner. This review covers the common circumstances of exposure, the involved toxic mechanisms, and the clinical manifestations, laboratory findings, and treatment of methanol and ethylene glycol intoxication.

Ethylene glycol poisoning: quintessential clinical toxicology; analytical conundrum

Ethylene glycol poisoning is a medical emergency that presents challenges both for clinicians and clinical laboratories. Untreated, it may cause morbidly or death, but effective therapy is available, if administered timely. However, the diagnosis of ethylene glycol poisoning is not always straightforward. Thus, measurement of serum ethylene glycol, and ideally glycolic acid, its major toxic metabolite in serum, is definitive. Yet measurement of these structurally rather simple compounds is but simple. This review encompasses an assessment of analytical methods for the analytes relevant for the diagnosis and prognosis of ethylene glycol poisoning and of the role of the ethylene glycol metabolites, glycolic and oxalic acids, in its toxicity.

Serial measurement of lactate concentration in horses with acute colitis

BACKGROUND

Serial measurement of lactate concentration is utilized for therapeutic and prognostic purposes in human critical care. The prognostic value of serial lactate measurement in equine acute colitis warrants investigation.

HYPOTHESIS

Serial lactate concentrations are predictive of outcome in horses with colitis.

ANIMALS

A total of 101 horses with colitis.

METHODS

Retrospective study. Plasma L-lactate concentrations were measured at admission and at 4-8 and 24 hours after admission. Associations between admission, early (4-8 hours) and late (24 hours) lactate concentrations, and survival status were determined. The percent reduction in lactate concentration between admission and the early time point, and between admission and the late time point, was calculated. Using a cutoff value, associations between percent reduction in lactate and survival status and associations between percent reduction in lactate and clinical and clinicopathologic data were determined.

RESULTS

There was no association between admission plasma lactate concentration and survival status (P = .26). The 4-8 and 24 hour after admission lactate concentrations were associated with survival status (P = .023, .013, respectively). Lactate cutoffs of ≤2.3 and ≤1.5 mmol/L had the maximum sensitivity and specificity for predicting survival at the 4-8 and 24 hour time points, respectively. When lactate reduction ≥30% at 4-8 hours and ≥50% at 24 hours after admission were used as the cutoffs, the percent reduction of lactate concentration was significantly associated with survival (P = .012 and .019, respectively).

CONCLUSION AND CLINICAL IMPORTANCE

The prognostic ability of serial measurement of blood lactate concentration warrants prospective study as a measure of therapeutic response in horses with colitis.

Treatment of patients with ethylene glycol or methanol poisoning: focus on fomepizole

Ethylene glycol (EG) and methanol are responsible for life-threatening poisonings. Fomepizole, a potent alcohol dehydrogenase (ADH) inhibitor, is an efficient and safe antidote that prevents or reduces toxic EG and methanol metabolism. Although no study has compared its efficacy with ethanol, fomepizole is recommended as a first-line antidote. Treatment should be started as soon as possible, based on history and initial findings including anion gap metabolic acidosis, while awaiting measurement of alcohol concentration. Administration is easy (15 mg/kg-loading dose, either intravenously or orally, independent of alcohol concentration, followed by intermittent 10 mg/kg-doses every 12 hours until alcohol concentrations are <30 mg/dL). There is no need to monitor fomepizole concentrations. Administered early, fomepizole prevents EG-related renal failure and methanol-related visual and neurological injuries. When administered prior to the onset of significant acidosis or organ injury, fomepizole may obviate the need for hemodialysis. When dialysis is indicated, 1 mg/kg/h-continuous infusion should be provided to compensate for its elimination. Side-effects are rarely serious and with a lower occurrence than ethanol. Fomepizole is contraindicated in case of allergy to pyrazoles. It is both efficacious and safe in the pediatric population, but is not recommended during pregnancy. In conclusion, fomepizole is an effective and safe first-line antidote for EG and methanol intoxications.

Blood lactate monitoring in critically ill patients: a systematic health technology assessment

OBJECTIVE

To decide whether the use of blood lactate monitoring in critical care practice is appropriate. We performed a systematic health technology assessment as blood lactate monitoring has been implemented widely but its clinical value in critically ill patients has never been evaluated properly.

DATA SOURCE

PubMed, other databases, and citation review.

STUDY SELECTION

We searched for lactate combined with critically ill patients as the target patient population. Two reviewers independently selected studies based on relevance for the following questions: Does lactate measurement: 1) perform well in a laboratory setting? 2) provide information in a number of clinical situations? 3) relate to metabolic acidosis? 4) increase workers' confidence? 5) alter therapeutic decisions? 6) result in benefit to patients? 7) result in similar benefits in your own setting? 8) result in benefits which are worth the extra costs?

DATA EXTRACTION AND SYNTHESIS

We concluded that blood lactate measurement in critically ill patients: 1) is accurate in terms of measurement technique but adequate understanding of the (an)aerobic etiology is required for its correct interpretation; 2) provides not only diagnostic but also important prognostic information; 3) should be measured directly instead of estimated from other acid-base variables; 4) has an unknown effect on healthcare workers' confidence; 5) can alter therapeutic decisions; 6) could potentially improve patient outcome when combined with a treatment algorithm to optimize oxygen delivery, but this has only been shown indirectly; 7) is likely to have similar benefits in critical care settings worldwide; and 8) has an unknown cost-effectiveness.

CONCLUSIONS

The use of blood lactate monitoring has a place in risk-stratification in critically ill patients, but it is unknown whether the routine use of lactate as a resuscitation end point improves outcome. This warrants randomized controlled studies on the efficacy of lactate-directed therapy.

Ethylene glycol poisoning presenting with a falsely elevated lactate level

Early diagnosis of ethylene glycol poisoning is crucial in order to prevent morbidity and mortality. However, diagnosis can sometimes be delayed because of the false elevation of lactate in some chemistry analyzers as a result of the interference of glycolate, a metabolite of ethylene glycol. We present a case of ethylene glycol poisoning presenting with a falsely elevated lactate level on a blood gas analyzer in the emergency department. Given the fact that nowadays there is a marked increase in use of point-of-care analyzers, one should be aware of possible false readings since they use different methods of measuring compared with clinical chemistry analyzers. On the other hand, measuring a "lactate gap" using two different technologies, only one of which is sensitive to glycolate, could be a clinically efficient way to make the diagnosis of advanced ethylene glycol poisoning in the emergency department or other critical care setting.

Metabolic acidosis in the critically ill: part 2. Causes and treatment

The correct identification of the cause, and ideally the individual acid, responsible for metabolic acidosis in the critically ill ensures rational management. In Part 2 of this review, we examine the elevated (corrected) anion gap acidoses (lactic, ketones, uraemic and toxin ingestion) and contrast them with nonelevated conditions (bicarbonate wasting, renal tubular acidoses and iatrogenic hyperchloraemia) using readily available base excess and anion gap techniques. The potentially erroneous interpretation of elevated lactate signifying cell ischaemia is highlighted. We provide diagnostic and therapeutic guidance when faced with a high anion gap acidosis, for example pyroglutamate, in the common clinical scenario 'I can't identify the acid--but I know it's there'. The evidence that metabolic acidosis affects outcomes and thus warrants correction is considered and we provide management guidance including extracorporeal removal and fomepizole therapy.

Toxic alcohol ingestions: clinical features, diagnosis, and management

Alcohol-related intoxications, including methanol, ethylene glycol, diethylene glycol, and propylene glycol, and alcoholic ketoacidosis can present with a high anion gap metabolic acidosis and increased serum osmolal gap, whereas isopropanol intoxication presents with hyperosmolality alone. The effects of these substances, except for isopropanol and possibly alcoholic ketoacidosis, are due to their metabolites, which can cause metabolic acidosis and cellular dysfunction. Accumulation of the alcohols in the blood can cause an increment in the osmolality, and accumulation of their metabolites can cause an increase in the anion gap and a decrease in serum bicarbonate concentration. The presence of both laboratory abnormalities concurrently is an important diagnostic clue, although either can be absent, depending on the time after exposure when blood is sampled. In addition to metabolic acidosis, acute renal failure and neurologic disease can occur in some of the intoxications. Dialysis to remove the unmetabolized alcohol and possibly the organic acid anion can be helpful in treatment of several of the alcohol-related intoxications. Administration of fomepizole or ethanol to inhibit alcohol dehydrogenase, a critical enzyme in metabolism of the alcohols, is beneficial in treatment of ethylene glycol and methanol intoxication and possibly diethylene glycol and propylene glycol intoxication. Given the potentially high morbidity and mortality of these intoxications, it is important for the clinician to have a high degree of suspicion for these disorders in cases of high anion gap metabolic acidosis, acute renal failure, or unexplained neurologic disease so that treatment can be initiated early.

Falsely elevated point-of-care lactate measurement after ingestion of ethylene glycol

BACKGROUND

A patient presented with severe acidosis and a point-of-care lactate measurement of 42 mmol/L. Mesenteric ischemia was suspected, with a potential need for laparotomy; however, plasma lactate measurements were below 4 mmol/L. Ethylene glycol ingestion was subsequently diagnosed. We therefore wished to determine why discrepancies in lactate measurements occur and whether this "lactate gap" could be clinically useful.

METHODS

We phlebotomized blood, added various concentrations of metabolites of ethylene glycol, and tested the resulting samples with the 5 most common lactate analyzers.

RESULTS

With the Radiometer 700 point-of-care analyzer, glycolate addition resulted in an artifactual, massive lactate elevation, even at low glycolate concentrations. Another major ethylene glycol metabolite, glyoxylate (but not oxalate or formate), caused similar elevations. The i-STAT and Bayer point-of-care analyzers and the Beckman and Vitros laboratory analyzers reported minimal lactate elevations. Lactate gap was determined by comparing the Radiometer result with the corresponding result from any of the other analyzers.

INTERPRETATION

We demonstrated how inappropriate laparotomy or delayed therapy might occur if clinicians are unaware of this phenomenon or have access to only a single analyzer. We also showed that lactate gap can be exploited to expedite treatment, diagnose late ethylene-glycol ingestion and terminate dialysis. By comparing lactate results from the iSTAT or Bayer devices with that from the Radiometer, ethylene-glycol ingestion can be diagnosed at the point of care. This can expedite diagnosis and treatment by hours, compared with waiting for laboratory results for plasma ethylene glycol.

Primer on clinical acid-base problem solving

Acid-base problem solving has been an integral part of medical practice in recent generations. Diseases discovered in the last 30-plus years, for example, Bartter syndrome and Gitelman syndrome, D-lactic acidosis, and bulimia nervosa, can be diagnosed according to characteristic acid-base findings. Accuracy in acid-base problem solving is a direct result of a reproducible, systematic approach to arterial pH, partial pressure of carbon dioxide, bicarbonate concentration, and electrolytes. The 'Rules of Five' is one tool that enables clinicians to determine the cause of simple and complex disorders, even triple acid-base disturbances, with consistency. In addition, other electrolyte abnormalities that accompany acid-base disorders, such as hypokalemia, can be incorporated into algorithms that complement the Rules and contribute to efficient problem solving in a wide variety of diseases. Recently urine electrolytes have also assisted clinicians in further characterizing select disturbances. Acid-base patterns, in many ways, can serve as a 'common diagnostic pathway' shared by all subspecialties in medicine. From infectious disease (eg, lactic acidemia with highly active antiviral therapy therapy) through endocrinology (eg, Conn's syndrome, high urine chloride alkalemia) to the interface between primary care and psychiatry (eg, bulimia nervosa with multiple potential acid-base disturbances), acid-base problem solving is the key to unlocking otherwise unrelated diagnoses. Inasmuch as the Rules are clinical tools, they are applied throughout this monograph to diverse pathologic conditions typical in contemporary practice.

Artifactual elevation of lactate in ethylene glycol poisoning

The diagnosis of ethylene glycol poisoning is based on nonspecific clinical symptoms and signs and indirect and direct laboratory measurement. Few institutions have timely access to direct measurement of ethylene glycol. As a result, diagnosis sometimes can be delayed and therapy initiated late. We present two cases of ethylene glycol poisoning. These cases demonstrate the need to recognize the false elevation of lactate in some chemistry analyzers due to the interference of glycolic acid, a metabolite of ethylene glycol. Using the "lactate gap" in comparing the measurement of lactate with two commonly used chemical analyzers aids in differentiating ethylene glycol poisoning from lactic acidosis.