Purpose of each in investigations each enzyme purpose and why see them in psychiatry medication

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Investigation Panel - Purpose of Each Test & Psychiatric Relevance

Based on the investigation form from Bharati Vidyapeeth Medical College, here is a complete breakdown of every enzyme and test - what it measures, its clinical purpose, and specifically why it appears in psychiatric monitoring.

HAEMATOLOGY

Test	Normal	Purpose	Psychiatric Relevance
Hb%	M: 13-18 g/dL, F: 12-15 g/dL	Measures haemoglobin - oxygen-carrying capacity	Anaemia causes fatigue, cognitive slowing, depression-like symptoms. Clozapine and carbamazepine can cause aplastic anaemia
WBCs	5000-10000 Cu/mm	Total white cell count - immune function	Clozapine causes agranulocytosis (WBC <3000, ANC <1500) - mandatory weekly/fortnightly monitoring. Carbamazepine also causes leucopenia
Platelets	1.5-4.5 lakh/cu mm	Clotting, haemostasis	Valproate causes dose-related thrombocytopenia and platelet dysfunction. Must check before surgery or if bruising occurs
ESR	F: 0-15, M: 0-20 mm/hr	Non-specific inflammatory marker	Elevated in infection, autoimmune disease, malignancy - all of which can mimic psychiatric illness

RENAL FUNCTION TESTS (RFT)

Test	Normal	Purpose
BSL (Blood Sugar Level)	70-120 mg/dL	Plasma glucose
BUL (Blood Urea Level)	12-45 mg/dL	Urea - end product of protein catabolism
Sr. Creatinine	0.7-1.4 mmol/L	Glomerular filtration marker
Sr. Na+	135-145 mmol/L	Sodium - fluid balance
Sr. K+	3.8-5.0 mmol/L	Potassium - cardiac & nerve conduction
Sr. Cl-	95-105 mmol/L	Chloride - acid-base balance

Why these matter in psychiatry:

BSL: Second-generation antipsychotics (SGAs) - especially clozapine, olanzapine, quetiapine - cause weight gain, insulin resistance, and type 2 diabetes mellitus. Baseline and monitoring BSL is mandatory with these drugs.

BUL & Creatinine: Lithium is almost entirely excreted by the kidney - any reduction in GFR causes lithium to accumulate to toxic levels. According to Kaplan & Sadock's, "elevations in BUN often are associated with impaired clearance of lithium... Cr clearance is often assessed in patients taking lithium." Toxicity causes tremor, ataxia, confusion, and can be fatal.

Na+ (Sodium): Carbamazepine and oxcarbazepine cause SIADH - hyponatremia which can present as delirium, seizures, or mimic worsening psychiatric illness. The Comprehensive Textbook notes: "Hyponatremia is seen in psychogenic polydipsia and SIADH and in response to certain medications, such as oxcarbazepine and carbamazepine."

K+ (Potassium): Eating disorders (common in psychiatric patients) with purging cause hypokalaemia. Hypokalemia also prolongs the QTc interval, which is already lengthened by many antipsychotics (haloperidol, ziprasidone, quetiapine) - a potentially fatal combination leading to Torsades de Pointes.

LIVER FUNCTION TESTS (LFT) - THE ENZYMES

These are the most important section for psychiatric drug monitoring.

S.G.O.T. (SGOT) = AST (Aspartate Aminotransferase)

Normal: 10-40 units
Where found: Liver, heart, skeletal muscle, kidneys, lungs
What elevation means: Hepatocellular damage; in alcoholic liver disease, AST is typically more elevated than ALT (AST:ALT ratio >2:1 strongly suggests alcohol)
Psychiatric relevance: Valproate causes transient transaminitis (rise in both AST and ALT). All mood stabilisers, antipsychotics, and TCAs are hepatically metabolised - liver damage reduces their clearance and increases toxicity risk

S.G.P.T. (SGPT) = ALT (Alanine Aminotransferase)

Normal: 5-35 units
Where found: Most specific to the liver (more specific than AST)
What elevation means: Hepatocellular injury - drug-induced or viral hepatitis causes ALT > AST
Psychiatric relevance: In drug-induced liver disease (e.g., from valproate, carbamazepine, antipsychotics), ALT is often more elevated than AST. Kaplan & Sadock states: "Various psychotropic medications, including valproate, may induce transient transaminitis. Dosage of second-generation antipsychotics and some antidepressants must be reduced in patients with impaired hepatic function."

Key clinical rule: AST:ALT >2:1 = suspect alcohol. ALT > AST = suspect drug/viral hepatitis.

Alkaline Phosphatase (ALP)

Normal: 70-251 U/L
Where found: Liver (biliary canaliculi), bone, kidney, thyroid, placenta
What elevation means: Cholestasis/biliary obstruction, bone disease, infiltrative liver disease
Psychiatric relevance: Kaplan & Sadock's Comprehensive Textbook explicitly states: "Levels of alkaline phosphatase may be elevated in response to some psychiatric medications, most notably the phenothiazines" (e.g., chlorpromazine, thioridazine). Phenothiazines can cause cholestatic jaundice - a form of drug-induced liver injury where bile flow is obstructed.

Total Bilirubin / Direct Bilirubin / Indirect Bilirubin

Normal: Total 0.1-1.2 mg/dL, Direct 0.1-0.4 mg/dL, Indirect 0.1-0.6 mg/dL
What it measures: Breakdown product of haem; tests hepatic conjugation and biliary excretion
Psychiatric relevance: Elevated bilirubin occurs with phenothiazine-induced cholestatic jaundice. Valproate can cause severe hepatotoxicity (especially in children under 2 on polypharmacy) causing elevated bilirubin. Protein binding of drugs is altered in jaundice - raising free drug levels and toxicity risk.

Sr. Proteins / Sr. Albumin / Globulin

Normal: Proteins 5.5-8.0 g/dL; Albumin 3.5-5.0 g/dL; Globulin 1.5-3.0 g/dL
Why critical in psychiatry: "Many psychiatric medications are protein bound. Low levels of serum total protein result in a high fraction of an ingested drug remaining in the unbound (active) state. High levels of unbound drug increase the active effects and side effects." (Kaplan & Sadock's Comprehensive Textbook, 2021). For example: valproate is ~90% protein bound - in hypoalbuminaemia, much more free valproate circulates, causing toxicity at "normal" total drug levels.

Protime (PT) - Factors II, VII, X (PROTIME II VII X)

Normal: 10-14 seconds
Why it matters in psychiatry: The liver synthesises clotting factors. A prolonged PT indicates impaired synthetic liver function - a red flag for serious hepatic damage from medications (valproate, carbamazepine). Also relevant before ECT procedures and when adding anticoagulants.

COAGULATION

Test	Normal	Purpose
BT (Bleeding Time)	2-7 sec	Primary haemostasis, platelet plug formation
CT (Clotting Time)	5-10 sec	Overall coagulation cascade

Psychiatric relevance: Valproate inhibits platelet aggregation and can reduce platelet count. SSRIs also impair platelet function (by depleting platelet serotonin). Both become important before any invasive procedure.

LIPID PROFILE

Test	Normal	Purpose
Cholesterol	150-250 mg/dL	Total cholesterol - cardiovascular risk
Triglycerides	65-165 mg/dL	TG - another cardiovascular risk marker
Lipids	400-1000 mg/dL	Total lipids
HDL	>60 mg/dL	"Good" cholesterol - cardioprotective
LDL	<130 mg/dL	"Bad" cholesterol - atherogenic

Psychiatric relevance: SGAs (especially clozapine, olanzapine, quetiapine) cause metabolic syndrome - a triad of weight gain, dyslipidaemia (high TG, low HDL), and glucose intolerance. This dramatically increases cardiovascular risk. Monitoring this lipid panel at baseline and every 3-6 months on SGAs is recommended by all major guidelines. This is now a well-recognised side effect that has prompted the use of metformin co-prescription with some antipsychotics.

CARDIAC & MUSCLE ENZYMES

LDH (Lactate Dehydrogenase)

Normal: 240-480 U/L
Where found: RBCs, heart, liver, skeletal muscle, kidneys
What elevation means: Tissue destruction - MI, haemolysis, lymphoma, PE
Psychiatric relevance: Elevated in Neuroleptic Malignant Syndrome (NMS) - a life-threatening reaction to antipsychotics. Also elevated with rhabdomyolysis from restraint or agitated patients.

CPK (Creatine Phosphokinase / CK)

Normal: Listed here as 37°C (reference temperature) - standard normal is up to ~200 U/L in men
Where found: Skeletal muscle (CK-MM), heart (CK-MB), brain (CK-BB)
Psychiatric relevance - CRITICAL: CPK is a cardinal marker of NMS. In NMS caused by antipsychotics (haloperidol, fluphenazine, any dopamine-blocker), severe muscle rigidity leads to rhabdomyolysis with CPK values often exceeding 1000-100,000 U/L. Rosen's Emergency Medicine confirms that creatine kinase level is the first test to check when NMS is suspected. Very high CPK also causes renal tubular damage - hence the BUL/creatinine are checked together.

CKMB (CK-MB Isoenzyme)

Where found: Predominantly cardiac muscle (normally <5% of total CK)
What elevation means: Myocardial injury/MI
Psychiatric relevance: Clozapine causes myocarditis and cardiomyopathy (especially in first 2 months of treatment). CKMB elevation, along with troponin and ECG changes, indicates clozapine-induced myocarditis - a medical emergency requiring immediate drug cessation. Patients on clozapine who develop unexplained tachycardia, fever, or chest pain must have CKMB checked.

PANCREATIC ENZYMES

Alkaline Phosphatase (covered above - also rises in pancreatic disease)

Sr. Amylase

Normal: 25-125 U/L
Where found: Pancreas (P-type), salivary glands (S-type)
What elevation means: Acute pancreatitis, salivary gland disease, ectopic pregnancy
Psychiatric relevance:
1. Valproate is associated with acute pancreatitis - amylase monitoring is indicated if a patient on valproate develops abdominal pain
2. Eating disorders (bulimia nervosa) cause parotid hypertrophy and elevated salivary amylase - Kaplan & Sadock's notes "serum amylase is often assessed in bulimic patients"
3. Clozapine-induced hypersalivation can occasionally be associated with parotitis

Sr. Lipase

Normal: 0-60 U/L
Where found: Pancreatic acinar cells (more specific than amylase for pancreatitis)
What elevation means: Acute pancreatitis - more specific and longer lasting than amylase
Psychiatric relevance: Valproate-induced pancreatitis is a rare but serious side effect. Lipase is the confirmatory test when amylase is ambiguous. Also elevated in patients with alcohol use disorder with pancreatic involvement.

HIV & WIDAL

Test	Purpose	Psychiatric Relevance
HIV	Screens for HIV infection	HIV directly causes neuropsychiatric syndromes (HIV encephalopathy, neurocognitive disorder). Also, HIV-positive patients on antiretrovirals have major drug-drug interactions with psychotropics (especially through CYP450 enzymes)
WIDAL	Agglutination test for typhoid fever (Salmonella typhi)	Typhoid encephalopathy presents with delirium, psychosis, and personality change - must be excluded in fever + psychiatric presentation

Summary: Why Psychiatry Needs All These Investigations

The core reasons can be grouped into 4 categories:

Baseline before starting medications - LFTs (for hepatically-metabolised drugs), RFTs (for lithium), CBC (for clozapine), lipids & BSL (for SGAs), CPK (for antipsychotics)
Monitoring for drug toxicity - Valproate: LFTs, amylase, lipase, platelets; Lithium: renal function; Clozapine: WBC (agranulocytosis), CKMB (myocarditis), CPK (NMS); Antipsychotics: CPK (NMS), metabolic panel
Excluding organic causes of psychiatric symptoms - Thyroid disease, hepatic encephalopathy, electrolyte disturbances, infections (HIV, typhoid, syphilis) all mimic psychiatric illness
Special populations - Eating disorders: amylase, albumin, K+, phosphorus; Alcohol use disorder: LFTs, GGT, MCV; Substance use: LFTs, RFTs

Sources: Kaplan & Sadock's Comprehensive Textbook of Psychiatry, 11th Ed (9781975175733); Kaplan & Sadock's Synopsis of Psychiatry (9781975145569); Rosen's Emergency Medicine, 9th Ed (9780323757898)

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